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  • 251.
    Hendrickx, Koen
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Solar Forcing of Nitric Oxide in the Upper Atmosphere2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The forcing of the Sun on Earth's atmosphere manifests itself via solar radiation and energetic particle precipitation (EPP), which variations are most noticeable in the upper regions of the atmosphere. A key species in the lower thermosphere, which is influenced by solar forcing, is nitric oxide (NO). An NO reservoir is present in the lower thermosphere, from which NO-rich air can be transported downward into the mesosphere and stratosphere, where it takes part in catalytic ozone destruction cycles. For climate models to correctly simulate the solar forcing on our climate, the processes of NO production and destruction, as well as the descent into the lower atmosphere, must be understood and accurately represented.

    In this thesis, observations from the Solar Occultation For Ice Experiment (SOFIE) instrument onboard the Aeronomy of Ice in the Mesosphere (AIM) satellite are used to investigate temporal characteristics of NO in the mesosphere and lower thermosphere. We have developed a diagnostic method to determine the relative importance of the NO physical drivers throughout the lower thermosphere. The method shows that, at high latitudes, precipitating auroral electrons dominantly drive NO variations. Comparisons with NO measurements by the Student Nitric Oxide Experiment (SNOE), made almost a decade earlier, reveal that the impact of this forcing on NO appears to be invariant throughout the 11 year solar cycle.

    On shorter timescales, we have shown a clear signature of the reoccurring 27 day geomagnetic impact on NO concentrations during summer and winter, with subsequent descent into the lower mesosphere during winter. The occurrence of medium energy electrons, which precipitate to mesospheric altitudes, results in a further increase of the descending NO flux. This complicates the determination of the relative contribution of the EPP direct and indirect effect on NO, i.e. separating direct NO production from downwards transported NO, respectively, in NO enhancements at a certain altitude. Using a full-range energy spectrum from the Polar-orbiting Operational Environmental Satellites (POES), we have been able to disentangle the direct and indirect EPP effect on Southern hemispheric NO during a geomagnetic storm in 2010.

    Simulations of NO by the Whole Atmosphere Community Climate Model with Specified Dynamics (SD-WACCM) model reveal that the model predicts a too high climatological mean, while the short term variability is too low, as compared to SOFIE. However, even though the dynamical transport in both model and observations agrees very well, the descending NO fluxes are too low in the model.

    In conclusion, the results of this thesis provide a better understanding of NO variability from an observational standpoint and will enable better model representations in the future.

  • 252.
    Hendrickx, Koen
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Megner, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Gumbel, Jörg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Siskind, D. E.
    Orsolini, Y. J.
    Nesse Tyssøy, H.
    Hervig, M.
    Observation of 27-day solar cycles in mesospheric production and descent of EPP-produced NO2015Inngår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 120, nr 10, s. 8978-8988Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nitric oxide (NO) is produced by energetic particle precipitation (EPP) in the mesosphere-lower thermosphere (MLT) region, and during the polar winter, NO can descend to stratospheric altitudes where it destroys ozone. In this paper, we study the general scenario, as opposed to a case study, of NO production in the thermosphere due to energetic particles in the auroral region. We first investigate the relationship between NO production and two geomagnetic indices. The analysis indicates that the auroral electrojet index is a more suitable proxy for EPP-produced NO than the typically used midlatitude Ap index. In order to study the production and downward transport of NO from the lower thermosphere to the mesosphere, we perform superposed epoch analyses on NO observations made by the Solar Occultation For Ice Experiment instrument on board the Aeronomy of Ice in the Mesosphere satellite. The epoch analysis clearly shows the impact of the 27 day solar cycle on NO production. The effect is observed down to an altitude range of about 50 km to 65 km, depending on the hemisphere and the occurrence of stratospheric warmings. Initially, a rapid downward transport is noted during the first 10 days after EPP onset to an altitude of about 80–85 km, which is then followed by a slower downward transport of approximately 1–1.2 km/d to lower mesospheric altitudes in the order of 30 days.

  • 253.
    Hendrickx, Koen
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Megner, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Marsh, Daniel R.
    Gumbel, Jörg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Strandberg, Rickard
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Martinsson, Felix
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Relative Importance of Nitric Oxide Physical Drivers in the Lower Thermosphere2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 19, s. 10081-10087Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nitric oxide (NO) observations from the Solar Occultation for Ice Experiment and Student Nitric Oxide Explorer satellite instruments are investigated to determine the relative importance of drivers of short-term NO variability. We study the variations of deseasonalized NO anomalies by removing a climatology, which explains between approximately 70% and 90% of the total NO budget, and relate them to variability in geomagnetic activity and solar radiation. Throughout the lower thermosphere geomagnetic activity is the dominant process at high latitudes, while in the equatorial region solar radiation is the primary source of short-term NO changes. Consistent results are obtained on estimated geomagnetic and radiation contributions of NO variations in the two data sets, which are nearly a decade apart in time. The analysis presented here can be applied to model simulations of NO to investigate the accuracy of the parametrized physical drivers.

  • 254. Henschel, Henning
    et al.
    Acosta Navarro, Juan Camilo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Yli-Juuti, Taina
    Kupiainen-Määttä, Oona
    Olenius, Tinja
    Ortega, Ismael K.
    Clegg, Simon L.
    Kurtén, Theo
    Riipinen, Ilona
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Vehkamäki, Hanna
    Hydration of Atmospherically Relevant Molecular Clusters: Computational Chemistry and Classical Thermodynamics2014Inngår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, nr 14, s. 2599-2611Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Formation of new particles through clustering of molecules from condensable vapors is a significant source for atmospheric aerosols. The smallest clusters formed in the very first steps of the condensation process are, however, not directly observable by experimental means. We present here a comprehensive series of electronic structure calculations on the hydrates of clusters formed by up to four molecules of sulfuric acid, and up to two molecules of ammonia or dimethylamine. Though clusters containing ammonia, and certainly dimethylamine, generally exhibit lower average hydration than the pure acid clusters, populations of individual hydrates vary widely. Furthermore, we explore the predictions obtained using a thermodynamic model for the description of these hydrates. The similar magnitude and trends of hydrate formation predicted by both methods illustrate the potential of combining them to obtain more comprehensive models. The stabilization of some clusters relative to others due to their hydration is highly likely to have significant effects on the overall processes that lead to formation of new particles in the atmosphere.

  • 255. Herbert, Corentin
    et al.
    Caballero, Rodrigo
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Bouchet, Freddy
    Atmospheric Bistability and Abrupt Transitions to Superrotation: Wave-Jet Resonance and Hadley Cell Feedbacks2020Inngår i: Journal of the Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 77, nr 1, s. 31-49Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strong eastward jets at the equator have been observed in many planetary atmospheres and simulated in numerical models of varying complexity. However, the nature of the transition from a conventional state of the general circulation, with easterlies or weak westerlies in the tropics, to such a superrotating state remains unclear. Is it abrupt or continuous? This question may have far-reaching consequences, as it may provide a mechanism for abrupt climate change in a planetary atmosphere, both through the loss of stability of the conventional circulation and through potential noise-induced transitions in the bistability range. We study two previously suggested feedbacks that may lead to bistability between a conventional and a superrotating state: the Hadley cell feedback and a wave-jet resonance feedback. We delineate the regime of applicability of these two mechanisms in a simple model of zonal acceleration budget at the equator. Then we show using numerical simulations of the axisymmetric primitive equations that the wave-jet resonance feedback indeed leads to robust bistability, while the bistability governed by the Hadley cell feedback, although observed in our numerical simulations, is much more fragile in a multilevel model.

  • 256. Hicks, Kevin
    et al.
    Kuylenstierna, Johan
    Owen, Anne
    Dentener, Frank
    Seip, Hans-Martin
    Rodhe, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Soil sensitivity to acidification in Asia: Status and prospects2008Inngår i: Ambio, Vol. 37, nr 4, s. 295-303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Exceedance of steady-state critical loads for soil acidification is consistently found in southern China and parts of SE Asia, but there is no evidence of impacts outside of China. This study describes a methodology for calculating the time to effects for soils sensitive to acidic deposition in Asia under potential future sulfur (S), nitrogen (N), and calcium (Ca) emission scenarios. The calculations are matched to data availability in Asia to produce regional-scale maps that provide estimates of the time (y) it will take for soil base saturation to reach a critical limit of 20% in response to acidic inputs. The results show that sensitive soil types in areas of South, Southeast, and East Asia, including parts of southern China, Burma, Hainan, Laos, Thailand, Vietnam, and the Western Ghats of India, may acidify to a significant degree on a 0–50 y timescale, depending on individual site management and abiotic and biotic characteristics. To make a clearer assessment of risk, site-specific data are required for soil chemistry and deposition (especially base cation deposition); S and N retention in soils and ecosystems; and biomass harvesting and weathering rates from sites across Asia representative of different soil and vegetation types and management regimes. National and regional assessments of soils using the simple methods described in this paper can provide an appreciation of the time dimension of soil acidification–related impacts and should be useful in planning further studies and, possibly, implementing measures to reduce risks of acidification

  • 257.
    Hieronymus, Jenny
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Walin, Gösta
    Unravelling the land source: an investigation of the processes contributing to the oceanic input of DIC and alkalinity2013Inngår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, s. 19683-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In models of the marine carbon system, it is important to correctly represent riverine and aerial inputs of dissolved inorganic carbon (DIC) and alkalinity. We have examined the different processes contributing to this exchange. In terms of DIC, we have divided the fluxes into their internal component, constituting the carbon ultimately derived from the atmosphere, and their external component originating from rocks. We find that the only process contributing to external DIC input is carbonate and fossil carbon weathering and that erosion of organic matter ultimately constitutes a DIC sink. A number of both riverine and aerial inputs affect the alkalinity. Beside carbonate and silicate weathering, we examine processes of pyrite weathering, aerial input of sulphuric acid, and riverine and aerial inputs of various nitrogen species. Using the observation that, in the ocean, the nitrate concentration follows that of phosphate, we assume a steady state in nitrate. This leads to the surprising result that the only processes affecting the alkalinity is riverine input of nitrate, constituting an alkalinity source and input of ammonia, constituting an alkalinity sink. Furthermore, we compare the flux sizes. As expected, carbonate and silicate weathering has the largest effect on alkalinity, though we note that burial of pyrite might be of importance during periods of large-scale anoxia.

  • 258.
    Hieronymus, Magnus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Nycander, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Interannual Variability of the Overturning and Energy Transport in the Atmosphere and Ocean During the Late Twentieth Century with Implications for Precipitation and Sea Level2020Inngår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 33, nr 1, s. 317-338Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The overturning circulations in the atmosphere and ocean transport energy from the tropics to higher latitudes and thereby modulate Earth's climate. The interannual variability in the overturning over the last 40 years is found to be dominated by two coupled atmosphere-ocean modes. The first is related to the meridional motion of the intertropical convergence zone and the second to El Nino. Both modes have a strong influence on the sea level variability in the tropical Indo-Pacific Ocean. The interannual variability of the cross-equatorial energy transport is dominated by the first mode, and the variability is larger in the Indo-Pacific Ocean than in the Atlantic Ocean or the atmosphere. Our results suggest an important role of oceanic energy transport in setting precipitation patterns in the tropics and a key role of the Indo-Pacific Ocean as a climate modulator.

  • 259.
    Hieronymus, Magnus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Nycander, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    The budgets of heat and salinity in NEMO2013Inngår i: Ocean Modelling, ISSN 1463-5003, E-ISSN 1463-5011, Vol. 67, s. 28-38Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The near steady state heat and salinity budgets under surfaces of constant depth are examined in the Nucleus for European Modelling of the Ocean (NEMO) model. It is seen that the heat fluxes in NEMO are difficult to reconcile with the idea of a deep ocean in advection-diffusion balance. Some reasons for this are that the resolved heat advection is downward above 2000 m, and that geothermal heating is, in fact, a major heat source in the deeper parts of the domain. It is also seen that isoneutral diffusion gives a very large contribution to the budgets and that the fluxes from isoneutral diffusion is in general upward. It is explained how the sign of these fluxes depends on the stratification. The heat budget for the upper 100 m of the ocean is seen to be dominated by penetrative shortwave radiation, which is so influential that we would have a mixed layer of considerable thickness even in the absence of other sources of turbulent mixing. Penetrative shortwave radiation is therefore a considerable source of potential energy.

  • 260.
    Hind, Alistair
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Moberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Past millennial solar forcing magnitude: A statistical hemispheric-scale climate model versus proxy data comparison2013Inngår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 41, nr 9-10, s. 2527-2537Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A set of global climatemodel simulations for the lastthousand years developed by the Max Planck Institute is comparedwith paleoclimate proxy data and instrumental data,focusing on surface temperatures for land areas between 30 and75N. The proxy data are obtained from six previously publishedNorthern Hemispheric-scale temperature reconstructions, here recalibratedfor consistency, which are compared with the simulationsutilizing a newly developed statistical framework forranking several competing simulations by means of their statisticaldistance against past climate variations. The climate modelsimulations are driven by either ‘‘low’’ or ‘‘high’’ solar forcingamplitudes (0.1 and 0.25 % smaller total solar irradiance in the Maunder Minimum period compared to the present) in addition toseveral other known climate forcings of importance. Our resultsindicate that the high solar forcing amplitude results in a poorermatch with the hemispheric-scale temperature reconstructionsand lends stronger statistical support for the low-amplitude solarforcing. However, results are likely conditional upon the sensitivityof the climate model used and strongly dependent on thechoice of temperature reconstruction, hence a greater consensus isneeded regarding the reconstruction of past temperatures as thiscurrently provides a great source of uncertainty.

  • 261. Hodson, Andy
    et al.
    Roberts, Tjarda Jane
    Engvall, Anne-Christin
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Holmen, Kim
    Mumford, Paul
    Glacier ecosystem response to episodic nitrogen enrichment in Svalbard, European High Arctic2010Inngår i: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 98, nr 03-jan, s. 171-184Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We describe the climatology, hydrology and biogeochemistry of an extreme nitrogen deposition event that occurred in the highly glacierised environment of the European High Arctic during June 1999. Meteorological analysis, three-dimensional air mass trajectories and a 3D transport model show that blocking high pressures over Scandinavia and the rapid advection of western European pollution toward Svalbard were sufficient to cause the most concentrated (1.15 ppm NO3-N and 1.20 ppm NH4-N), high magnitude (total 26 mm and up to 2.4 mm h(-1) at 30 m above sea level) nitrogen deposition event on record in this sensitive, high Arctic environment (78.91A degrees A N, 11.93A degrees A E). Since the event occurred when much of the catchment remained frozen or under snow cover, microbial utilisation of nitrogen within snowpacks and perennially unfrozen subglacial sediments, rather than soils, were mostly responsible for reducing N export. The rainfall event occurred long before the annual subglacial outburst flood and so prolonged (ca. 10 day) water storage at the glacier bed further enhanced the microbial assimilation. When the subglacial outburst eventually occurred, high runoff and concentrations of NO3 (-) (but not NH4 (+)) returned in the downstream rivers. Assimilation accounted for between 53 and 72% of the total inorganic nitrogen deposited during the event, but the annual NO3 (-) and NH4 (+) runoff yields were still enhanced by up to 5 and 40 times respectively. Episodic atmospheric inputs of reactive nitrogen can therefore directly influence the biogeochemical functioning of High Arctic catchments, even when microbial activity takes place beneath a glacier at a time when terrestrial soil ecosystems remain frozen and unresponsive.

  • 262. Hoffmann, Anne
    et al.
    Osterloh, Lukas
    Stone, Robert
    Lampert, Astrid
    Ritter, Christoph
    Stock, Maria
    Tunved, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Hennig, Tabea
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Boeckmann, Christine
    Li, Shao-Meng
    Eleftheriadis, Kostas
    Maturilli, Marion
    Orgis, Thomas
    Herber, Andreas
    Neuber, Roland
    Dethloff, Klaus
    Remote sensing and in situ measurements of tropospheric aerosol, a pamarcmip case study2012Inngår i: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 52, s. 56-66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, a closure experiment for tropospheric aerosol is presented. Aerosol size distributions and single scattering albedo from remote sensing data are compared to those measured in-situ. An aerosol pollution event on 4 April 2009 was observed by ground based and airborne lidar and photometer in and around Ny-Alesund, Spitsbergen, as well as by DMPS, nephelometer and particle soot absorption photometer at the nearby Zeppelin Mountain Research Station. The presented measurements were conducted in an area of 40 x 20 km around Ny-Alesund as part of the 2009 Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project (PAMARCMiP). Aerosol mainly in the accumulation mode was found in the lower troposphere, however, enhanced backscattering was observed up to the tropopause altitude. A comparison of meteorological data available at different locations reveals a stable multi-layer-structure of the lower troposphere. It is followed by the retrieval of optical and microphysical aerosol parameters. Extinction values have been derived using two different methods, and it was found that extinction (especially in the UV) derived from Raman lidar data significantly surpasses the extinction derived from photometer AOD profiles. Airborne lidar data shows volume depolarization values to be less than 2.5% between 500 m and 2.5 km altitude, hence, particles in this range can be assumed to be of spherical shape. In-situ particle number concentrations measured at the Zeppelin Mountain Research Station at 474 m altitude peak at about 0.18 mu m diameter, which was also found for the microphysical inversion calculations performed at 850 m and 1500 m altitude. Number concentrations depend on the assumed extinction values, and slightly decrease with altitude as well as the effective particle diameter. A low imaginary part in the derived refractive index suggests weakly absorbing aerosols, which is confirmed by low black carbon concentrations, measured at the Zeppelin Mountain as well as on board the Polar 5 aircraft.

  • 263.
    Holmström, Ingemar
    Stockholms universitet.
    An empirical and theoretical investigation of the vertical structure of large scale atmospheric flow.1964Doktoravhandling, med artikler (Annet vitenskapelig)
  • 264. Holtslag, A. A. M.
    et al.
    Svensson, Gunilla
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Baas, P.
    Basu, S.
    Beare, B.
    Beljaars, A. C. M.
    Bosveld, F. C.
    Cuxart, J.
    Lindvall, Jenny
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Steeneveld, G. J.
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Van de Wiel, B. J. H.
    STABLE ATMOSPHERIC BOUNDARY LAYERS AND DIURNAL CYCLES: Challenges for Weather and Climate Models2013Inngår i: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 94, nr 11, s. 1691-1706Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear-sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models, and large-eddy simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas, and Cabauw in the Netherlands. From these studies, we find that even for the noncloudy boundary layer important parameterization challenges remain.

  • 265. Hommel, R.
    et al.
    Eichmann, K. -U
    Aschmann, J.
    Bramstedt, K.
    Weber, M.
    von Savigny, C.
    Richter, A.
    Rozanov, A.
    Wittrock, F.
    Khosrawi, F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Bauer, R.
    Burrows, J. P.
    Chemical ozone loss and ozone mini-hole event during the Arctic winter 2010/2011 as observed by SCIAMACHY and GOME-22014Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, nr 7, s. 3247-3276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Record breaking loss of ozone (O-3) in the Arctic stratosphere has been reported in winter-spring 2010/2011. We examine in detail the composition and transformations occurring in the Arctic polar vortex using total column and vertical profile data products for O-3, bromine oxide (BrO), nitrogen dioxide (NO2), chlorine dioxide (OClO), and polar stratospheric clouds (PSC) retrieved from measurements made by SCIAMACHY (Scanning Imaging Absorption SpectroMeter for Atmospheric CHartography) onboard Envisat (Environmental Satellite), as well as total column ozone amount, retrieved from the measurements of GOME-2 (Global Ozone Monitoring Experiment) on MetOp-A (Meteorological Experimental Satellite). Similarly we use the retrieved data from DOAS (Differential Optical Absorption Spectroscopy) measurements made in Ny-Alesund (78.55 degrees N, 11.55 degrees E). A chemical transport model (CTM) has been used to relate and compare Arctic winter-spring conditions in 2011 with those in the previous year. In late winter-spring 2010/2011 the chemical ozone loss in the polar vortex derived from SCIAMACHY observations confirms findings reported elsewhere. More than 70% of O-3 was depleted by halogen catalytic cycles between the 425 and 525K isentropic surfaces, i.e. in the altitude range similar to 16-20 km. In contrast, during the same period in the previous winter 2009/2010, a typical warm Arctic winter, only slightly more than 20% depletion occurred below 20 km, while 40% of O-3 was removed above the 575K isentrope (similar to 23 km). This loss above 575K is explained by the catalytic destruction by NOx descending from the mesosphere. In both Arctic winters 2009/2010 and 2010/2011, calculated O-3 losses from the CTM are in good agreement to our observations and other model studies. The mid-winter 2011 conditions, prior to the catalytic cycles being fully effective, are also investigated. Surprisingly, a significant loss of O-3 around 60 %, previously not discussed in detail, is observed in mid-January 2011 below 500K (similar to 19 km) and sustained for approximately 1 week. The low O-3 region had an exceptionally large spatial extent. The situation was caused by two independently evolving tropopause elevations over the Asian continent. Induced adiabatic cooling of the stratosphere favoured the formation of PSC, increased the amount of active chlorine for a short time, and potentially contributed to higher polar ozone loss later in spring.

  • 266. Hong, J.
    et al.
    Hakkinen, S. A. K.
    Paramonov, M.
    Aijala, M.
    Hakala, J.
    Nieminen, T.
    Mikkila, J.
    Prisle, N. L.
    Kulmala, M.
    Riipinen, Ilona
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Bilde, M.
    Kerminen, V. -M
    Petaja, T.
    Hygroscopicity, CCN and volatility properties of submicron atmospheric aerosol in a boreal forest environment during the summer of 20102014Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, nr 9, s. 4733-4748Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A Volatility-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) was applied to study the hygroscopicity and volatility properties of submicron atmospheric aerosol particles in a boreal forest environment in Hyytiala, Finland during the summer of 2010. Aitken and accumulation mode internally mixed particles (50 nm, 75 nm and 110 nm in diameter) were investigated. Hygroscopicity was found to increase with particle size. The relative mass fraction of organics and SO42- is probably the major contributor to the fluctuation of the hygroscopicity for all particle sizes. The Cloud Condensation Nuclei Counter (CCNC)-derived hygroscopicity parameter kappa was observed to be slightly higher than kappa calculated from VH-TDMA data under sub-saturated conditions, potential reasons for this behavior are discussed shortly. Also, the size-resolved volatility properties of particles were investigated. Upon heating, more small particles evaporated compared to large particles. There was a significant amount of aerosol volume (non-volatile material) left, even at heating temperatures of 280 degrees C. Using size resolved volatility-hygroscopicity analysis, we concluded that there was always hygroscopic material remaining in the particles at different heating temperatures, even at 280 degrees C. This indicates that the observed non-volatile aerosol material did not consist solely of black carbon.

  • 267.
    Horst, Axel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Thornton, Brett F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Holmstrand, Henry
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Andersson, Per
    Crill, Patrick M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Stable bromine isotopic composition of atmospheric CH3Br2013Inngår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, s. 21040-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tropospheric methyl bromide (CH3Br) is the largest source of bromine to the stratosphere and plays an important role in ozone depletion. Here, the first stable bromine isotope composition (delta Br-81) of atmospheric CH3Br is presented. The delta Br-81 of higher concentration Stockholm samples and free air subarctic Abisko samples suggest a source/background value of -0.04 +/- 0.28 parts per thousand ranging up to +1.75 +/- 0.12 parts per thousand. The Stockholm delta Br-81 versus concentration relationship corresponds to an apparent isotope enrichment factor of -4.7 +/- 3.7 parts per thousand, representing the combined reaction sink. This study demonstrates the scientific potential of atmospheric delta Br-81 measurements, which in the future may be combined with other isotope systems in a top-down inverse approach to further understand key source and sink processes of methyl bromide.

  • 268. Huang, Kaicheng
    et al.
    Yi, Chuixiang
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). City University of New York, USA.
    Wu, Donghai
    Zhou, Tao
    Zhao, Xiang
    Blanford, William J.
    Wei, Suhua
    Wu, Hao
    Ling, Du
    Li, Zheng
    Tipping point of a conifer forest ecosystem under severe drought2015Inngår i: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 10, nr 2, artikkel-id 024011Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Drought-induced tree mortality has recently received considerable attention. Questions have arisen over the necessary intensity and duration thresholds of droughts that are sufficient to trigger rapid forest declines. The values of such tipping points leading to forest declines due to drought are presently unknown. In this study, we have evaluated the potential relationship between the level of tree growth and concurrent drought conditions with data of the tree growth-related ring width index (RWI) of the two dominant conifer species (Pinus edulis and Pinus ponderosa) in the Southwestern United State  (SWUS) and the meteorological drought-related standardized precipitation evapotranspiration index (SPEI). In this effort, we determined the binned averages of RWI and the 11 month SPEI within the month of July within each bin of 30 of RWI in the range of 0–3000.Wefound a significant correlation between the binned averages of RWI and SPEI at the regional-scale under dryer conditions. The tipping point of forest declines to drought is predicted by the regression model as SPEItp = −1.64 and RWItp = 0, that is, persistence of the water deficit (11 month) with intensity of −1.64 leading to negligible growth for the conifer species. When climate conditions are wetter, the correlation between the binned averages ofRWI and SPEI is weaker which we believe is most likely due to soil water and atmospheric moisture levels no longer being the dominant factor limiting tree growth.Wealso illustrate a potential application of the derived tipping point (SPEItp = −1.64) through an examination of the 2002 extreme drought event in theSWUSconifer forest regions. Distinguished differences in remote-sensing based NDVI anomalies were found between the two regions partitioned by the derived tipping point.

  • 269. Huber, M.
    et al.
    Caballero, Rodrigo
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    The early Eocene equable climate problem revisited2011Inngår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 7, nr 2, s. 603-633Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The early Eocene quable climate problem, i.e. warm extratropical annual mean and above-freezing winter temperatures evidenced by proxy records, has remained as one of the great unsolved problems in paleoclimate. Recent progress in modeling and in paleoclimate proxy development provides an opportunity to revisit this problem to ascertain if the current generation of models can reproduce the past climate features without extensive modification. Here we have compiled early Eocene terrestrial temperature data and compared with climate model results using a consistent and rigorous methodology. We test the hypothesis that equable climates can be explained simply as a response to increased greenhouse gas forcing within the framework of the atmospheric component of the Community Climate System Model (version 3), a climate model in common use for predicting future climate change. We find that, with suitably large radiative forcing, the model and data are in general agreement for annual mean and cold month mean temperatures, and that the pattern of high latitude amplification recorded by proxies can be largely, but not perfectly, reproduced.

  • 270. Huck, P. E.
    et al.
    Bodeker, G. E.
    Kremser, S.
    McDonald, A. J.
    Rex, M.
    Struthers, Hamish
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM). Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Semi-empirical models for chlorine activation and ozone depletion in the Antarctic stratosphere: proof of concept2013Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, nr 6, s. 3237-3243Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two semi-empirical models were developed for the Antarctic stratosphere to relate the shift of species within total chlorine (Cl-y = HCl + ClONO2 + HOCl + 2 x Cl-2 + 2xCl(2)O(2) + ClO + Cl) into the active forms (here: ClOx = 2xCl(2)O(2) + ClO), and to relate the rate of ozone destruction to ClOx. These two models provide a fast and computationally inexpensive way to describe the inter- and intra-annual evolution of ClOx and ozone mass deficit (OMD) in the Antarctic spring. The models are based on the underlying physics/chemistry of the system and capture the key chemical and physical processes in the Antarctic stratosphere that determine the interaction between climate change and Antarctic ozone depletion. They were developed considering bulk effects of chemical mechanisms for the duration of the Antarctic vortex period and quantities averaged over the vortex area. The model equations were regressed against observations of daytime ClO and OMD providing a set of empirical fit coefficients. Both semi-empirical models are able to explain much of the intra-and inter-annual variability observed in daily ClOx and OMD time series. This proof-of-concept paper outlines the semi-empirical approach to describing the evolution of Antarctic chlorine activation and ozone depletion.

  • 271.
    Hugelius, Gustaf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Spatial upscaling using thematic maps: an analysis of uncertainties in permafrost soil carbon estimates2012Inngår i: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 26, s. GB2026-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Studies of periglacial regions confirm their importance in the global carbon (C) cycle, but estimates of ecosystem C storage or green-house gas fluxes from these remote areas are generally poorly constrained and quantitative estimates of upscaling uncertainties are lacking. In this study, a regional database describing soil organic carbon (SOC) storage in periglacial terrain (European Russian Arctic) was used to evaluate spatial upscaling from point measurements using thematic maps. The selection of classes for upscaling and the need for replication in soil sampling were statistically evaluated. Upscaling using a land cover classification and a soil map estimated SOC storage to 48.5 and 47.0 kg C m(-2), respectively with 95% confidence intervals (CI) within +/- 8%. When corrected for spatial errors in the LCC upscaling proxy, SOC was estimated to 46.5 kg C m(-2) with a 95% CI reflecting propagated variance from both natural variability and spatial errors of +/- 11%. Artificially decreasing the size of the database used for upscaling showed that relatively stable results could be achieved with lower replication in some upscaling classes. Decreased spatial resolution for upscaling from 30 m to 1 km had little impact on SOC estimates in this region, but classification accuracy was dramatically reduced and land cover classes show different, sometimes nonlinear, responses to scale. The methods and recommendations presented here can provide guidelines for any future study where point observations of a variable are upscaled using remotely sensed thematic maps or classifications and potential applications for circum-arctic studies are discussed. For future upscaling studies at large geographic scales, a priori determination of sample sizes and tests to insure unimodal and statistically independent samples are recommended. If these prerequisites are not fulfilled, classes may be merged or subdivided prior to upscaling.

  • 272.
    Hultgren, Kristoffer
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tomographic views of the middle atmosphere from a satellite platform2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The middle atmosphere is a very important part of the Earth system. Until recently, we did not realize the importance of the structure of this vaporous shell and of the fundamental role it plays in both creating and sustaining life on the planet. Thanks to the development and improvement of new sounding methods and techniques, our knowledge of the composition of the atmosphere has become more detailed than ever before. We have also learned how to reveal complex interactions between different species and how they react to the incoming solar radiation.

    The middle part of the Earth’s atmosphere serves as a host for the Polar Mesospheric Clouds. These clouds consist of a thin layer of water-ice particles, only exsisting during the summer months and only close to the poles. There are indications that the occurrence of Polar Mesospheric Clouds may be linked to climate change. It has been pointed out that the first sightings coincide with the industrial revolution. Satellite observations have shown that Polar Mesospheric Clouds have become brighter and possibly more widely distributed during the 20th century. The clouds might therefore be suited as indicators of the variability of the climate - a good reason for studying this night-shimmering phenomena. The clouds can also be used as a proxy for middle atmospheric dynamics. In order to fully utilize Polar Mesospheric Clouds as tracers for atmospheric variability and dynamics, we need to better understand their local properties.

    The Optical Spectrograph and Infra-Red Imager System (OSIRIS) is one of two instruments installed on the Odin satellite. The optical spectrograph of this instrument observes sunlight scattered by the atmosphere and thus the Polar Mesospheric Clouds. This thesis deals with a tomographic technique that can reconstruct both horizontal and vertical structures of the clouds by using observations from various angles of the atmospheric region. From this information, microphysical properties such as particle sizes and number densities are obtained.

    The tomographic technique presented in this thesis also provides a basis for a new satellite concept - MATS. The idea behind the MATS satellite mission is to analyze wave activity in the atmosphere over a wide range of spatial and temporal scales, based on the scientific heritage from Odin/OSIRIS and the tomographic algorithms presented in this thesis.

  • 273.
    Hultgren, Kristoffer
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Gumbel, Jorg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tomographic and spectral views on the lifecycle of polar mesospheric clouds from Odin/OSIRIS2014Inngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, nr 24, s. 14129-14143Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vertical and horizontal structures of Polar Mesospheric Clouds (PMC) have been recovered by tomographic retrieval from the OSIRIS instrument aboard the Odin satellite. The tomographic algorithm has been used to return local scattering coefficients at seven wavelengths in the ultraviolet. This spectral information is used to retrieve PMC particle sizes, number density, and ice mass density. While substantial horizontal variations are found, local vertical structures are overall consistent with the idea of a growth-sedimentation process leading to a visible cloud. Large numbers of small particles are present near the top of the observed cloud layer. Toward lower altitudes, particle sizes increase while particle number densities decrease. A close relationship is found between the distribution of local PMC scattering coefficient and ice mass density. The bottom of the cloud often features large particles with mode radii exceeding 70 nm that rain out of the cloud before sublimating. The number density of these large particles is small, and they do not contribute significantly to the overall cloud brightness. As a consequence, the presence of these large particles can be difficult to identify for remote sensing techniques that integrate over the entire cloud column. When it comes to deriving absolute values of particle mode radius and number density, there is a strong sensitivity to assumptions on the mathematical form of the particle size distribution. We see a continued strong need to resolve this issue by co-analysis of various remote sensing techniques and observation geometries.

  • 274.
    Hultgren, Kristoffer
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Gumbel, Jörg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tomographic and spectral views on the lifecycle of Polar Mesospheric Clouds from Odin/OSIRISInngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996Artikkel i tidsskrift (Fagfellevurdert)
  • 275.
    Hultgren, Kristoffer
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Gumbel, Jörg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Degenstein, Doug
    Bourassa, Adam
    Lloyd, Nick
    Stegman, Jacek
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    First simultaneous retrievals of horizontal and vertical structures of Polar Mesospheric Clouds from Odin/OSIRIS tomography2013Inngår i: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 104, s. 213-223Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Limb-scanning satellites can provide global information about the vertical structure of Polar Mesospheric Clouds. However, information about horizontal structures usually remains limited. In eighteen days during the northern hemisphere summers of 2010 and 2011, the Odin satellite was operated in a special mesospheric mode with short limb scans limited to the altitude range of Polar Mesospheric Clouds. For Odin's Optical Spectrograph and InfraRed Imager System (OSIRIS) this provides multiple views through a given cloud volume, which forms a basis for tomographic analyses of the vertical/horizontal cloud structures. Here we present an algorithm for a tomographic analysis of mesospheric clouds based on maximum probability techniques. We also present the first simultaneously retrieved vertical and horizontal Polar Mesospheric Cloud structures. The findings show that the tomographic algorithm is able to locate detailed structures such as tilts, stratifications, or holes that cannot be analyzed by other limb, nadir, or ground-based measurements. We find a mean peak altitude of the clouds to be 83.6 km. We identify horizontal patches down to sizes of 300 km, which corresponds to a horizontal resolution that is limited by the available number of limb scans.

  • 276.
    Håkansson, Måns
    Stockholms universitet.
    Winds, shear and turbulence in atmospheric observations and models2002Doktoravhandling, med artikler (Annet vitenskapelig)
  • 277.
    Hólm, Elías Valur
    Stockholms universitet, Naturvetenskapliga fakulteten.
    High-order numerical methods for advection in atmospheric models1994Doktoravhandling, med artikler (Annet vitenskapelig)
  • 278. Igel, Adele L.
    et al.
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Leck, Caroline
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Savre, Julien
    Sedlar, Joseph
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    The free troposphere as a potential source of arctic boundary layer aerosol particles2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 13, s. 7053-7060Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study investigates aerosol particle transport from the free troposphere to the boundary layer in the summertime high Arctic. Observations from the Arctic Summer Cloud Ocean Study field campaign show several occurrences of high aerosol particle concentrations above the boundary layer top. Large-eddy simulations suggest that when these enhanced aerosol concentrations are present, they can be an important source of aerosol particles for the boundary layer. Most particles are transported to the boundary layer by entrainment. However, it is found that mixed-phase stratocumulus clouds, which often extend into the inversion layer, also can mediate the transport of particles into the boundary layer by activation at cloud top and evaporation below cloud base. Finally, the simulations also suggest that aerosol properties at the surface sometimes may not be good indicators of aerosol properties in the cloud layer.

  • 279. Iizuka, Yoshinori
    et al.
    Karlin, Torbjorn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Hansson, Margareta
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Sulphate and chloride aerosols during Holocene and last glacial periods preserved in the Talos Dome Ice Core, a peripheral region of Antarctica2013Inngår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, s. 20197-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Antarctic ice cores preserve the record of past aerosols, an important proxy of past atmospheric chemistry. Here we present the aerosol compositions of sulphate and chloride particles in the Talos Dome (TD) ice core from the Holocene and Last Glacial Period. We find that the main salt types of both periods are NaCl, Na2SO4 and CaSO4, indicating that TD ice contains relatively abundant sea salt (NaCl) from marine primary particles. By evaluating the molar ratio of NaCl to Na2SO4, we show that about half of the sea salt does not undergo sulphatisation during late Holocene. Compared to in inland Antarctica, the lower sulphatisation rate at TD is probably due to relatively little contact between sea salt and sulphuric acid. This low contact rate can be related to a reduced time of reaction for marine-sourced aerosol before reaching TD and/or to a reduced post-depositional effect from the higher accumulation rate at TD. Many sulphate and chloride salts are adhered to silicate minerals. The ratio of sulphate-adhered mineral to particle mass and the corresponding ratio of chloride-adhered mineral both increase with increasing dust concentration. Also, the TD ice appears to contain Ca(NO3)(2) or CaCO3 particles, thus differing from aerosol compositions in inland Antarctica, and indicating the proximity of peripheral regions to marine aerosols.

  • 280. Iizuka, Yoshinori
    et al.
    Tsuchimoto, Akira
    Hoshina, Yu
    Sakurai, Toshimitsu
    Hansson, Margareta
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Karlin, Torbjörn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Fujita, Koji
    Nakazawa, Fumio
    Motoyama, Hideaki
    Fujita, Shuji
    The rates of sea salt sulfatization in the atmosphere and surface snow of inland Antarctica2012Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, s. D04308-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most of the aerosol particles present in the surface snow and ice of inland Antarctica come from primary sea salt (sodium chloride) and marine biological activity (methansulfonic and sulfuric acids). Melted water from surface snow, firn, and Holocene ice contains mainly sodium, chloride, and sulfate ions. Although it is well known that sea salt aerosols react rapidly with sulfuric acid, a process known as sulfatization, it is not known when this process takes place. In this research we undertake to measure the proportion of sea salt aerosols that undergo sulfatization in the atmosphere and surface snow, as opposed to deeper ice, in order to understand the suitability of sea salt aerosols as a proxy for past climates in deep ice cores. We directly measure the sulfatization rates in recently fallen snow (0-4 m in depth) collected at the Dome Fuji station, using X-ray dispersion spectroscopy to determine the constituent elements of soluble particles and computing the molar ratios of sodium chloride and sodium sulfate. We estimate that about 90% of the initial sea salt aerosols sulfatize as they are taken up by precipitation over Dome Fuji or in the snowpack within one year after being deposited on the ice sheet.

  • 281. Insel, Nadja
    et al.
    Poulsen, Christopher J.
    Sturm, Christophe
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Ehlers, Todd A.
    Climate controls on Andean precipitation delta O-18 interannual variability2013Inngår i: Journal of Geophysical Research: Atmospheres, ISSN 2169-897X, Vol. 118, nr 17, s. 9721-9742Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stable oxygen isotopic composition of precipitation (O-18(p)) is used as a proxy for modern and past atmospheric, biologic, and surface processes. Although the physical processes that fractionate O-18 in vapor are known, regional controls of O-18(p) are not well understood. Here we present results from a limited-domain general circulation model (REMOiso) to quantify regional controls on modern (1976-1999) interannual and spatial variations of O-18(p) across four Andean domains spanning 50 degrees latitude. Results are compared to observed O-18(p) from meteorological stations. Simulated annual amount-weighted mean O-18(p) ranges between -4 and -7 (0-5 degrees S), -8 and -20 (14 degrees S-26 degrees S), -4 and -8.5 (30 degrees S-35 degrees S), and -7 to -10 (45 degrees S-50 degrees S). Relationships between climate and O-18(p) on interannual timescale vary along the Andes and are tied to changes in precipitation and large-scale dynamics. In the northern Andes, interannual variations in O-18(p) are mainly associated with precipitation amounts driven by low-latitude sea surface temperature and Amazon Basin conditions. In the north central Andes, O-18(p) correlates with precipitation amount and wind trajectory, which is related to the position of the Bolivian High. In the south central Andes, O-18(p) variability is mainly influenced by precipitation amounts that are controlled by the position and strength of the westerlies. In the southern Andes, interannual O-18(p) variability is linked to the intensification and weakening of the South Pacific High. The regional climate-O-18(p) relationships are discussed in the context of pre-Quaternary sedimentary O-18 proxy records.

  • 282.
    Iqbal, Waheed
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Hannachi, Abdel
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Gritsun, Andrey
    Franzke, Christian L.
    Dynamical behavior of T21QG model and Unstable Periodic Orbits (UPOs)Manuskript (preprint) (Annet vitenskapelig)
  • 283.
    Iqbal, Waheed
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Finnish Meteorological Institute, Finland.
    Hannachi, Abdel
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Hirooka, Toshihiko
    Chafik, Léon
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Harada, Yayoi
    Troposphere-Stratosphere Dynamical Coupling in Regard to the North Atlantic Eddy-Driven Jet Variability2019Inngår i: Journal of the Meteorological Society of Japan, ISSN 0026-1165, Vol. 97, nr 3, s. 657-671Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For several decades, the interaction between the troposphere and the stratosphere has attracted the attention of climate scientists, not least for the benefit it has on understanding dynamical processes and predictability. This interaction has been revived recently in regard to downward disturbance propagation effects on tropospheric circulations. In the current study, we investigate such interactions over the North Atlantic region in relation to the eddy-driven jet stream. The atmospheric low-frequency variability in the winter over the North Atlantic sector is mainly associated with variations in the latitudinal positions of the North Atlantic eddy-driven jet stream. The Japanese Reanalysis JRA-55 data has been used to analyze the jet latitude statistics. The results reveal robust trimoclality of the North Atlantic jet reflecting the latitudinal (i.e., northern, central and southern) positions in agreement with other reanalysis products. 30 major Sudden Stratospheric Warming (SSW) events are analyzed in relation to the three modes or regimes of the eddy-driven jet. The frequency of occurrence of the eddy-driven jet to be in a specific latitudinal position is largely related to the wave amplitude. The stratospheric polar vortex experiences significant changes via upward wave propagation associated with the jet positions. It is found that when the jet is close to its central mode the wave propagation of zonal wave number 2 (WN2) from the troposphere to the stratosphere is significantly high. Eliassen-Palm (EP) fluxes from all waves and zonal wave number 1 (WN1) depict the deceleration of the stratospheric polar vortex for the eddy-driven jet with a latitudinal position close to the northern mode. Plumb wave activity variations originate mainly in the Atlantic sector depending on the North Atlantic eddy-driven jet states. These significant associations between preferred latitudinal positions of the North Atlantic eddy-driven jet and the stratospheric dynamics may be a source of predictability.

  • 284.
    Iqbal (وحید اقبال ), Waheed
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    On atmospheric low frequency variability, teleconnections and link to jet variability2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The atmosphere is a complex system with an infinite number of independent variables. The best approximations of the atmosphere are made using numerical models. The use of such models provides an invaluable tool for studying the atmospheric system. In the atmosphere, narrow bands of strong winds at upper levels, called jet streams, impact the underlying large-scale weather conditions. In this Ph.D. thesis, I have studied jet stream variability from reanalyses and climate models. The regional climate model RCA4 simulations over South Asia reveal a good agreement between model results and reanalysis for jet stream representation. Lateral boundary data sources are believed to contribute to discrepancies over the mountainous regions.

    Currently, the weather forecasts have an upper limit of around 10 days. The atmospheric variability between 10 to 40 days is known as low frequency variability (LFV). This Ph.D. thesis also examined the LFV from a non-linear perspective, which indicated the existence of multiple recurring atmospheric conditions. The North Atlantic eddy-driven jet, which explains a major part of the winter variability over the North Atlantic region, has three preferred latitudinal positions situated south, closest to, and north of its climatological mean position. These positions represent, respectively, Greenland blocking, a low-pressure system over the North Atlantic, and a high-pressure system over the North Atlantic. An improved representation of this jet is reported from CMIP5 GCMs. However, the existence of three preferred latitudinal positions remains a challenge for these models.

    The statistical properties of recurring atmospheric conditions can potentially enhance current weather and climate predictions. Techniques from dynamical system theory, like unstable periodic orbits, can be employed to reconstruct such statistical properties. This has been demonstrated, for the first time, in a three-level baroclinic model, of intermediate complexity, for the Northern Hemisphere winter.

    In the Northern Hemisphere winter, there are times when the stratosphere gets warmer due to upward propagation of heat fluxes from the troposphere. This type of situation triggers a major sudden stratospheric warming, resulting in the equatorward shift of the jet streams and yielding much colder than usual surface conditions over the extratropics. I have studied thirty such events from the Japanese reanalysis data in relation to the three preferred latitudinal positions of the North Atlantic eddy-driven jet. The probability of strong upward propagation from the troposphere is significantly higher for the central position of the North Atlantic eddy-driven jet. These findings can potentially improve the troposphere-stratosphere predictions.

  • 285.
    Jahnke, Annika
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Mayer, Philipp
    Broman, Dag
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    McLachlan, Michael S
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Possibilities and limitations of equilibrium sampling using polydimethylsiloxane in fish tissue.2009Inngår i: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 77, nr 6, s. 764-70Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polydimethylsiloxane (PDMS) has been used for passive equilibrium sampling in numerous abiotic environmental matrices. Recently, this approach was extended to lipid-rich tissue. This work investigated the possibilities and limitations of using PDMS thin-film extraction for in tissue equilibrium sampling in fish species of varying lipid content. Polychlorinated biphenyls (PCBs) were used as model lipophilic organic pollutants. PDMS thin-films were inserted in intact fish tissue for differing time periods (1h up to 1 week). The thin-films were then solvent-extracted and the extracts were analyzed using gas chromatography coupled to mass spectrometry. Whether equilibrium had been established was investigated either by using PDMS thin-films of multiple thicknesses (140-620 microm) or by assessing kinetics by means of time series. Equilibration was found to be rapid (i.e. in the range of hours) in lipid-rich fish whereas equilibrium was not achieved within one week in tissues with low or medium lipid content (i.e. up to 2% lipids). Regarding lipid-rich fish, the newly developed method was found to be sufficiently sensitive to determine equilibrium partitioning concentrations of PCBs in lipids of samples from the Baltic Sea, and it is a promising approach for any kind of fatty tissue.

  • 286.
    Janson, Robert
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Monoterpenes from the boreal coniferous forest: their role in atmospheric chemistry1992Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The goal of this work has been to increase our knowledge of the role of the monoteipenes emitted by the boreal coniferous forest in atmospheric chemical processes. To this end, measurements of air concentrations and emission rates have been made in forests of Scots pine (Pinus sylvestris) and Norwegian spruce (Picea abies) at 4 sites throughout Sweden, during the summers of 1989 and 1990. Sampling was done with Tenax absorption tubes and analysis by gas chromotography with ion trap detection. Emission experiments were done with the chamber technique.

    Alpha-pinene and A’-carene were found to be the most abundant terpenes emitted by and in the air of the forests. Daytime concentrations were on the order of 0.1-0.3 ppbv total terpenes in the forest and a factor of 2-3 lower above, while nighttime concentrations could reach up to 7 ppbv on calm nights. Emission rates normalized to temperature were seen to have both a diumality with maximum at midday, and a seasonality with maxima observed in early May and October and a summer maximum in June-July. It is suggested that the maxima depend on plant-physiological processes in spring and fall and needle growth rate during the summer. Also wet vegetation was seen to emit a greater amount and different composition of terpenes than dry vegetatioa The forest floor emission rate was about 30-40% of the crown emission in the pine forest and had a seasonality similar to the crown emission. The ground emission could not be explained by sources in the litter and vegetation alone, and it is suggested that the roots of the trees are also important. An average July rate of emission of 0.6±0.5 pg(gdw h)'1 (20°Q and an annual flux of 370±180 thousand tons VOC yr'1 was determined for the boreal forest of Sweden. This flux is less than half of previous estimates, and about 80% of the emission of anthropogenic hydrocarbons in Sweden.

    Model studies and a review of recent laboratory studies reported in the literature indicate that 8-40% of the oxidation products can be expected to contribute to the atmospheric aerosol. Knowledge is still too incomplete to determine an 03 production potential. A Onedimensional model of turbulent diffusion and chemistry was used to study the diurnal variations of the monoterpenes and 03. It was found that surface exchange and turbulent diffusion are the predominant factors governing the diurnal variation of the surface concentrations of these gases. The terpenes were seen to have a potential role as chemical sinks for 03 and N03 in the nighttime boundary layer, depending on the strength of the terpene emission rate and the stability of the boundary layer.

  • 287. Jasechko, S.
    et al.
    Lechler, A.
    Pausata, Francesco S. R.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Fawcett, P. J.
    Gleeson, T.
    Cendon, D. I.
    Galewsky, J.
    LeGrande, A. N.
    Risi, C.
    Sharp, Z. D.
    Welker, J. M.
    Werner, M.
    Yoshimura, K.
    Late-glacial to late-Holocene shifts in global precipitation delta O-182015Inngår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 11, nr 10, s. 1375-1393Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reconstructions of Quaternary climate are often based on the isotopic content of paleo-precipitation preserved in proxy records. While many paleo-precipitation isotope records are available, few studies have synthesized these dispersed records to explore spatial patterns of late-glacial precipitation delta O-18. Here we present a synthesis of 86 globally distributed groundwater (n = 59), cave calcite (n = 15) and ice core (n = 12) isotope records spanning the late-glacial (defined as similar to 50 000 to similar to 20 000 years ago) to the late-Holocene (within the past similar to 5000 years). We show that precipitation delta O-18 changes from the late-glacial to the late-Holocene range from -7.1% (delta O-18(late-Holocene) > delta O-18(late-glacial)) to + 1.7% (delta O-18(late-glacial) > delta O-18(late-Holocene)), with the majority (77 %) of records having lower late-glacial delta O-18 than late-Holocene delta O-18 values. High-magnitude, negative precipitation delta O-18 shifts are common at high latitudes, high altitudes and continental interiors (delta O-18(late-Holocene) > delta O-18(late-glacial) by more than 3 %). Conversely, low-magnitude, positive precipitation delta O-18 shifts are concentrated along tropical and subtropical coasts (delta O-18(late-glacial) > delta O-18(late-Holocene) by less than 2 %). Broad, global patterns of late-glacial to late-Holocene precipitation delta O-18 shifts suggest that stronger-than-modern isotopic distillation of air masses prevailed during the late-glacial, likely impacted by larger global temperature differences between the tropics and the poles. Further, to test how well general circulation models reproduce global precipitation delta O-18 shifts, we compiled simulated precipitation delta O-18 shifts from five isotope-enabled general circulation models simulated under recent and last glacial maximum climate states. Climate simulations generally show better intermodel and model-measurement agreement in temperate regions than in the tropics, highlighting a need for further research to better understand how inter-model spread in convective rainout, seawater delta O-18 and glacial topography parameterizations impact simulated precipitation delta O-18. Future research on paleo-precipitation delta O-18 records can use the global maps of measured and simulated late-glacial precipitation isotope compositions to target and prioritize field sites.

  • 288.
    Jelbring, Hans
    Stockholms universitet.
    Wind controlled climate1998Doktoravhandling, monografi (Annet vitenskapelig)
  • 289. Jensen, Mari F.
    et al.
    Nilsson, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Nisancioglu, Kerim H.
    The interaction between sea ice and salinity-dominated ocean circulation: implications for halocline stability and rapid changes of sea ice cover2016Inngår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 47, nr 9-10, s. 3301-3317Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Changes in the sea ice cover of the Nordic Seas have been proposed to play a key role for the dramatic temperature excursions associated with the Dansgaard-Oeschger events during the last glacial. In this study, we develop a simple conceptual model to examine how interactions between sea ice and oceanic heat and freshwater transports affect the stability of an upper-ocean halocline in a semi-enclosed basin. The model represents a sea ice covered and salinity stratified Nordic Seas, and consists of a sea ice component and a two-layer ocean. The sea ice thickness depends on the atmospheric energy fluxes as well as the ocean heat flux. We introduce a thickness-dependent sea ice export. Whether sea ice stabilizes or destabilizes against a freshwater perturbation is shown to depend on the representation of the diapycnal flow. In a system where the diapycnal flow increases with density differences, the sea ice acts as a positive feedback on a freshwater perturbation. If the diapycnal flow decreases with density differences, the sea ice acts as a negative feedback. However, both representations lead to a circulation that breaks down when the freshwater input at the surface is small. As a consequence, we get rapid changes in sea ice. In addition to low freshwater forcing, increasing deep-ocean temperatures promote instability and the disappearance of sea ice. Generally, the unstable state is reached before the vertical density difference disappears, and the temperature of the deep ocean do not need to increase as much as previously thought to provoke abrupt changes in sea ice.

  • 290. Joensson, Bror F.
    et al.
    Doos, Kristofer
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Myrberg, Kai
    Lundberg, Peter A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    A Lagrangian-trajectory study of a gradually mixed estuary2011Inngår i: Continental Shelf Research, ISSN 0278-4343, E-ISSN 1873-6955, Vol. 31, nr 17, s. 1811-1817Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When modelling is used for investigating estuarine systems, a choice generally has to be made between applying simple mass-balance considerations or using a process-resolving three-dimensional (3-D) numerical circulation model. In the present investigation of the Gulf of Finland, a gradually mixed estuary in the Baltic Sea, it is demonstrated how Lagrangian-trajectory analysis applied to the output from a 3-D model minimizes the disadvantages associated with both of the modelling techniques referred to above. This formalism made it possible to demonstrate that the main part of the Gulf is dominated by water originating from the Baltic proper, and that the most pronounced mixing with fresh water from the river Neva takes place over a limited zone in the inner part of the Gulf. Dynamical insights were furthermore obtained by using the Lagrangian formalism to construct overturning stream-functions for the two source waters.

  • 291.
    Johansson, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). SMHI - Sveriges meteorologiska och hydrologiska institut.
    Improving the understanding of cloud radiative heating2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Clouds play an essential role in regulating Earth’s radiation budget by reflecting and absorbing energy at different spectra. As they interact with radiation, they can radiatively heat or cool the adjacent atmosphere and the surface. This heating effect can have a strong implication for the circulation and can change the surface properties by, for example, melting sea ice. The lack of high-resolution global observations has previously been a limitation for our understanding of the vertical structure of cloud radiative heating, and for evaluating the cloud radiative effect in climate models. In this thesis, we will investigate and document cloud radiative heating derived from space-based observations. We will focus on two regions, the Arctic and the Tropics, where cloud radiative heating plays an important, but fundamentally different role.

    In the Tropics, radiative heating at high altitudes influences the large scale circulation. Stratiform, deep convective, and cirrus clouds have a strong radiative impact in the upper troposphere. We found while investigating the Indian monsoon, that thick stratiform clouds will radiatively heat the upper troposphere by more than 0.2 K/day when the monsoon is most intense during June, July and August. Deep convective clouds cause considerable heating in the middle troposphere and at the same time, cool the tropical tropopause layer (TTL). These two thick cloud types will also cool the surface during the monsoon, weakening the temperature gradient between land and ocean. During these months, cirrus clouds are frequently located inside the TTL. We further find that in the Tropics, the climate model, EC-Earth, can capture the seasonal variations in cloud radiative heating seen in the satellite observations. However, the model overestimates the radiative heating in the upper region  and underestimates them in the middle region of the troposphere. This dissimilarity is caused by unrealistic longwave heating and low cloud fraction in the upper and middle of the troposphere, respectively.

    Radiative heating from cirrus, located inside the TTL, is considered to play an important role in the mass transport from the troposphere to the stratosphere. This heating generates enough buoyancy so that the air can pass the barrier of zero net radiative heating. We find that high thin single-layer clouds can heat the upper troposphere by 0.07 K/day. If a thick cloud layer is present underneath, they will radiatively suppress the high cloud, causing it to cool the adjacent air instead. The optical depth and cloud top height of the underlying cloud are two crucial factors that radiatively impact the high cloud above.

    Warm moist air is regularly transported from the mid-latitudes into the Arctic by low- and high-pressure systems. As the moist air enters the Arctic, it increases the cloudiness and warms the surface. This surface heating has the potential to affect the ice cover months after the intrusion. We find that during extreme moist intrusions, the surface temperature in the Arctic can rise by more than 5 K during the winter months with an increase in cloudiness by up to 30% downstream from the intrusion. These extra clouds radiatively heat the lower part of the atmosphere and cool the middle part, affecting the stability of the Arctic atmosphere.

  • 292.
    Johansson, Erik
    et al.
    Swedish Meteorological and Hydrological Institute (SMHI), Sweden.
    Devasthale, A.
    L'Ecuyer, T.
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    The vertical structure of cloud radiative heating over the Indian subcontinent during summer monsoon2015Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, nr 20, s. 11557-11570Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Clouds forming during the summer monsoon over the Indian subcontinent affect its evolution through their radiative impact as well as the release of latent heat. While the latter is previously studied to some extent, comparatively little is known about the radiative impact of different cloud types and the vertical structure of their radiative heating/cooling effects. Therefore, the main aim of this study is to partly fill this knowledge gap by investigating and documenting the vertical distributions of the different cloud types associated with the Indian monsoon and their radiative heating/cooling using the active radar and lidar sensors on-board CloudSat and CALIPSO. The intraseasonal evolution of clouds from May to October is also investigated to understand pre-to-post monsoon transitioning of their radiative heating/cooling effects. The vertical structure of cloud radiative heating (CRH) follows the northward migration and retreat of the monsoon from May to October. Throughout this time period, stratiform clouds radiatively warm the middle troposphere and cool the upper troposphere by more than +/- 0.2 K day(-1) (after weighing by cloud fraction), with the largest impacts observed in June, July and August. During these months, the fraction of high thin cloud remains high in the tropical tropopause layer (TTL). Deep convective towers cause considerable radiative warming in the middle and upper troposphere, but strongly cool the base and inside of the TTL. This cooling is stronger during active (-1.23 K day(-1)) monsoon periods compared to break periods (-0.36 K day(-1)). The contrasting radiative warming effect of high clouds in the TTL is twice as largeduring active periods than in break periods. These results highlight the increasing importance of CRH with altitude, especially in the TTL. Stratiform (made up of alto- and nimbostratus clouds) and deep convection clouds radiatively cool the surface by approximately -100 and -400Wm(-2) respectively while warming the atmosphere radiatively by about 40 to 150Wm(-2). While the cooling at the surface induced by deep convection and stratiform clouds is largest during active periods of monsoon, the importance of stratiform clouds further increases during break periods. The contrasting CREs (cloud radiative effects) in the atmosphere and at surface, and during active and break periods, should have direct implications for the monsoonal circulation.

  • 293.
    Johansson, Erik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute (SMHI), Sweden.
    Devasthale, Abhay
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    L'Ecuyer, Tristan
    Response of the lower troposphere to moisture intrusions into the Arctic2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 5, s. 2527-2536Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water vapor intrusions (WVIs) explain a significant fraction of total moisture transport and its variability in the Arctic. WVIs can precondition the Arctic atmosphere for accelerated melting of sea ice through effects on surface longwave radiation. Using data from the NASA's A-Train convoy of satellites to estimate the response of the lower troposphere to WVIs into the Arctic, we show that WVIs are associated with a surface warming of up to 5.3K (3.3K) in winter and 2.3K (1.6K) in summer, when averaged over the entire Arctic Ocean. The intrusions also lead to additional cloud radiative heating of up to 0.15K/d via up to 30% increased cloudiness in the vertical and also cause a weakening of the stability in the lower troposphere. The lower tropospheric and surface warming during winter and spring highlights the importance of understanding contribution of preconditioning to accelerated ice melt in the Arctic.

  • 294.
    Johansson, Erik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Swedish Meteorological and Hydrological Institute, Sweden.
    Devasthale, Abhay
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Ekman, Annica M. L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    L'Ecuyer, Tristan
    Wyser, Klaus
    Vertical cloud radiative heating in the tropics: Confronting the EC-Earth model with satellite observationsManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Understanding the coupling of clouds to large-scale circulation is one of the grand challenges faced by the global climate community. In this context, realistically simulating the vertical structure of cloud radiative heating/cooling (CRH) is a key premise to understand these couplings using Earth system models. Here, we evaluate CRH in two versions of the European Community Earth System Model (EC-Earth) using retrievals derived from the combined radar and lidar data from the CloudSat and CALIPSO satellites. One model version is used with two different horizontal resolutions (high resolution and its standard counterpart, i.e. EC-Earth3P-HR and EC-Earth3P). The other model version, EC-Earth3, is the EC-Earth version used for the AMIP experiment for CMIP6 experiments. The study focuses on the tropical region and the vertical structure of CRH and cloud properties, as such an evaluation has not yet been carried out for EC-Earth. We begin by evaluating the large-scale intra-seasonal variability in CRH in the different model versions, followed by an investigation of the changes in CRH during different phases of the El Nino Southern Oscillation (ENSO), a process that dominates the interannual climate variability in the tropics.

    All versions of EC-Earth evaluated here generally capture both the intra-seasonal and meridional variability in CRH over the convectively active and stratocumulus regions, and the CRH during the positive and negative phases of ENSO. However, two key differences between all model simulations and satellite retrievals emerge. First, the magnitude of CRH over the convectively active zones is up to twice as large in the models compared to the satellite data. Further dissection of net CRH into its shortwave and longwave components reveals noticeable differences in their vertical structure. The shortwave component of the radiative heating is overestimated by all model versions in the lowermost troposphere and underestimated in the middle troposphere. These over- and underestimations of shortwave heating are partly compensated by an overestimation of longwave cooling in the lowermost troposphere and heating in the middle troposphere. The observed biases in CRH can be traced back to disagreements in the cloud amount and cloud water content. We observe no noticeable improvement in the simulation of CRH by purely increasing the horizontal resolution in the model.

  • 295. Jones, P. D.
    et al.
    Melvin, T. M.
    Harpham, C.
    Grudd, Håkan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Helama, S.
    Cool North European summers and possible links to explosive volcanic eruptions2013Inngår i: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, ISSN 2169-897X, Vol. 118, nr 12, s. 6259-6265Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Exactly dated tree-ring measurements such as ring width (TRW) and maximum latewood density (MXD), which are sensitive to summer temperatures, can provide possible routes to investigate the occurrence of hemispheric-wide cool summers that might be linked to explosive tropical volcanic eruptions. These measurements can provide much longer records than the instrumental period, enabling much longer periods to be assessed and offers the potential to look at much larger eruptions than recorded over the last 200years. This paper looks at TRW evidence from Northern Fennoscandia extending over the last 7500years, using two independently produced chronologies from northern Sweden and northern Finland. TRW is less responsive than MXD to cool summer temperatures, but MXD is only available for the last 2000years. Additionally, looking at a relatively small location, compared to the Northern Hemisphere average, adds considerable noise. Progress in this area is likely to be made by developing more millennial-long TRW series across northern high latitudes or being able to develop MXD series from the sub-fossil material, which comprises most of the samples prior to the last 1000years. The three most extreme negative values for the region for the last 2000years are 1601, 542, and 1837, although the latter is not extreme in a long instrumental record for the region. The most extreme year of all occurred in 330BC. Of the 20 most extreme negative years, nine occurred during the AD years with the remaining 11 occurring during the prior 5500years.

  • 296.
    Jonsson, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Modelling the middle atmosphere and its sensitivity to climate change2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The Earth's middle atmosphere at about 10-100 km has shown a substantial sensitivity to human activities. First, the ozone layer has been reduced since the the early 1980s due to man-made emissions of halogenated hydrocarbons. Second, the middle atmosphere has been identified as a region showing clear evidence of climate change due to increased emissions of greenhouse gases. While increased CO2 abundances are expected to lead to a warmer climate near the Earth's surface, observations show that the middle atmosphere has been cooling by up to 2-3 degrees per decade over the past few decades. This is partly due to CO2 increases and partly due to ozone depletion.

    Predicting the future development of the middle atmosphere is problematic because of strong feedbacks between temperature and ozone. Ozone absorbs solar ultraviolet radiation and thus warms middle atmosphere, and also, ozone chemistry is temperature dependent, so that temperature changes are modulated by ozone changes.

    This thesis examines the middle atmospheric response to a doubling of the atmospheric CO2 content using a coupled chemistry-climate model. The effects can be separated in the intrinsic CO2-induced radiative response, the radiative feedback through ozone changes and the response due to changes in the climate of the underlying atmosphere and surface. The results show, as expected, a substantial cooling throughout the middle atmosphere, mainly due to the radiative impact of the CO2 increase. Model simulations with and without coupled chemistry show that the ozone feedback reduces the temperature response by up to 40%. Further analyses show that the ozone changes are caused primarily by the temperature dependency of the reaction O+O2+M->O3+M. The impact of changes in the surface climate on the middle atmosphere is generally small. In particular, no noticeable change in upward propagating planetary wave flux from the lower atmosphere is found. The temperature response in the polar regions is non-robust and thus, for the model used here, polar ozone loss does not appear to be sensitive to climate change in the lower atmosphere as has been suggested recently. The large interannual variability in the polar regions suggests that simulations longer than 30 years will be necessary for further analysis of the effects in this region.

    The thesis also addresses the long-standing dilemma that models tend to underestimate the ozone concentration at altitudes 40-75 km, which has important implications for climate change studies in this region. A photochemical box model is used to examine the photochemical aspects of this problem. At 40-55 km, the model reproduces satellite observations to within 10%, thus showing a substantial reduction in the ozone deficit problem. At 60-75 km, however, the model underestimates the observations by up to 35%, suggesting a significant lack of understanding of the chemistry and radiation in this region.

  • 297. Josey, S. A.
    et al.
    Yu, L.
    Gulev, S.
    Jin, X.
    Tilinina, N.
    Barnier, B.
    Brodeau, Laurent
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Unexpected impacts of the Tropical Pacific array on reanalysis surface meteorology and heat fluxes2014Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, nr 17, s. 6213-6220Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Tropical Pacific mooring array has been a key component of the climate observing system since the early 1990s. We identify a pattern of strong near surface humidity anomalies, colocated with the array, in the widely used European Center for Medium Range Weather Forecasting Interim atmospheric reanalysis. The pattern generates large, previously unrecognized latent and net air-sea heat flux anomalies, up to 50 Wm−2 in the annual mean, in reanalysis derived data sets employed for climate studies (TropFlux) and ocean model forcing (the Drakkar Forcing Set). As a consequence, uncertainty in Tropical Pacific ocean heat uptake between the 1990s and early 2000s at the mooring sites is significant with mooring colocated differences in decadally averaged ocean heat uptake as large as 20 Wm−2. Furthermore, these results have major implications for the dual use of air-sea flux buoys as reference sites and sources of assimilation data that are discussed.

  • 298. Jung, Thomas
    et al.
    Gordon, Neil D.
    Bauer, Peter
    Bromwich, David H.
    Chevallier, Matthieu
    Day, Jonathan J.
    Dawson, Jackie
    Doblas-Reyes, Francisco
    Fairall, Christopher
    Goessling, Helge F.
    Holland, Marika
    Inoue, Jun
    Iversen, Trond
    Klebe, Stefanie
    Lemke, Peter
    Losch, Martin
    Makshtas, Alexander
    Mills, Brian
    Nurmi, Pertti
    Perovich, Donald
    Reid, Philip
    Renfrew, Ian A.
    Smith, Gregory
    Svensson, Gunilla
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tolstykh, Mikhail
    Yang, Qinghua
    ADVANCING POLAR PREDICTION CAPABILITIES ON DAILY TO SEASONAL TIME SCALES2016Inngår i: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 97, nr 9, s. 1631-+Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The polar regions have been attracting more and more attention in recent years, fueled by the perceptible impacts of anthropogenic climate change. Polar climate change provides new opportunities, such as shorter shipping routes between Europe and East Asia, but also new risks such as the potential for industrial accidents or emergencies in ice-covered seas. Here, it is argued that environmental prediction systems for the polar regions are less developed than elsewhere. There are many reasons for this situation, including the polar regions being (historically) lower priority, with fewer in situ observations, and with numerous local physical processes that are less well represented by models. By contrasting the relative importance of different physical processes in polar and lower latitudes, the need for a dedicated polar prediction effort is illustrated. Research priorities are identified that will help to advance environmental polar prediction capabilities. Examples include an improvement of the polar observing system; the use of coupled atmosphere-sea ice-ocean models, even for short-term prediction; and insight into polar-lower latitude linkages and their role for forecasting. Given the enormity of some of the challenges ahead, in a harsh and remote environment such as the polar regions, it is argued that rapid progress will only be possible with a coordinated international effort. More specifically, it is proposed to hold a Year of Polar Prediction (YOPP) from mid-2017 to mid-2019 in which the international research and operational forecasting communites will work together with stakeholders in a period of intensive observing: modeling, prediction, verification, user engagement, and educational activities.

  • 299.
    Jönsson, Bror
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Some Concepts of Estuarine Modeling2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    If an estuarine system is to be investigated using an oceanographic modeling approach, a decision must be made whether to use a simple and robust framework based on e.g. mass-balance considerations, or if a more advanced process-resolving three-dimensional (3-D) numerical model are necessary. Although the former are straightforward to apply, certain fundamental constraints must be fulfilled. 3-D modeling, even though requiring significant efforts to implement, generates an abundance of highly resolved data in time and space, which may lead to problems when attempting to specify the "representative state" of the system, a common goal in estuarine studies.

    In this thesis, different types of models suitable for investigating estuarine systems have been utilized in various settings. A mass-balance model was applied to investigate potential changes of water fluxes and salinities due to the restoration of a mangrove estuary in northern Colombia. Seiches, i.e. standing waves, in the Baltic Sea were simulated using a 2-D shallow-water model which showed that the dominating harmonic oscillation originates from a fjord seiche in the Gulf of Finland rather than being global. Another study pertaining to the Gulf of Finland used velocity-fields from a 3-D numerical model together with Lagrangian-trajectory analyses to investigate the mixing dynamics. The results showed that water from the Baltic proper is mixed with that from the river Neva over a limited zone in the inner parts of the Gulf. Lagrangian-trajectory analysis was finally also used as a tool to compare mass-balance and 3-D model results from the Gulf of Riga and the Bay of Gdansk, highlighting when and where each method is applicable.

    From the present thesis it can be concluded that the above described estuarine-modeling approaches not only require different levels of effort for their implementation, but also yield results of varying quality. If oceanographic aspects are to be taken into account within Integrated Coastal Zone Managment, which most likely should be the case, it is therefore important to decide as early as possible in the planning process which model to use, since this choice ultimately determines how much information about the physical processes characterizing the system the model can be expected to provide.

  • 300.
    Kalivitis, Nikos
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Stavroulas, I.
    Bougiatioti, A.
    Kouvarakis, G.
    Gagne, S.
    Manninen, H. E.
    Kulmala, M.
    Mihalopoulos, N.
    Night time enhanced atmospheric ion concentrations in the marine boundary layer2012Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, nr 8, s. 3627-3638Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Measurements of atmospheric ions in the size range 0.8-42 nm were conducted at the environmental research station of the University of Crete at Finokalia from April 2008 to April 2009 in the frame of the EUCAARI project. Both positive and negative atmospheric ions were found to have a clear annual cycle, with minimum concentrations in summer. Their concentrations were found to vary with the prevailing meteorology and the abundance of aerosol particles in the atmosphere. High concentrations of ions were observed during new particle formation events. There were 53 nucleation events recorded. It was found that under certain atmospheric conditions enhanced ion concentrations can be observed during night. Overall, 39 night-time events were observed, all of them observed for the negatively charged particles while only 21 were observed for the positively charged particles. Night-time enhanced ion concentrations were more frequent during spring and autumn and no such events were recorded from July to September. A strong anti-correlation was found between air ion concentrations, especially at cluster sizes (1.25-1.66 nm), and condensation and coagulation sinks. Enhanced ion concentrations at night were found to be more frequent when air masses had traveled over the island of Crete, indicating possible association with local biogenic sources.

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