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  • 151.
    Engvall, Ann-Christine
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Krejci, Radovan
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Ström, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Treffeisen, Renate
    Scheele, Rinus
    Hermansen, Ove
    Paatero, Jussi
    Changes in aerosol properties during spring-summer period in the Arctic troposphere2008Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 8, nr 3, s. 445-462Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The change in aerosol properties during the transition from the more polluted spring to the clean summer in the Arctic troposphere was studied. A six-year data set of observations from Ny-Ålesund on Svalbard, covering the months April through June, serve as the basis for the characterisation of this time period. In addition four-day-back trajectories were used to describe air mass histories. The observed transition in aerosol properties from an accumulation-mode dominated distribution to an Aitken-mode dominated distribution is discussed with respect to long-range transport and influences from natural and anthropogenic sources of aerosols and pertinent trace gases. Our study shows that the air-mass transport is an important factor modulating the physical and chemical properties observed. However, the air-mass transport cannot alone explain the annually repeated systematic and rather rapid change in aerosol properties, occurring within a limited time window of approximately 10 days. With a simplified phenomenological model, which delivers the nucleation potential for new-particle formation, we suggest that the rapid shift in aerosol microphysical properties between the Arctic spring and summer is mainly driven by the incoming solar radiation in concert with transport of precursor gases and changes in condensational sink.

  • 152.
    Erbes, Gerhard
    Stockholms universitet, Naturvetenskapliga fakulteten.
    A study of fine-scale atmospheric dynamics and numerical advection methods1994Doktoravhandling, med artikler (Annet vitenskapelig)
  • 153.
    Eriksson, Erik
    Stockholms högskola.
    Atmospheric transports of oceanic constituents in their circulation in nature.1959Doktoravhandling, med artikler (Annet vitenskapelig)
  • 154. Espy, P. J.
    et al.
    Ochoa Fernandez, S.
    Forkman, P.
    Murtagh, D.
    Stegman, Jacek
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    The role of the QBO in the inter-hemispheric coupling of summer mesospheric temperatures2011Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, nr 2, s. 495-502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Inter-hemispheric coupling between the polar summer mesosphere and planetary-wave activity in the extra-tropical winter stratosphere has recently been inferred using Polar Mesospheric Cloud (PMC) properties as a proxy for mesospheric temperature (Karlsson et al., 2007). Here we confirm these results using a ten-year time series of July mesospheric temperatures near 60 degrees N derived from the hydroxyl (OH) nightglow. In addition, we show that the time-lagged correlation between these summer mesospheric temperatures and the ECMWF winter stratospheric temperatures displays a strong Quasi-Biennial Oscillation (QBO). The sign and phase of the correlation is consistent with the QBO modulation of the extra-tropical stratospheric dynamics in the Southern Hemisphere via the Holton-Tan mechanism (Holton and Tan, 1980). This lends strength to the identification of synoptic and planetary waves as the driver of the inter-hemispheric coupling, and results in a strong QBO modulation of the polar summer mesospheric temperatures.

  • 155.
    Falahat, Saeed
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Nycander, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    On the Generation of Bottom - Trapped Internal Tides2015Inngår i: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 45, nr 2, s. 526-545Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interaction of the barotropic tide with bottom topography when the tidal frequency omega is smaller than the Coriolis frequency f is examined. The resulting waves are called bottom-trapped internal tides. The energy density associated with these waves is computed using linear wave theory and vertical normal-mode decomposition in an ocean of finite depth. The global calculation of the modal energy density is performed for the semidiurnal M-2 tidal constituent and the two major diurnal tidal constituents K-1 and O-1. An observationally based decay time scale of 3 days is then used to transform the energy density to energy flux in units of watts per square meter. The globally integrated energy fluxes are found to be 1.99 and 1.43GW for the K-1 and O-1 tidal constituents, respectively. For the M-2 tidal constituent, it is found to be 1.15 GW. The Pacific Ocean is found to be the most energetic basin for the bottom-trapped diurnal tides. Two regional estimates of the bottom-trapped energy flux are given for the Kuril Islands and the Arctic Ocean, in which the bottom-trapped waves play a role for the tidally induced vertical mixing. The results of this study can be incorporated into ocean general circulation models and coupled climate models to improve the parameterization of the vertical mixing induced by breaking of the internal tides.

  • 156.
    Falahat, Saeed
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Nycander, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Roquet, Fabien
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Thurnherr, Andreas M.
    Hibiya, Toshiyuki
    Comparison of calculated energy flux of internal tides with microstructure measurements2014Inngår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 66, s. 23240-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Vertical mixing caused by breaking of internal tides plays a major role in maintaining the deep-ocean stratification. This study compares observations of dissipation from microstructure measurements to calculations of the vertical energy flux from barotropic to internal tides, taking into account the temporal variation due to the spring-neap tidal cycle. The dissipation data originate from two surveys in the Brazil Basin Tracer Release Experiment (BBTRE), and one over the LArval Dispersal along the Deep East Pacific Rise (LADDER3), supplemented with a few stations above the North-Atlantic Ridge (GRAVILUCK) and in the western Pacific (IZU). A good correlation is found between logarithmic values of energy flux and local dissipation in BBTRE, suggesting that the theory is able to predict energy fluxes. For the LADDER3, the local dissipation is much smaller than the calculated energy flux, which is very likely due to the different topographic features of BBTRE and LADDER3. The East Pacific Rise consists of a few isolated seamounts, so that most of the internal wave energy can radiate away from the generation site, whereas the Brazil Basin is characterised by extended rough bathymetry, leading to a more local dissipation. The results from all four field surveys support the general conclusion that the fraction of the internal-tide energy flux that is dissipated locally is very different in different regions.

  • 157.
    Falahat, Saeed
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Nycander, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Roquet, Fabien
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Zarroug, Moundheur
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Global Calculation of Tidal Energy Conversion into Vertical Normal Modes2014Inngår i: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 44, nr 12, s. 3225-3244Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A direct calculation of the tidal generation of internal waves over the global ocean is presented. The calculation is based on a semianalytical model, assuming that the internal tide characteristic slope exceeds the bathymetric slope (subcritical slope) and the bathymetric height is small relative to the vertical scale of the wave, as well as that the horizontal tidal excursion is smaller than the horizontal topographic scale. The calculation is performed for the M-2 tidal constituent. In contrast to previous similar computations, the internal tide is projected onto vertical eigenmodes, which gives two advantages. First, the vertical density profile and the finite ocean depth are taken into account in a fully consistent way, in contrast to earlier work based on the WKB approximation. Nevertheless, the WKB-based total global conversion follows closely that obtained using the eigenmode decomposition in each of the latitudinal and vertical distributions. Second, the information about the distribution of the conversion energy over different vertical modes is valuable, since the lowest modes can propagate over long distances, while high modes are more likely to dissipate locally, near the generation site. It is found that the difference between the vertical distributions of the tidal conversion into the vertical modes is smaller for the case of very deep ocean than the shallow-ocean depth. The results of the present work pave the way for future work on the vertical and horizontal distribution of the mixing caused by internal tides.

  • 158. Faranda, Davide
    et al.
    Messori, Gabriele
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Alvarez-Castro, M. Carmen
    Yiou, Pascal
    Dynamical properties and extremes of Northern Hemisphere climate fields over the past 60 years2017Inngår i: Nonlinear processes in geophysics, ISSN 1023-5809, E-ISSN 1607-7946, Vol. 24, nr 4, s. 713-725Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Atmospheric dynamics are described by a set of partial differential equations yielding an infinite-dimensional phase space. However, the actual trajectories followed by the system appear to be constrained to a finite-dimensional phase space, i.e. a strange attractor. The dynamical properties of this attractor are difficult to determine due to the complex nature of atmospheric motions. A first step to simplify the problem is to focus on observables which affect - or are linked to phenomena which affect - human welfare and activities, such as sea-level pressure, 2m temperature, and precipitation frequency. We make use of recent advances in dynamical systems theory to estimate two instantaneous dynamical properties of the above fields for the Northern Hemisphere: local dimension and persistence. We then use these metrics to characterize the seasonality of the different fields and their interplay. We further analyse the large-scale anomaly patterns corresponding to phase-space extremes - namely time steps at which the fields display extremes in their instantaneous dynamical properties. The analysis is based on the NCEP/NCAR reanalysis data, over the period 1948-2013. The results show that (i) despite the high dimensionality of atmospheric dynamics, the Northern Hemisphere sea-level pressure and temperature fields can on average be described by roughly 20 degrees of freedom; (ii) the precipitation field has a higher dimensionality; and (iii) the seasonal forcing modulates the variability of the dynamical indicators and affects the occurrence of phase-space extremes. We further identify a number of robust correlations between the dynamical properties of the different variables.

  • 159.
    Fitch, Anna C.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Pacific Northwest National Laboratory, Washington, USA.
    An Improved Double-Gaussian Closure for the Subgrid Vertical Velocity Probability Distribution Function2019Inngår i: Journal of the Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 76, s. 285-304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The vertical velocity probability distribution function (PDF) is analyzed throughout the depth of the lower atmosphere, including the subcloud and cloud layers, in four large-eddy simulation (LES) cases of shallow cumulus and stratocumulus. Double-Gaussian PDF closures are examined to test their ability to represent a wide range of turbulence statistics, from stratocumulus cloud layers characterized by Gaussian turbulence to shallow cumulus cloud layers displaying strongly non-Gaussian turbulence statistics. While the majority of the model closures are found to perform well in the former case, the latter presents a considerable challenge. A new model closure is suggested that accounts for high skewness and kurtosis seen in shallow cumulus cloud layers. The well-established parabolic relationship between skewness and kurtosis is examined, with results in agreement with previous studies for the subcloud layer. In cumulus cloud layers, however, a modified relationship is necessary to improve performance. The new closure significantly improves the estimation of the vertical velocity PDF for shallow cumulus cloud layers, in addition to performing well for stratocumulus. In particular, the long updraft tail representing the bulk of cloudy points is much better represented and higher-order moments diagnosed from the PDF are also greatly improved. However, some deficiencies remain owing to fundamental limitations of representing highly non-Gaussian turbulence statistics with a double-Gaussian PDF.

  • 160. Forsström, S.
    et al.
    Isaksson, E.
    Skeie, R. B.
    Ström, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Pedersen, C. A.
    Hudson, S. R.
    Berntsen, T. K.
    Lihavainen, H.
    Godtliebsen, F.
    Gerland, S.
    Elemental carbon measurements in European Arctic snow packs2013Inngår i: Journal of Geophysical Research: Atmospheres, ISSN 2169-897X, Vol. 118, nr 24, s. 13614-13627Artikkel i tidsskrift (Fagfellevurdert)
  • 161. Fountoukis, C.
    et al.
    Riipinen, Ilona
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    van der Gon, H. A. C. Denier
    Charalampidis, P. E.
    Pilinis, C.
    Wiedensohler, A.
    O'Dowd, C.
    Putaud, J. P.
    Moerman, M.
    Pandis, S. N.
    Simulating ultrafine particle formation in Europe using a regional ctm: contribution of primary emissions versus secondary formation to aerosol number concentrations2012Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, nr 18, s. 8663-8677Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A three-dimensional regional chemical transport model (CTM) with detailed aerosol microphysics, PMCAMx-UF, was applied to the European domain to simulate the contribution of direct emissions and secondary formation to total particle number concentrations during May 2008. PMCAMx-UF uses the Dynamic Model for Aerosol Nucleation and the Two-Moment Aerosol Sectional (TOMAS) algorithm to track both aerosol number and mass concentration using a sectional approach. The model predicts nucleation events that occur over scales of hundreds up to thousands of kilometers especially over the Balkans and Southeast Europe. The model predictions were compared against measurements from 7 sites across Europe. The model reproduces more than 70% of the hourly concentrations of particles larger than 10 nm (N-10) within a factor of 2. About half of these particles are predicted to originate from nucleation in the lower troposphere. Regional nucleation is predicted to increase the total particle number concentration by approximately a factor of 3. For particles larger than 100 nm the effect varies from an increase of 20% in the eastern Mediterranean to a decrease of 20% in southern Spain and Portugal resulting in a small average increase of around 1% over the whole domain. Nucleation has a significant effect in the predicted N-50 levels (up to a factor of 2 increase) mainly in areas where there are condensable vapors to grow the particles to larger sizes. A semi-empirical ternary sulfuric acid-ammonia-water parameterization performs better than the activation or the kinetic parameterizations in reproducing the observations. Reducing emissions of ammonia and sulfur dioxide affects certain parts of the number size distribution.

  • 162. Frech, Michael
    et al.
    Samuelsson, Patrick
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Jochum, Anne
    Regional surface fluxes over the NOPEX area1998Inngår i: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 212-213, s. 155-171Artikkel i tidsskrift (Fagfellevurdert)
  • 163.
    Frey, Lena
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Aerosol-cloud-radiation interactions in global climate models2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Clouds can reflect, absorb and re-emit radiation, thereby inducing a cooling or warming effect on the climate. However, the response of clouds to a changing climate is highly uncertain and the representation of clouds in state-of-the-art climate models remains a key challenge for future climate projections. Factors contributing to this uncertainty include processes on the microphysical scale involving aerosol particles with the size of just a few nanometers to micrometers. This thesis focuses on the representation of aerosol-cloud-radiation interactions in global climate models. Using idealized experiments from a model-intercomparison project with different anthropogenic aerosol forcings, it was found that both sulfate and non-sulfate aerosols yield an increase in cloud albedo in five regions of subtropical marine stratocumulus clouds. The changes in cloud albedo in the models were driven by changes in the cloud droplet number concentration and liquid water content. Further, it was found that the microphysical coupling of underlying aerosol-cloud interactions in models seems to dominate on the monthly timescale in subtropical marine stratocumulus regions, which can not be confirmed in observations. Quantifying the effect of aerosols on cloud properties in observations remains challenging. In addition, comparisons with satellite retrievals and the global climate model NorESM showed that this model is not able to capture elevated aerosol above cloud, seen in observations in two regions of marine stratocumulus clouds. Sensitivity experiments revealed that the model is most sensitive to the aerosol emissions, convection and wet scavenging in terms of the vertical aerosol distribution. Finally, the representation of aerosol absorption in global climate models was investigated. It was found that most of the models underestimate absorption by aerosols in a focus domain in Asia. Sensitivity studies with NorESM give rise to variations that lie within the large inter-model diversity.

  • 164.
    Frey, Lena
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Bender, Frida A.-M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Svensson, Gunilla
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Cloud albedo changes in response to anthropogenic sulfate and non-sulfate forcings in CMIP5 models2017Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, nr 14, s. 9145-9162Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of different aerosol types on cloud albedo are analysed using the linear relation between total albedo and cloud fraction found on a monthly mean scale in regions of subtropical marine stratocumulus clouds and the influence of simulated aerosol variations on this relation. Model experiments from the Coupled Model Intercomparison Project phase 5 (CMIP5) are used to separately study the responses to increases in sulfate, non-sulfate and all anthropogenic aerosols. A cloud brightening on the month-to-month scale due to variability in the background aerosol is found to dominate even in the cases where anthropogenic aerosols are added. The aerosol composition is of importance for this cloud brightening, that is thereby region dependent. There is indication that absorbing aerosols to some extent counteract the cloud brightening but scene darkening with increasing aerosol burden is generally not supported, even in regions where absorbing aerosols dominate. Month-to-month cloud albedo variability also confirms the importance of liquid water content for cloud albedo. Regional, monthly mean cloud albedo is found to increase with the addition of anthropogenic aerosols and more so with sulfate than non-sulfate. Changes in cloud albedo between experiments are related to changes in cloud water content as well as droplet size distribution changes, so that models with large increases in liquid water path and/or cloud droplet number show large cloud albedo increases with increasing aerosol. However, no clear relation between model sensitivities to aerosol variations on the month-to-month scale and changes in cloud albedo due to changed aerosol burden is found.

  • 165. Friedman, Jonathan S.
    et al.
    Tepley, C. A.
    Raizada, S
    Zhou, Q. H.
    Hedin, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Delgado, R
    Potassium Doppler-resonance lidar for the study of the mesosphere and lower thermosphere at Arecibo Obsevatory2003Inngår i: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 65, s. 1411-1424Artikkel i tidsskrift (Fagfellevurdert)
  • 166. Friman, Mathias
    et al.
    Strandberg, Gustav
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Linköping University, Sweden; Swedish Meteorological and Hydrological Institute, Sweden, .
    Historical responsibility for climate change: science and the science-policy interface2014Inngår i: Wiley Interdisciplinary Reviews: Climate Change, ISSN 1757-7780, E-ISSN 1757-7799, Vol. 5, nr 3, s. 297-316Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Since 1990, the academic literature on historical responsibility (HR) for climate change has grown considerably. Over these years, the approaches to defining this responsibility have varied considerably. This article demonstrates how this variation can be explained by combining various defining aspects of historical contribution and responsibility. Scientific knowledge that takes for granted choices among defining aspects will likely become a basis for distrust within science, among negotiators under the United Nations Framework Convention on Climate Change (UNFCCC), and elsewhere. On the other hand, for various reasons, not all choices can be explicated at all times. In this article, we examine the full breadth of complexities involved in scientifically defining HR and discuss how these complexities have consequences for the science-policy interface concerning HR. To this end, we review and classify the academic literature on historical contributions to and responsibility for climate change into categories of defining aspects. One immediately policy-relevant conclusion emerges from this exercise: Coupled with negotiators' highly divergent understandings of historical responsibility, the sheer number of defining aspects makes it virtually impossible to offer scientific advice without creating distrust in certain parts of the policy circle. This conclusion suggests that scientific attempts to narrow the options for policymakers will have little chance of succeeding unless policymakers first negotiate a clearer framework for historical responsibility. For further resources related to this article, please visit the . Conflict of interest: The authors have declared no conflicts of interest for this article.

  • 167.
    Fristedt, Tim
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Motionally induced voltages in near-shore environments: stratified flows, hydraulics and turbulence2000Doktoravhandling, monografi (Annet vitenskapelig)
  • 168. Gabriel, Axel
    et al.
    Körnich, Heiner
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Lossow, Stefan
    Urban, Joachim
    Murtagh, Donal
    Zonal asymmetries in middle atmospheric ozone and water vapour derived from Odin satellite data 2001–20102011Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, s. 9865-9885Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stationary wave patterns in middle atmospheric ozone (O3) and water vapour (H2O) are an important factor in the atmospheric circulation, but there is a strong gap in diagnosing and understanding their configuration and origin. Based on Odin satellite data from 2001 to 2010 we investigate the stationary wave patterns in O3 and H2O as indicated by the seasonal long-term means of the zonally asymmetric components O3* = O3-[O3] and H2O* = H2O-[H2O] ([O3], [H2O]: zonal means). At mid- and polar latitudes we find a pronounced wave one pattern in both constituents. In the Northern Hemisphere, the wave patterns increase during autumn, maintain their strength during winter and decay during spring, with maximum amplitudes of about 10–20 % of the zonal mean values. During winter, the wave one in O3* shows a maximum over the North Pacific/Aleutians and a minimum over the North Atlantic/Northern Europe and a double-peak structure with enhanced amplitude in the lower and in the upper stratosphere. The wave one in H2O* extends from the lower stratosphere to the upper mesosphere with a westward shift in phase with increasing height including a jump in phase at upper stratosphere altitudes. In the Southern Hemisphere, similar wave patterns occur mainly during southern spring. By comparing the observed wave patterns in O3* and H2O* with a linear solution of a steady-state transport equation for a zonally asymmetric tracer component we find that these wave patterns are primarily due to zonally asymmetric transport by geostrophically balanced winds, which are derived from observed temperature profiles. In addition temperature-dependent photochemistry contributes substantially to the spatial structure of the wave pattern in O3* . Further influences, e.g., zonal asymmetries in eddy mixing processes, are discussed.

  • 169.
    Gallardo Klenner, Laura
    Stockholms universitet, Naturvetenskapliga fakulteten.
    Oxidized nitrogen in the troposphere: the role of lightning1996Doktoravhandling, med artikler (Annet vitenskapelig)
  • 170.
    Gao, Qiuju
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Marine biogenic polysaccharides as a potential source of aerosol in the high Arctic: Towards a link between marine biology and cloud formation2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Primary marine aerosol particles containing biogenic polymer microgels play a potential role for cloud formation in the pristine high Arctic summer. One of the major sources of the polymer gels in Arctic aerosol was suggested to be the surface water and more specifically, the surface microlayer (SML) of the open leads within the perennial sea ice as a result of bubble bursting at the air-sea interface.  Phytoplankton and/or ice algae are believed to be the main origins of the polymer gels. In this thesis, we examine the chemical composition of biogenic polymers, with focus on polysaccharides, in seawater and airborne aerosol particles collected during the Arctic Summer Cloud Ocean Study (ASCOS) in the summer of 2008. The main results and findings include:

    • A novel method using liquid chromatography coupling with tandem mass spectrometry was developed and applied for identification and quantification of polysaccharides.
    • The enrichment of polysaccharides in the SML was shown to be a common feature of the Arctic open leads. Rising bubbles and surface coagulation of polymers are the likely mechanism for the accumulation of polysaccharides at the SML.
    • The size dependencies of airborne polysaccharides on the travel-time since the last contact with the open sea are indicative of a submicron microgel source within the pack ice.  The similarity of polysaccharides composition observed between the ambient aerosol particles and those generated by in situ bubbling experiments confines the microgel source to the open leads.

    The demonstrated occurrence of polysaccharides in surface sea waters and in air, with surface-active and hygroscopic properties, has shown their potential to serve as cloud condensation nuclei and subsequently promote cloud-drop activation in the pristine high Arctic. Presumably this possibility may renew interest in the complex but fascinating interactions between marine biology, aerosol, clouds and climate.

  • 171.
    Gao, Qiuju
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Araia, Musie
    Leck, Caroline
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Emmer, Åsa
    Characterization of exopolysaccharides in marine colloids by capillary electrophoresis with indirect UV detection2010Inngår i: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 662, nr 2, s. 193-199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method was established using capillary electrophoresis with indirect UV detection for analysis of monosaccharides liberated from exopolysaccharides by acidic hydrolysis. Tangential flow filtration was used to isolate high molecular weight polysaccharides from seawater. The capillary electrophoresis method included the use of a background electrolyte consisting of 2,6-dimethoxyphenol and cetyltrimethylammonium bromide. Several neutral sugars commonly existing in marine polysaccharides were separated under optimized conditions. The relative standard deviations were between 1.3% and 2.3% for relative migration time and 1.3-2.5% for peak height. Detection limits (at S/N 3) were in the range of 27.2-47.8 mu M. The proposed approach was applied to the analysis of hydrolyzed colloidal polysaccharides in seawater collected from the Baltic Sea. Nanomolar levels of liberated monosaccharides in seawater samples can be detected by preconcentration up to 30,000 times.

  • 172.
    Gao, Qiuju
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Leck, Caroline
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Rauschenberg, Carlton
    Matrai, Patricia A.
    On the chemical dynamics of extracellular polysaccharides in the high Arctic surface microlayer2012Inngår i: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 8, nr 4, s. 401-418Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The surface microlayer (SML) represents a unique system of which the physicochemical characteristics may differ from those of the underlying subsurface seawater (SSW). Within the Arctic pack ice area, the SML has been characterized as enriched in small colloids of biological origin, resulting from extracellular polymeric secretions (EPS). During the Arctic Summer Cloud-Ocean Study (ASCOS) in August 2008, particulate and dissolved organic matter (POM, DOM) samples were collected and chemically characterized from the SML and the corresponding SSW at an open lead centered at 87.5° N and 5°E.  Total organic carbon was persistently enriched in the SML with a mean enrichment factor (EF) of 1.45 ± 0.41, whereas sporadic depletions of dissolved carbohydrates and amino acids were observed. Monosaccharide compositional analysis reveals that EPS in the Arctic lead was formed mainly of distinctive heteropolysaccharides, enriched in xylose, fucose and glucose. The mean concentrations of total hydrolysable neutral sugars in SSW were 94.9 ± 37.5 nM in high molecular weight (HMW) DOM and 64.4 ± 14.5 nM in POM. The enrichment of polysaccharides in the SML appeared to be a common feature, with EFs ranging from 1.7 to 7.0 for particulate polysaccharides and 3.5 to 12.1 for polysaccharides in the HMW DOM fraction. A calculated monosaccharide yield suggests that polymers in the HMW DOM fraction were scavenged, without substantial degradation, into the SML.  Bubble scavenging experiments showed that newly aggregated particles could be formed abiotically by coagulation of low molecular weight nanometer-sized gels. Experimentally-generated aerosol particles were enriched in polysaccharides by factors of 22-70, relative to the source seawater. We propose that bubble scavenging of surface-active polysaccharides was one of the possible mechanisms for the enrichment of polysaccharides in the SML.

  • 173.
    Garcia-Carreras, Luis
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Parker, D. J.
    Marsham, J. H.
    Rosenberg, P. D.
    Brooks, I. M.
    Lock, A. P.
    Marenco, F.
    McQuaid, J. B.
    Hobby, M.
    The Turbulent Structure and Diurnal Growth of the Saharan Atmospheric Boundary Layer2015Inngår i: Journal of Atmospheric Sciences, ISSN 0022-4928, E-ISSN 1520-0469, Vol. 72, nr 2, s. 693-713Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The turbulent structure and growth of the remote Saharan atmospheric boundary layer (ABL) is described with in situ radiosonde and aircraft measurements and a large-eddy simulation model. A month of radiosonde data from June 2011 provides a mean profile of the midday Saharan ABL, which is characterized by a well-mixed convective boundary layer, capped by a small temperature inversion (<1K) and a deep, near-neutral residual layer. The boundary layer depth varies by up to 100% over horizontal distances of a few kilometers due to turbulent processes alone. The distinctive vertical structure also leads to unique boundary layer processes, such as detrainment of the warmest plumes across the weak temperature inversion, which slows down the warming and growth of the convective boundary layer. As the boundary layer grows, overshooting plumes can also entrain free-tropospheric air into the residual layer, forming a second entrainment zone that acts to maintain the inversion above the convective boundary layer, thus slowing down boundary layer growth further. A single-column model is unable to accurately reproduce the evolution of the Saharan boundary layer, highlighting the difficulty of representing such processes in large-scale models. These boundary layer processes are special to the Sahara, and possibly hot, dry, desert environments in general, and have implications for the large-scale structure of the Saharan heat low. The growth of the boundary layer influences the vertical redistribution of moisture and dust, and the spatial coverage and duration of clouds, with large-scale dynamical and radiative implications.

  • 174. Genberg, J.
    et al.
    van der Gon, H. A. C. Denier
    Simpson, D.
    Swietlicki, E.
    Areskoug, Hans
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Beddows, D.
    Ceburnis, D.
    Fiebig, M.
    Hansson, Hans-Christen
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Harrison, R. M.
    Jennings, S. G.
    Saarikoski, S.
    Spindler, G.
    Visschedijk, A. J. H.
    Wiedensohler, A.
    Yttri, K. E.
    Bergström, R.
    Light-absorbing carbon in Europe - measurement and modelling, with a focus on residential wood combustion emissions2013Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, nr 17, s. 8719-8738Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The atmospheric concentration of elemental carbon (EC) in Europe during the six-year period 2005-2010 has been simulated with the EMEP MSC-W model. The model bias compared to EC measurements was less than 20% for most of the examined sites. The model results suggest that fossil fuel combustion is the dominant source of EC in most of Europe but that there are important contributions also from residential wood burning during the cold seasons and, during certain episodes, also from open biomass burning (wildfires and agricultural fires). The modelled contributions from open biomass fires to ground level concentrations of EC were small at the sites included in the present study, <3% of the long-term average of EC in PM10. The modelling of this EC source is subject to many uncertainties, and it was likely underestimated for some episodes. EC measurements and modelled EC were also compared to optical measurements of black carbon (BC). The relationships between EC and BC (as given by mass absorption cross section, MAC, values) differed widely between the sites, and the correlation between observed EC and BC is sometimes poor, making it difficult to compare results using the two techniques and limiting the comparability of BC measurements to model EC results. A new bottom-up emission inventory for carbonaceous aerosol from residential wood combustion has been applied. For some countries the new inventory has substantially different EC emissions compared to earlier estimates. For northern Europe the most significant changes are much lower emissions in Norway and higher emissions in neighbouring Sweden and Finland. For Norway and Sweden, comparisons to source-apportionment data from winter campaigns indicate that the new inventory may improve model-calculated EC from wood burning. Finally, three different model setups were tested with variable atmospheric lifetimes of EC in order to evaluate the model sensitivity to the assumptions regarding hygroscopicity and atmospheric ageing of EC. The standard ageing scheme leads to a rapid transformation of the emitted hydrophobic EC to hygroscopic particles, and generates similar results when assuming that all EC is aged at the point of emission. Assuming hydrophobic emissions and no ageing leads to higher EC concentrations. For the more remote sites, the observed EC concentration was in between the modelled EC using standard ageing and the scenario treating EC as hydrophobic. This could indicate too-rapid EC ageing in the model in relatively clean parts of the atmosphere.

  • 175.
    Gidhagen, Lars
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Emissions, dynamics and dispersion of particles in polluted air2004Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The main objective of this thesis is to yield information on how atmospheric fine and ultrafine particles are dispersed in populated areas. Quantitative information on emissions, transport and removal is needed to assess the health risks of inhalable particles. Most effort is dedicated to describe, on the local and urban scales, the distribution of ultrafine particles (and thereby also total number concentrations) originating from traffic emissions. A minor part addresses the dispersion of toxic particles of industrial origin, dispersed over regional scales. The importance of aerosol dynamics for the distribution of ultrafine particles is assessed by coupling a three-dimensional dispersion model to a monodisperse aerosol model. Meteorological forcing, sometimes in a complex geometry, is simulated by a CFD model on the local scale and by a weather forecast model on the larger scales.

    The principal result of the study is that particle number concentrations can, at least for Swedish conditions, be simulated and quantitatively assessed in urban models in a similar way as particle mass or gaseous pollutants. The variability of the emissions and the removal effects of coagulation and dry deposition are investigated. Vehicle emissions of particle number vary with a factor of two depending on ambient temperature, with higher concentrations during cold conditions. Other important factors that determine particle emissions are fleet composition, vehicle speed (especially for gasoline-fueled cars) and the dilution rate in the microenvironment where emissions take place. Coagulation affects particle number concentrations in highly polluted environments like car tunnels or street canyons under low wind speed conditions, while it is of less importance in the urban background (reduced number concentrations of a few percent, as compared to completely inert particles). Dry deposition is effective over the road surface, due to the velocities and turbulence produced by moving vehicles. Dry deposition also has significant effects on the urban background concentrations, reducing average levels with up to 20-30%. Dry deposition is also shown to be an important mechanism to remove fine particulate mass on the regional scale.

    Simulated particle number concentrations, based on emission factors determined for the local vehicle fleet and influenced by aerosol dynamic processes, are evaluated against measured concentrations for three different traffic microenvironments and also for the entire Stockholm area. Regional dispersion of arsenic in PM10 is assessed and model results compared to measurements in Central and Northern Chile.

  • 176. Gidhagen, Lars
    et al.
    Engardt, Magnuz
    Lovenheim, Boel
    Johansson, Christer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Modeling effects of climate change on air quality and population exposure in urban planning scenarios2012Inngår i: Advances in meteorology, ISSN 1687-9309, s. 240894-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We employ a nested system of global and regional climate models, linked to regional and urban air quality chemical transport models utilizing detailed inventories of present and future emissions, to study the relative impact of climate change and changing air pollutant emissions on air quality and population exposure in Stockholm, Sweden. We show that climate change only marginally affects air quality over the 20-year period studied. An exposure assessment reveals that the population of Stockholm can expect considerably lower NO2 exposure in the future, mainly due to reduced local NOx emissions. Ozone exposure will decrease only slightly, due to a combination of increased concentrations in the city centre and decreasing concentrations in the suburban areas. The increase in ozone concentration is a consequence of decreased local NOx emissions, which reduces the titration of the long-range transported ozone. Finally, we evaluate the consequences of a planned road transit project on future air quality in Stockholm. The construction of a very large bypass road (including one of the largest motorway road tunnels in Europe) will only marginally influence total population exposure, this since the improved air quality in the city centre will be complemented by deteriorated air quality in suburban, residential areas.

  • 177.
    Gidhagen, Lars
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Johansson, Christer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Langner, Joakim
    Olivares, Gustavo
    Simulation of NOx and ultrafine particles in a street canyon in Stockholm, Sweden2004Inngår i: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 38, nr 14Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A computational fluid dynamic (CFD) model has been used to assess the concentrations of NOx and particle number in a street canyon in Stockholm with a high traffic volume. Comparisons of a simulated 11-week long time series of NOx with measurements (both sides of the street, urban background excluded) show good agreement, especially if emissions are distributed to be three times higher along the side of the street where the traffic is uphill, as compared to the downhill side. The simulation of number concentrations of inert particles indicates a similar asymmetry in emissions.

    A month-long measurement of particle size distribution (7–450 nm) at street level indicates that the ratio of nucleation size mode particle (7–20 nm) to total particle number (7–450 nm) is decreasing for increased particle surface area. Given the strong dominance of the locally generated particles over the urban background, this is interpreted as a local change in the size distribution. The results of a monodisperse aerosol dynamic model, coupled to the CFD model that simulates also the turbulence generated by vehicle movements, show that coagulation and deposition may reduce total particle inside the canyon with approximately 30% during low wind speeds. Most of the removal occurs shortly after emission, before the particles reach the leeward curb-side. Losses between the leeward curb-side and other locations in the street, e.g. roof levels, is estimated to be smaller, less than 10%. Coagulation is the dominating removal process under low wind speed conditions and deposition for higher wind speeds, the summed removal being smaller for high wind velocities. Deposition is enhanced over the road surface due to the velocities generated by vehicle movements. Although coagulation and deposition removal is most effective on the smallest ultrafine particles, this effect is not sufficient to explain the observed change in size distribution. It is suggested that also the formation of particles in the exhaust plumes is influenced by a larger particle surface area in the ambient air.

  • 178. Giesler, Reiner
    et al.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Karlsson, Jan
    Lundin, Erik J.
    Lyon, Steve W.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Humborg, Christoph
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Spatiotemporal variations of pCO(2) and delta C-13-DIC in subarctic streams in northern Sweden2013Inngår i: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 27, nr 1, s. 176-186Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Current predictions of climate-related changes in high-latitude environments suggest major effects on the C export in streams and rivers. To what extent this will also affect the stream water CO2 concentrations is poorly understood. In this study we examined the spatiotemporal variation in partial pressure of CO2 (pCO(2)) and in stable isotopic composition of dissolved inorganic carbon (delta C-13-DIC) in subarctic streams in northern Sweden. The selected watersheds are characterized by large variations in high-latitude boreal forest and tundra and differences in bedrock. We found that all streams generally were supersaturated in pCO(2) with an average concentration of 850 mu atm. The variability in pCO(2) across streams was poorly related to vegetation cover, and carbonaceous bedrock influence was manifested in high DIC concentrations but not reflected in either stream pCO(2) or delta C-13-DIC. Stream water pCO(2) values were highest during winter base flow when we also observed the lowest delta C-13-DIC values, and this pattern is interpreted as a high contribution from CO2 from soil respiration. Summer base flow delta C-13-DIC values probably are more affected by in situ stream processes such as aquatic production/respiration and degassing. A challenge for further studies will be to disentangle the origin of stream water CO2 and quantify their relative importance.

  • 179.
    Glantz, Paul
    Stockholms universitet.
    Aerosol cloud interactions in the marine boundary layers2002Doktoravhandling, med artikler (Annet vitenskapelig)
  • 180. Goldner, A.
    et al.
    Huber, M.
    Caballero, Rodrigo
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Does Antarctic glaciation cool the world?2013Inngår i: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 9, nr 1, s. 173-189Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, we compare the simulated climatic impact of adding an Antarctic ice sheet (AIS) to the greenhouse world of the Eocene and removing the AIS from the modern world. The modern global mean surface temperature anomaly (Delta T) induced by Antarctic Glaciation depends on the background CO2 levels and ranges from -1.22 to -0.18 K. The Eocene Delta T is nearly constant at similar to-0.25 K. We calculate an climate sensitivity parameter S[Antarctica] which we define as Delta T divided by the change in effective radiative forcing (Delta Q(Antarctica)) which includes some fast feedbacks imposed by prescribing the glacial properties of Antarctica. The main difference between the modern and Eocene responses is that a negative cloud feedback warms much of the Earth's surface as a large AIS is introduced in the Eocene, whereas this cloud feedback is weakly positive and acts in combination with positive sea-ice feedbacks to enhance cooling introduced by adding an ice sheet in the modern. Because of the importance of cloud feedbacks in determining the final temperature sensitivity of the AIS, our results are likely to be model dependent. Nevertheless, these model results suggest that the effective radiative forcing and feedbacks induced by the AIS did not significantly decrease global mean surface temperature across the Eocene-Oligocene transition (EOT -34.1 to 33.6 Ma) and that other factors like declining atmospheric CO2 are more important for cooling across the EOT. The results illustrate that the efficacy of AIS forcing in the Eocene is not necessarily close to one and is likely to be model and state dependent. This implies that using EOT paleoclimate proxy data by itself to estimate climate sensitivity for future climate prediction requires climate models and consequently these estimates will have large uncertainty, largely due to uncertainties in modelling low clouds.

  • 181. Gollvik, Stefan
    Investigations of problems related to the choice of the initial state for numerical weather prediction models1982Doktoravhandling, med artikler (Annet vitenskapelig)
  • 182. Granat, Lennart
    Atmospheric wet deposition: aspects on areal and temporal variations in the concentration/deposition field1976Doktoravhandling, med artikler (Annet vitenskapelig)
  • 183.
    Granat, Lennart
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Engström, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Praveen, Siva
    Rodhe, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Light Absorbing Material ("Soot") in Rainwater and in aerosol particles in the Maldives2010Inngår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, s. D16307-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Simultaneous measurements of soot (absorbing material at 528 nm) and inorganic ions in aerosol and precipitation at the Maldives Climate Observatory Hanimaadhoo during the period May 2005 to February 2007 have made it possible to calculate the washout ratio (WR) of these components as a measure of how efficiently they are scavenged by precipitation. Based on air trajectories the data have been separated into days with polluted air arriving from the Indian subcontinent in a north-easterly sector during winter and clean monsoon days with southerly flow from the Indian Ocean. The average soot concentration was a factor of ten higher in the former situations.

    Despite considerable scatter for individual days a systematic pattern emerged when the WR for the different components were compared with each other. During the monsoon season the WR for soot was similar to that of sulphate and other fine mode aerosol components, indicating that soot containing particles in these situations were efficient as cloud condensation nuclei. The origin of the light absorbing material during the monsoon season is unclear. We speculate that light absorbing material from the tropical ocean surface could contribute to the concentration of "soot" during the monsoon season.

    During the polluted winter days, on the other hand, the WR for soot was 3 times smaller than that of sulphate. This indicates that, even after a travel time of several days, the soot containing particles from India have retained much of their hydrophobic property and that the soot must be mainly externally mixed. The low WR and the infrequent rain during this season probably contribute to extending the atmospheric lifetime of soot well beyond several days.

    Surprisingly high concentrations of non sea salt calcium were measured during the monsoon season, substantially higher than during the winter season. The origin of these high values might be long-range transport from the Australian or African continents. Another possibility might be exopolymer gels derived from the ocean surface micro-layer.

  • 184.
    Grantinger, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Ensemble Kalman filters in mesoscale limited-area numerical weather prediction2007Licentiatavhandling, monografi (Annet vitenskapelig)
  • 185. Graversen, Rune G.
    et al.
    Burtu, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Arctic amplification enhanced by latent energy transport of atmospheric planetary waves2016Inngår i: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 142, nr 698, s. 2046-2054Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The atmospheric northward energy transport plays a crucial role for the Arctic climate; this transport brings to the Arctic an amount of energy comparable to that provided directly by the sun. The transport is accomplished by atmospheric waves-for instance large-scale planetary waves and meso-scale cyclones-and the zonal-mean circulation. These different components of the energy transport impact the Arctic climate differently. A split of the transport into stationary and transient waves constitutes a traditional way of decomposing the transport. However this procedure does not take into account the transport accomplished separately by the planetary and synoptic-scale waves. Here a Fourier decomposition is applied, which decomposes the transport with respect to zonal wave numbers. Reanalysis and model data reveal that the planetary waves impact Arctic temperatures much more than do synoptic-scale waves. In addition the latent transport by these waves affects the Arctic climate more than does the dry-static part. Finally, the EC-Earth model suggests that changes of the energy transport over the twentyfirst century will contribute to Arctic warming, despite the fact that in this model the total energy transport to the Arctic will decrease. This apparent contradictory result is due to the cooling induced by a decrease of the dry-static transport by planetary waves being more than compensated for by a warming caused by the latent counterpart.

  • 186.
    Graversen, Rune G.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Langen, Peter L.
    Mauritsen, Thorsten
    Polar Amplification in CCSM4: Contributions from the Lapse Rate and Surface Albedo Feedbacks2014Inngår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 27, nr 12, s. 4433-4450Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A vertically nonuniform warming of the troposphere yields a lapse rate feedback by altering the infrared irradiance to space relative to that of a vertically uniform tropospheric warming. The lapse rate feedback is negative at low latitudes, as a result of moist convective processes, and positive at high latitudes, due to stable stratification conditions that effectively trap warming near the surface. It is shown that this feedback pattern leads to polar amplification of the temperature response induced by a radiative forcing. The results are obtained by suppressing the lapse rate feedback in the Community Climate System Model, version 4 (CCSM4). The lapse rate feedback accounts for 15% of the Arctic amplification and 20% of the amplification in the Antarctic region. The fraction of the amplification that can be attributed to the surface albedo feedback, associated with melting of snow and ice, is 40% in the Arctic and 65% in Antarctica. It is further found that the surface albedo and lapse rate feedbacks interact considerably at high latitudes to the extent that they cannot be considered independent feedback mechanisms at the global scale.

  • 187. Graversen, Rune G.
    et al.
    Mauritsen, Thorsten
    Drijfhout, Sybren
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Mårtensson, Sebastian
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Warm winds from the Pacific caused extensive Arctic sea-ice melt in summer 20072011Inngår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 36, nr 11-12, s. 2103-2112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During summer 2007 the Arctic sea-ice shrank to the lowest extent ever observed. The role of the atmospheric energy transport in this extreme melt event is explored using the state-of-the-art ERA-Interim reanalysis data. We find that in summer 2007 there was an anomalous atmospheric flow of warm and humid air into the region that suffered severe melt. This anomaly was larger than during any other year in the data (1989-2008). Convergence of the atmospheric energy transport over this area led to positive anomalies of the downward longwave radiation and turbulent fluxes. In the region that experienced unusual ice melt, the net anomaly of the surface fluxes provided enough extra energy to melt roughly one meter of ice during the melting season. When the ocean successively became ice-free, the surface-albedo decreased causing additional absorption of shortwave radiation, despite the fact that the downwelling solar radiation was smaller than average. We argue that the positive anomalies of net downward longwave radiation and turbulent fluxes played a key role in initiating the 2007 extreme ice melt, whereas the shortwave-radiation changes acted as an amplifying feedback mechanism in response to the melt.

  • 188.
    Graversen, Rune G.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Mauritsen, Thorsten
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Källén, Erland
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Svensson, Gunilla
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Vertical structure of recent Arctic warming2008Inngår i: Nature, ISSN 0028-0836, Vol. 451, nr 7174, s. 53-56Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Near-surface warming in the Arctic has been almost twice as large as the global average over recent decades1, 2, 3, 4, 5—a phenomenon that is known as the 'Arctic amplification'. The underlying causes of this temperature amplification remain uncertain. The reduction in snow and ice cover that has occurred over recent decades6, 7 may have played a role5, 8. Climate model experiments indicate that when global temperature rises, Arctic snow and ice cover retreats, causing excessive polar warming9, 10, 11. Reduction of the snow and ice cover causes albedo changes, and increased refreezing of sea ice during the cold season and decreases in sea-ice thickness both increase heat flux from the ocean to the atmosphere. Changes in oceanic and atmospheric circulation, as well as cloud cover, have also been proposed to cause Arctic temperature amplification12, 13, 14, 15, 16, 17. Here we examine the vertical structure of temperature change in the Arctic during the late twentieth century using reanalysis data. We find evidence for temperature amplification well above the surface. Snow and ice feedbacks cannot be the main cause of the warming aloft during the greater part of the year, because these feedbacks are expected to primarily affect temperatures in the lowermost part of the atmosphere, resulting in a pattern of warming that we only observe in spring. A significant proportion of the observed temperature amplification must therefore be explained by mechanisms that induce warming above the lowermost part of the atmosphere. We regress the Arctic temperature field on the atmospheric energy transport into the Arctic and find that, in the summer half-year, a significant proportion of the vertical structure of warming can be explained by changes in this variable. We conclude that changes in atmospheric heat transport may be an important cause of the recent Arctic temperature amplification.

  • 189.
    Graversen, Rune Grand
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    On the recent Arctic Warming2008Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The Arctic region attracts considerable scientific interest in these years. Some of the Earth's most pronounced signs of the recent climate change are found here. The summer sea-ice cover is shrinking at an alarming rate. At the same time the region warms faster than the rest of the globe.

    The sea-ice reduction implies an increase of solar-radiation absorption at the surface leading to warming which is expected to be larger at higher than at lower latitudes. It is therefore often assumed that the sea-ice reduction is a major cause of the observed Arctic temperature amplification. However, results presented in this thesis suggest that the snow and ice-albedo feedbacks are a contributing but not dominating mechanism behind the Arctic amplification. A coupled climate-model experiment with a doubling of the atmospheric CO2 concentration reveals a considerable Arctic surface-air-temperature amplification in a world without surface-albedo feedback. The amplification is only 8 % larger when this feedback is included. Instead the greenhouse effect associated with an increase of humidity and cloud cover over the Arctic seems to play a major role for the amplification.

    Reanalysis data, which are partly based on observations, show Arctic temperature amplification well above the surface in the troposphere. In the summer season, the amplification has its maximum at ~ 2 km height. These trends cannot be explained by the snow- and ice-albedo feedbacks which are expected to induce the largest amplification near the surface. Instead, a considerable part of the trends aloft can be linked to an increase of the atmospheric energy transport into the Arctic.

    A major topic of this thesis is the linkage between the mid-latitude circulation and the Arctic warming. It is suggested that the atmospheric meridional energy transport is an efficient indicator of this linkage.

  • 190.
    Graversen, Rune Grand
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Källén, Erland
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Körnich, Heiner
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Atmospheric mass-budget inconsistency in the ERA-40 reanalysis2007Inngår i: Quarterly Journal of the Royal Meteorological society, ISSN 0035-9009, Vol. 133, s. 673-680Artikkel i tidsskrift (Fagfellevurdert)
  • 191. Grisogono, Branko
    et al.
    Ström, Linda
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Small-scale variability in the coastal atmospheric boundary layer1998Inngår i: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 88, s. 23-46Artikkel i tidsskrift (Fagfellevurdert)
  • 192. Grisogono, Branko
    et al.
    Tjernström, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Thermal mesoscale circulations on the Baltic coast 2. Perturbation of surface parameters1996Inngår i: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 101, s. 18999-19012Artikkel i tidsskrift (Fagfellevurdert)
  • 193.
    Grythe, Henrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM). Norwegian Institute for Air Research (NILU), Norway; Finnish Meteorological Institute (FMI), Finland.
    Kristiansen, Nina I.
    Groot Zwaaftink, Christine D.
    Eckhardt, Sabine
    Ström, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Tunved, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Krejci, Radovan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM). University of Helsinki, Finland.
    Stohl, Andreas
    A new aerosol wet removal scheme for the Lagrangian particle model FLEXPART2017Inngår i: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, nr 4, s. 1447-1466Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new and more physically based treatment of how removal by precipitation is calculated by FLEXPART is introduced, to take into account more aspects of aerosol diversity. Also new, is the definition of clouds and cloud properties. Results from simulations show good agreement with observed atmospheric concentrations for distinctly different aerosols. Atmospheric lifetimes were found to vary from a few hours (large aerosol particles) up to a month (small non-soluble).

  • 194.
    Grythe, Henrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM). Norwegian Institute for Air Research (NILU), Norway; Finnish Meteorological Institute (FMI), Finland.
    Ström, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Krejci, Radovan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM). University of Helsinki, Finland.
    Quinn, P.
    Stohl, A.
    A review of sea-spray aerosol source functions using a large global set of sea salt aerosol concentration measurements2014Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, nr 3, s. 1277-1297Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sea-spray aerosols (SSA) are an important part of the climate system because of their effects on the global radiative budget - both directly as scatterers and absorbers of solar and terrestrial radiation, and indirectly as cloud condensation nuclei (CCN) influencing cloud formation, lifetime, and precipitation. In terms of their global mass, SSA have the largest uncertainty of all aerosols. In this study we review 21 SSA source functions from the literature, several of which are used in current climate models. In addition, we propose a new function. Even excluding outliers, the global annual SSA mass produced spans roughly 3-70 Pg yr(-1) for the different source functions, for particles with dry diameter D-p < 10 mu m, with relatively little interannual variability for a given function. The FLEXPART Lagrangian particle dispersion model was run in backward mode for a large global set of observed SSA concentrations, comprised of several station networks and ship cruise measurement campaigns. FLEXPART backward calculations produce gridded emission sensitivity fields, which can subsequently be multiplied with gridded SSA production fluxes in order to obtain modeled SSA concentrations. This allowed us to efficiently and simultaneously evaluate all 21 source functions against the measurements. Another advantage of this method is that source-region information on wind speed and sea surface temperatures (SSTs) could be stored and used for improving the SSA source function parameterizations. The best source functions reproduced as much as 70% of the observed SSA concentration variability at several stations, which is comparable with state of the art aerosol models. The main driver of SSA production is wind, and we found that the best fit to the observation data could be obtained when the SSA production is proportional to U-10(3.5), where U-10 is the source region averaged 10m wind speed. A strong influence of SST on SSA production, with higher temperatures leading to higher production, could be detected as well, although the underlying physical mechanisms of the SST influence remains unclear. Our new source function with wind speed and temperature dependence gives a global SSA production for particles smaller than D-p < 10 mu m of 9 Pg yr(-1), and is the best fit to the observed concentrations.

  • 195.
    Grythe, Henrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi. Finnish Meteorological Institute (FMI), Finland; Norwegian Institute for Air Research (NILU), Norway.
    Virkkula, A.
    Backman, J.
    Aalto, P.
    Väänänen, R.
    Petäjä, T.
    Kerminen, V.-M.
    Busetto, M.
    Lanconelli, C.
    Lupi, A.
    Vitale, V.
    Montaguti, S.
    Udisti, R.
    Becagli, S.
    Ogren, J. A.
    Kulmala, M.
    Long-term measurements of aerosol optical properties and modeled aerosol transport paths at Dome C, AntarcticaManuskript (preprint) (Annet vitenskapelig)
  • 196. Guineva, V
    et al.
    Witt, Georg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Gumbel, Jörg
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Khaplanov, Mikhail
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Werner, R
    Hedin, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Neichev, S
    Kirov, B
    Bankov, L
    Gramatikov, P
    Tashev, V
    Popov, M
    Hauglund, K
    Hansen, G
    Ilstad, J
    Wold, H
    Lyman-alpha Detector Designed for Rocket Measurements of the Direct Solar Radiation at 121.5 nm2007Inngår i: Bulgarian Journal of Physics, Vol. 3, s. 116-127Artikkel i tidsskrift (Fagfellevurdert)
  • 197.
    Gumbel, Jörg
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Hultgren, Kristoffer
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Mesospheric Airglow/Aerosol Tomography and Spectroscopy (MATS) - a satellite mission on mesospheric wavesManuskript (preprint) (Annet vitenskapelig)
  • 198.
    Gumbel, Jörg
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Megner, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Charged meteoric smoke as ice nuclei in the mesosphere. Part 1: A review of basic concepts2009Inngår i: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, nr 12, s. 1225-1235Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The role of meteoric smoke as condensation nuclei for mesospheric ice has recently been challenged by model simulations on the global transport of meteoric material. At the same time a considerable fraction of smoke particles is charged in the mesosphere. This has significant effects on nucleation processes as it can remove the Kelvin barrier. We suggest that in particular nucleation on negatively charged smoke is likely to be a dominant mechanism for mesospheric ice formation. This is in contrast to nucleation on positive ion clusters as the latter is largely hampered by efficient ion/electron recombination. Surprisingly, the large potential of nucleation on charged smoke has so far not been considered in mesospheric ice models. A challenging question concerns the fraction of mesospheric smoke that is actually charged. An improved understanding of mesospheric charging and nucleation will require laboratory experiments on nuclei in the transition regime between molecular and particulate sizes.

  • 199. Gunnarson, Björn E.
    Holocene climate and environmental fluctuations from subfossil pines in central Sweden2002Doktoravhandling, med artikler (Annet vitenskapelig)
  • 200.
    Gunnarson, Björn
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Linderholm, Hans W.
    Moberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Improving a tree-ring reconstruction from west-central Scandinavia: 900 years of warm-season temperatures2011Inngår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 36, nr 1-2, s. 97-108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dendroclimatological sampling of Scots pine (Pinus sylvestris L.) has been made in the province of Jamtland, in the west-central Scandinavian mountains, since the 1970s. The tree-ring width (TRW) chronology spans several thousand years and has been used to reconstruct June August temperatures back to 1632 BC. A maximum latewood density (MXD) dataset, covering the period AD 1107-1827 (with gap 1292-1315) was presented in the 1980s by Fritz Schweingruber. Here we combine these historical MXD data with recently collected MXD data covering AD 1292-2006 into a single reconstruction of April September temperatures for the period AD 1107 2006. Regional curve standardization (RCS) provides more low-frequency variability than non-RCS and stronger correlation with local seasonal temperatures (51% variance explained). The MXD chronology shows a stronger relationship with temperatures than the TRW data, but the two chronologies show similar multi-decadal variations back to AD 1500. According to the MXD chronology, the period since AD 1930 and around AD 1150-1200 were the warmest during the last 900 years. Due to large uncertainties in the early part of the combined MXD chronology, it is not possible to conclude which period was the warmest. More sampling of trees growing near the tree-line is needed to further improve the MXD chronology.

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