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  • 1. Aichner, Bernhard
    et al.
    Makhmudov, Zafar
    Rajabov, Iljomjon
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Pausata, Francesco S. R.
    Werner, Martin
    Heinecke, Liv
    Kuessner, Marie L.
    Feakins, Sarah J.
    Sachse, Dirk
    Mischke, Steffen
    Hydroclimate in the Pamirs Was Driven by Changes in Precipitation-Evaporation Seasonality Since the Last Glacial Period2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 23, p. 13972-13983Article in journal (Refereed)
    Abstract [en]

    The Central Asian Pamir Mountains (Pamirs) are a high-altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacial-interglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31-kyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. delta D values of terrestrial biomarkers showed insolation-driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive delta D shifts driven by changes in precipitation seasonality were observed at ca. 31-30, 28-26, and 17-14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitation-evaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant.

  • 2. An, Lu
    et al.
    Rignot, Eric
    Chauche, Nolwenn
    Holland, David M.
    Holland, Denise
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kane, Emily
    Wood, Michael
    Klaucke, Ingo
    Morlighem, Mathieu
    Velicogna, Isabella
    Weinrebe, Wilhelm
    Willis, Josh K.
    Bathymetry of Southeast Greenland From Oceans Melting Greenland (OMG) Data2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 11, p. 197-205Article in journal (Refereed)
    Abstract [en]

    Southeast Greenland has been a major participant in the ice sheet mass loss over the last several decades. Interpreting the evolution of glacier fronts requires information about their depth below sea level and ocean thermal forcing, which are incompletely known in the region. Here, we combine airborne gravity and multibeam echo sounding data from the National Aeronautics and Space Administration's Oceans Melting Greenland (OMG) mission with ocean probe and fishing boat depth data to reconstruct the bathymetry extending from the glacier margins to the edges of the continental shelf. We perform a three-dimensional inversion of the gravity data over water and merge the solution with a mass conservation reconstruction of bed topography over land. In contrast with other parts of Greenland, we find few deep troughs connecting the glaciers to the sources of warm Atlantic Water, amidst a relatively uniform, shallow (350 m) continental shelf. The deep channels include the Kangerlugssuaq, Sermilik, Gyldenlove, and Tingmiarmiut Troughs.

  • 3. Arndt, Jan Erik
    et al.
    Schenke, Hans Werner
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Nitsche, Frank O.
    Buys, Gwen
    Goleby, Bruce
    Rebesco, Michele
    Bohoyo, Fernando
    Hong, Jongkuk
    Black, Jenny
    Greku, Rudolf
    Udintsev, Gleb
    Barrios, Felipe
    Reynoso-Peralta, Walter
    Taisei, Morishita
    Wigley, Rochelle
    The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0-A new bathymetric compilation covering circum-Antarctic waters2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 12, p. 3111-3117Article in journal (Refereed)
    Abstract [en]

    The International Bathymetric Chart of the Southern Ocean (IBCSO) Version 1.0 is a new digital bathymetric model (DBM) portraying the seafloor of the circum-Antarctic waters south of 60 degrees S. IBCSO is a regional mapping project of the General Bathymetric Chart of the Oceans (GEBCO). The IBCSO Version 1.0 DBM has been compiled from all available bathymetric data collectively gathered by more than 30 institutions from 15 countries. These data include multibeam and single-beam echo soundings, digitized depths from nautical charts, regional bathymetric gridded compilations, and predicted bathymetry. Specific gridding techniques were applied to compile the DBM from the bathymetric data of different origin, spatial distribution, resolution, and quality. The IBCSO Version 1.0 DBM has a resolution of 500 x 500 m, based on a polar stereographic projection, and is publicly available together with a digital chart for printing from the project website (www.ibcso.org) and at .

  • 4. Ball, W. T.
    et al.
    Rozanov, E.
    Alsing, J.
    Marsh, D. R.
    Tummon, F.
    Mortlock, Daniel J.
    Stockholm University, Faculty of Science, Department of Astronomy. Imperial College London, UK.
    Kinnison, D.
    Haigh, J. D.
    The Upper Stratospheric Solar Cycle Ozone Response2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 3, p. 1831-1841Article in journal (Refereed)
    Abstract [en]

    The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1-10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent data-merging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere U-shaped spatial structure with lobes emanating from the tropics (5-10 hPa) to high altitudes at midlatitudes (1-3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASIC(v2) ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used. Plain Language Summary Changes in the output of the Sun are thought to influence surface weather and climate through a set of processes initiated by the enhancement of upper stratosphere (32-48 km) ozone. In order to understand and assess the solar impact on the climate system, it is important that models reproduce the observed solar signal. However, the recommended data set for comparison with climate models remains disputed. We use newly improved observed ozone composites to determine both why there is disagreement between composites and which is most likely to be correct. We find that artifact-corrected composites represent the response better than those based on SBUV data alone. Further, we identify a U-shaped spatial structure with lobes emanating from the tropics to high altitudes at midlatitudes. An idealized chemistry climate model experiment and simulations considering historical meteorological conditions both support this conclusion. The results are of benefit to satellite-instrument scientists and to those engaged in atmospheric and climate research using both observations and climate models. The results will be important for assessing the solar signal in currently active and future assessments of chemistry climate models (e.g., Chemistry-Climate Model Initiative). We recommend the BASICv2 ozone composite to best represent historical upper stratospheric variability.

  • 5. Basu, N. B.
    et al.
    Destouni, G.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Jawitz, J. W.
    Thompson, S. E.
    Loukinova, N. V.
    Darracq, A.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Zanardo, S.
    Yaeger, M.
    Sivapalan, M.
    Rinaldo, A.
    Rao, P. S. C.
    Nutrient loads exported from managed catchments reveal emergent biogeochemical stationarity2010In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, no L23404Article in journal (Refereed)
    Abstract [en]

    Complexity of heterogeneous catchments poses challenges in predicting biogeochemical responses to human alterations and stochastic hydro‐climatic drivers. Human interferences and climate change may have contributed to the demise of hydrologic stationarity, but our synthesis of a large body of observational data suggests that anthropogenic impacts have also resulted in the emergence of effective biogeochemical stationarity in managed catchments. Long‐term monitoring data from the Mississippi‐Atchafalaya River Basin (MARB) and the Baltic Sea Drainage Basin (BSDB) reveal that inter‐annual variations in loads (LT) for total‐N (TN) and total‐P (TP), exported from a catchment are dominantly controlled by discharge (QT) leading inevitably to temporal invariance of the annual, flow‐weighted concentration, = (LT/QT). Emergence of this consistent pattern across diverse managed catchments is attributed to the anthropogenic legacy of accumulated nutrient sources generating memory, similar to ubiquitously present sources for geogenic constituents that also exhibit a linear LTQT relationship. These responses are characteristic of transport‐limited systems. In contrast, in the absence of legacy sources in less‐managed catchments, values were highly variable and supply limited. We offer a theoretical explanation for the observed patterns at the event scale, and extend it to consider the stochastic nature of rainfall/flow patterns at annual scales. Our analysis suggests that: (1) expected inter‐annual variations in LT can be robustly predicted given discharge variations arising from hydro‐climatic or anthropogenic forcing, and (2) water‐quality problems in receiving inland and coastal waters would persist until the accumulated storages of nutrients have been substantially depleted. The finding has notable implications on catchment management to mitigate adverse water‐quality impacts, and on acceleration of global biogeochemical cycles.

  • 6. Beck, Lisa J.
    et al.
    Sarnela, Nina
    Junninen, Heikki
    Hoppe, Clara J. M.
    Garmash, Olga
    Bianchi, Federico
    Riva, Matthieu
    Rose, Clemence
    Peräkylä, Otso
    Wimmer, Daniela
    Kausiala, Oskari
    Jokinen, Tuija
    Ahonen, Lauri
    Mikkilä, Jyri
    Hakala, Jani
    He, Xu-Cheng
    Kontkanen, Jenni
    Wolf, Klara K. E.
    Cappelletti, David
    Mazzola, Mauro
    Traversi, Rita
    Petroselli, Chiara
    Viola, Angelo P.
    Vitale, Vito
    Lange, Robert
    Massling, Andreas
    Nøjgaard, Jakob K.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Karlsson, Linn
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Jang, Sehyun
    Lee, Kitack
    Vakkari, Ville
    Lampilahti, Janne
    Thakur, Roseline C.
    Leino, Katri
    Kangasluoma, Juha
    Duplissy, Ella-Maria
    Siivola, Erkki
    Marbouti, Marjan
    Tham, Yee Jun
    Saiz-Lopez, Alfonso
    Petäjä, Tuukka
    Ehn, Mikael
    Worsnop, Douglas R.
    Skov, Henrik
    Kulmala, Markku
    Kerminen, Veli-Matti
    Sipilä, Mikko
    Differing Mechanisms of New Particle Formation at Two Arctic Sites2021In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 4, article id e2020GL091334Article in journal (Refereed)
    Abstract [en]

    New particle formation in the Arctic atmosphere is an important source of aerosol particles. Understanding the processes of Arctic secondary aerosol formation is crucial due to their significant impact on cloud properties and therefore Arctic amplification. We observed the molecular formation of new particles from low-volatility vapors at two Arctic sites with differing surroundings. In Svalbard, sulfuric acid (SA) and methane sulfonic acid (MSA) contribute to the formation of secondary aerosol and to some extent to cloud condensation nuclei (CCN). This occurs via ion-induced nucleation of SA and NH3 and subsequent growth by mainly SA and MSA condensation during springtime and highly oxygenated organic molecules during summertime. By contrast, in an ice-covered region around Villum, we observed new particle formation driven by iodic acid but its concentration was insufficient to grow nucleated particles to CCN sizes. Our results provide new insight about sources and precursors of Arctic secondary aerosol particles.

  • 7.
    Berglund, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Döös, Kristofer
    Stockholm University, Faculty of Science, Department of Meteorology .
    Groeskamp, Sjoerd
    McDougall, Trevor
    North Atlantic Ocean Circulation and Related Exchange of Heat and Salt Between Water Masses2023In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 50, no 13, article id e2022GL100989Article in journal (Refereed)
    Abstract [en]

    The meridional transport of mass, heat, and salt in the North Atlantic Ocean is often described for separate regions and parts, but rarely are all components of the circulation followed at once. Lagrangian trajectories have here been used to divide the North Atlantic Ocean circulation into four different pathways. In the boundary between the Subpolar and Subtropical Gyres, we show that the northward flowing waters exchange heat and salt with the water originating from the subpolar regions. This subsurface water mass exchange takes place in the first 1,000 m and is a key piece of the puzzle of how the Atlantic Meridional Overturning Circulation transports heat and salt. Between 30 & DEG; and 60 & DEG;N the northward flowing water loses 8.8 Gg/s salt to the Subpolar Gyre and an equivalent loss of only 1.7 Gg/s to the atmosphere due to the net fresh water influx.

  • 8.
    Bulatovic, Ines
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Savre, Julien
    Ludwig‐Maximilians‐Universität, Germany.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Tampere University of Technology, Finland.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Aerosol Indirect Effects in Marine Stratocumulus: The Importance of Explicitly Predicting Cloud Droplet Activation2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 6, p. 3473-3481Article in journal (Refereed)
    Abstract [en]

    Climate models generally simulate a unidirectional, positive liquid water path (LWP) response to increasing aerosol number concentration. However, satellite observations and large-eddy simulations show that the LWP may either increase or decrease with increasing aerosol concentration, influencing the overall magnitude of the aerosol indirect effect (AIE). We use large-eddy simulation to investigate the LWP response of a marine stratocumulus cloud and its dependence on different parameterizations for obtaining cloud droplet number concentration (CDNC). The simulations confirm that the LWP response is not always positiveregardless of CDNC treatment. However, the AIE simulated with the model version with prescribed CDNC is almost 3 times larger compared to the version with prognostic CDNC. The reason is that the CDNC in the prognostic scheme varies in time due to supersaturation fluctuations, collection, and other microphysical processes. A substantial spread in simulated AIE may thus arise simply due to the CDNC treatment. Plain Language Summary Our poor understanding of aerosol-cloud-radiation interactions (aerosol indirect effects) results in a major uncertainty in estimates of anthropogenic aerosol forcing. In climate models, the cloud water response to an increased aerosol number concentration may be especially uncertain as models simplify, or do not account for, processes that affect the cloud droplet number concentration and the total amount of cloud water. In this study, we employ large-eddy simulation to explore how different model descriptions for obtaining the number concentration of cloud droplets influences the cloud water response of a marine stratocumulus cloud and thus the simulated aerosol indirect effect. Our simulations show a qualitatively similar cloud water response regardless of model description: the total amount of cloud water increases first and then decreases with increasing aerosol concentration. However, the simulated aerosol indirect effect is almost 3 times as large when the number concentration of cloud droplets is prescribed compared to when it is dependent on the calculated supersaturation and other microphysical processes such as collisions between cloud droplets. Our findings show that a relatively simple difference in the treatment of the number concentration of cloud droplets in climate models may result in a significant spread in the simulated aerosol indirect effect.

  • 9. Cesana, Grégory V.
    et al.
    Khadir, Théodore
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Chepfer, Hélène
    Chiriaco, Marjolaine
    Southern Ocean Solar Reflection Biases in CMIP6 Models Linked to Cloud Phase and Vertical Structure Representations2022In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 49, no 22, article id e2022GL099777Article in journal (Refereed)
    Abstract [en]

    Over the Southern Ocean (SO, 40°S–70°S), climate models have consistently underestimated solar reflection. Here we evaluate the relationship between cloud profiles, cloud phase and radiation over the SO in Coupled Model Intercomparison Project Phase 6 (CMIP6) models against Clouds and the Earth's Radiant Energy System and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations. We find that the lack of solar reflection is slightly improved in CMIP6 models compared to CMIP5's, attributable to a better representation of cloud fraction and phase. We show that clouds have a different vertical structure and radiative effect south and north of where the 0°C isotherm meets the surface (∼55°S). Although the models capture the greater vertical extent of clouds south of 55°S, they fail to reproduce the observed increase in solar reflection, which we pinpoint to cloud phase biases. Increasing CMIP6 supercooled liquid cloud opacity should help reduce their persistent shortwave biases.

  • 10. Chafik, L.
    et al.
    Hakkinen, S.
    England, M. H.
    Carton, J. A.
    Nigam, S.
    Ruiz-Barradas, A.
    Hannachi, Abdelwaheb
    Stockholm University, Faculty of Science, Department of Meteorology .
    Miller, L.
    Global linkages originating from decadal oceanic variability in the subpolar North Atlantic2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 20, p. 10909-10919Article in journal (Refereed)
    Abstract [en]

    The anomalous decadal warming of the subpolar North Atlantic Ocean (SPNA), and the northward spreading of this warm water, has been linked to rapid Arctic sea ice loss and more frequent cold European winters. Recently, variations in this heat transport have also been reported to covary with global warming slowdown/acceleration periods via a Pacific climate response. We here examine the role of SPNA temperature variability in this Atlantic-Pacific climate connectivity. We find that the evolution of ocean heat content anomalies from the subtropics to the subpolar region, likely due to ocean circulation changes, coincides with a basin-wide Atlantic warming/cooling. This induces an Atlantic-Pacific sea surface temperature seesaw, which in turn, strengthens/weakens the Walker circulation and amplifies the Pacific decadal variability that triggers pronounced global-scale atmospheric circulation anomalies. We conclude that the decadal oceanic variability in the SPNA is an essential component of the tropical interactions between the Atlantic and Pacific Oceans.

  • 11.
    Chafik, Léon
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rossby, T.
    Volume, Heat, and Freshwater Divergences in the Subpolar North Atlantic Suggest the Nordic Seas as Key to the State of the Meridional Overturning Circulation2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 9, p. 4799-4808Article in journal (Refereed)
    Abstract [en]

    The meridional overturning circulation (MOC) decreases rapidly in subpolar and Nordic regions where the warm upper layer loses its buoyancy due to intense heat loss, sinks, and flows south. The major volume loss of the upper limb of the MOC, similar to 9.6 Sv out of 18.4 +/- 3.4 Sv, occurs as subduction across the Iceland Basin and Irminger Sea while the major heat loss, 273 TW out of 395 +/- 74 TW is associated with the MOC branch that continues into the Nordic Seas where North Atlantic deep overflow water is produced. The 122 +/- 79 TW heat flux convergence in the subpolar gyre appears to be significantly larger than various estimates of heat loss to the atmosphere. Much of the 0.09 +/- 0.02 Sv freshwater divergence is presumably balanced by runoff from the Greenland shelf. These estimates suggest that the Nordic Seas, not the Labrador Sea, are key to the state of the MOC. Plain language summary The meridional overturning circulation is a two-dimensional view of the flow north of upper-ocean warm water and its return south as cold deep and intermediate water. But the actual pathways of warm-to-cold conversion are several and remarkably diverse: One branch continues into the Nordic Seas where very dense water is produced and eventually spills back into the deep North Atlantic, another branch weaves its way around the entire subpolar basin and the southern tip of Greenland to the Labrador Sea where intermediate water is formed, and the third branch is an overturning that takes place within the subpolar waters between Greenland and Scotland. Volumetrically, this is the largest branch, but in terms of heat loss the Nordic Seas, branch surrenders far more heat to the atmosphere than the other two combined. It thus plays the key role in maintaining a strong meridional overturning circulation.

  • 12.
    Chen, Hans W.
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Penn State University .
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Körnich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorological and Hydrological Institute.
    Chen, Deliang
    A robust mode of climate variability in the Arctic: The Barents Oscillation2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 11, p. 2856-2861Article in journal (Refereed)
    Abstract [en]

    The Barents Oscillation (BO) is an anomalous wintertime atmospheric circulation pattern in the Northern Hemisphere that has been linked to the meridional flow over the Nordic Seas. There are speculations that the BO has important implications for the Arctic climate; however, it has also been suggested that the pattern is an artifact of Empirical Orthogonal Function (EOF) analysis due to an eastward shift of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In this study, EOF analyses are performed to show that a robust pattern resembling the BO can be found during different time periods, even when the AO/NAO is relatively stationary. This BO has a high and stable temporal correlation with the geostrophic zonal wind over the Barents Sea, while the contribution from the AO/NAO is small. The surface air temperature anomalies over the Barents Sea are closely associated with this mode of climate variability.

  • 13. Chen, Jie
    et al.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kjellström, Erik
    Lu, Zhengyao
    Chen, Fahu
    The Contribution of Vegetation-Climate Feedback and Resultant Sea Ice Loss to Amplified Arctic Warming During the Mid-Holocene2022In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 49, no 18, article id e2022GL098816Article in journal (Refereed)
    Abstract [en]

    Understanding influence of vegetation on past temperature changes in the Arctic region would help isolate uncertainty and build understanding of its broader climate system, with implications for paleoclimate reconstructions and future climate change. Using an Earth system model EC-Earth, we conduct a series of simulations to investigate the impact of vegetation-climate feedback on the Arctic climate during the mid-Holocene. Results show Arctic greening induced by the warming resulting from stronger orbital forcing, further amplifies the Arctic warming. The increased vegetation contributes 0.33 degrees C of Arctic warming and 0.35 x 106 km2 of Arctic sea ice loss. Increased Arctic vegetation leads to reduced land surface albedo and increased evapotranspiration, both of which cause local warming in spring and summer. The resultant sea ice loss causes warming in the following seasons, with atmospheric circulation anomalies further amplifying the warming. Our results highlight the significant contribution of vegetation-climate feedback to Arctic climate under natural conditions.

  • 14. Chen, Kaiqi
    et al.
    Axelsson, Josefine
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Li, Jianping
    Wang, Lanning
    EC-Earth Simulations Reveal Enhanced Inter-Hemispheric Thermal Contrast During the Last Interglacial Further Intensified the Indian Monsoon2022In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 49, no 6, article id e2021GL094551Article in journal (Refereed)
    Abstract [en]

    Paleoclimate proxy data indicate a stronger Indian summer monsoon (ISM) during the Last Interglacial (LIG) than in the present day. This is largely attributed to orbital forcing induced high seasonal and latitudinal insolation anomalies in the Northern Hemisphere during LIG. According to the general circulation model EC-Earth3, the simulated ISM rainfall is increased by approximately 28% during the LIG compared to the pre-industrial period as a result of the orbital forcing and the amplified land-sea contrast due to both local and remote ocean feedbacks. Although the LIG is often portrayed as a potential analogue of future warmer climates, our study suggests that the enhanced inter-hemispheric thermal gradient during the LIG strengthened the ISM, in opposition to the observed weakening of ISM under present-day warming.

  • 15. Chen, Long
    et al.
    Zhang, Yanxu
    Jacob, Daniel J.
    Soerensen, Anne L.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Harvard University, USA.
    Fisher, Jenny A.
    Horowitz, Hannah M.
    Corbitt, Elizabeth S.
    Wang, Xuejun
    A decline in Arctic Ocean mercury suggested by differences in decadal trends of atmospheric mercury between the Arctic and northern midlatitudes2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 14, p. 6076-6083Article in journal (Refereed)
    Abstract [en]

    Atmospheric mercury (Hg) in the Arctic shows much weaker or insignificant annual declines relative to northern midlatitudes over the past decade (2000-2009) but with strong seasonality in trends. We use a global ocean-atmosphere model of Hg (GEOS-Chem) to simulate these observed trends and determine the driving environmental variables. The atmospheric decline at northern midlatitudes can largely be explained by decreasing North Atlantic oceanic evasion. The midlatitude atmospheric signal propagates to the Arctic but is countered by rapid Arctic warming and declining sea ice, which suppresses deposition and promotes oceanic evasion over the Arctic Ocean. The resulting simulation implies a decline of Hg in the Arctic surface ocean that we estimate to be -0.67%yr(-1) over the study period. Rapid Arctic warming and declining sea ice are projected for future decades and would drive a sustained decline in Arctic Ocean Hg, potentially alleviating the methylmercury exposure risk for northern populations.

  • 16.
    Colleoni, Florence
    et al.
    Joseph Fourier University, France.
    Krinner, Gerhard
    Joseph Fourier University, France.
    Jaobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Sensitivity of the Late Saalian (140 kyrs BP) and LGM (21 kyrs BP) Eurasian ice sheet surface mass balance to vegetation feedbacks2009In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36, article id L08704Article in journal (Refereed)
    Abstract [en]

    This work uses an atmospheric general circulation model (AGCM) asynchronously coupled to an equilibrium vegetation model to investigate whether vegetation feedbacks could be one of the reasons why the Late Saalian ice sheet (140 kyrs BP) in Eurasia was substantially larger than the Last Glacial Maximum (LGM, 21 kyrs BP) Eurasian ice sheet. The modeled vegetation changes induce a regional cooling for the Late Saalian while they cause a slight regional warming for LGM. As a result, ablation along the margins of the Late Saalian ice sheet is significantly reduced, leading to an increased surface mass balance, while there are no significant mass balance changes observed from vegetation feedbacks at LGM.

  • 17. D'Arrigo, Rosanne
    et al.
    Palmer, Jonathan
    Ummenhofer, Caroline C.
    Kyaw, Nyi Nyi
    Krusic, Paul
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Three centuries of Myanmar monsoon climate variability inferred from teak tree rings2011In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, p. L24705-Article in journal (Refereed)
    Abstract [en]

    Asian monsoon extremes critically impact much of the globe's population. Key gaps in our understanding of monsoon climate remain due to sparse coverage of paleoclimatic information, despite intensified recent efforts. Here we describe a ring width chronology of teak, one of the first high-resolution proxy records for the nation of Myanmar. Based on 29 samples from 20 living trees and spanning from 1613-2009, this record, from the Maingtha forest reserve north of Mandalay, helps fill a substantial gap in spatial coverage of paleoclimatic records for monsoon Asia. Teak growth is positively correlated with rainfall and Palmer Drought Severity Index variability over Myanmar, during and prior to the May-September monsoon season (e. g., r = 0.38 with Yangon rainfall, 0.001, n 68). Importantly, this record also correlates significantly with larger-scale climate indices, including core Indian rainfall (23 degrees N, 76 degrees E; a particularly sensitive index of the monsoon), and the El Nino-Southern Oscillation (ENSO). The teak ring width value following the so-called 1997-98 El Nino of the Century suggests that this was one of the most severe droughts in the past similar to 300 years in Myanmar. Evidence for past dry conditions inferred for Myanmar is consistent with tree-ring records of decadal megadroughts developed for Thailand and Vietnam. These results confirm the climate signature related to monsoon rainfall in the Myanmar teak record and the considerable potential for future development of climate-sensitive chronologies from Myanmar and the broader region of monsoon Asia.

  • 18. Datseris, George
    et al.
    Blanco, Joaquin
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hadas, Or
    Bony, Sadrine
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Kaspi, Yohai
    Stevens, Bjorn
    Minimal Recipes for Global Cloudiness2022In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 49, no 20, article id e2022GL099678Article in journal (Refereed)
    Abstract [en]

    Clouds are primary modulators of Earth's energy balance. It is thus important to understand the links connecting variabilities in cloudiness to variabilities in other state variables of the climate system, and also describe how these links would change in a changing climate. A conceptual model of global cloudiness can help elucidate these points. In this work we derive simple representations of cloudiness, that can be useful in creating a theory of global cloudiness. These representations illustrate how both spatial and temporal variability of cloudiness can be expressed in terms of basic state variables. Specifically, cloud albedo is captured by a nonlinear combination of pressure velocity and a measure of the low-level stability, and cloud longwave effect is captured by surface temperature, pressure velocity, and standard deviation of pressure velocity. We conclude with a short discussion on the usefulness of this work in the context of global warming response studies.

  • 19. Dawkins, E. C. M.
    et al.
    Plane, J. M. C.
    Chipperfield, M. P.
    Feng, W.
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hedin, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Höffner, J.
    Friedman, J. S.
    First global observations of the mesospheric potassium layer2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 15, p. 5653-5661Article in journal (Refereed)
    Abstract [en]

    Metal species, produced by meteoric ablation, act as useful tracers of upper atmosphere dynamics and chemistry. Of these meteoric metals, K is an enigma: at extratropical latitudes, limited available lidar data show that the K layer displays a semiannual seasonal variability, rather than the annual pattern seen in other metals such as Na and Fe. Here we present the first near-global K retrieval, where K atom number density profiles are derived from dayglow measurements made by the Optical Spectrograph and Infrared Imager System spectrometer on board the Odin satellite. This robust retrieval produces density profiles with typical layer peak errors of 15% and a 2km vertical grid resolution. We demonstrate that these retrieved profiles compare well with available lidar data and show for the first time that the unusual semiannual behavior is near-global in extent. This new data set has wider applications for improving understanding of the K chemistry and of related upper atmosphere processes.

  • 20.
    De Boer, Agatha M.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hogg, Andrew McC.
    Control of the glacial carbon budget by topographically induced mixing2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 12, p. 4277-4284Article in journal (Refereed)
    Abstract [en]

    Evidence for the oceanic uptake of atmospheric CO2 during glaciations suggests that there was less production of southern origin deep water but, paradoxically, a larger volume of southern origin water than today. Here we demonstrate, using a theoretical box model, that the inverse relationship between volume and production rate of this water mass can be explained by invoking mixing rates in the deep ocean that are proportional to topographic outcropping area scaled with ocean floor slope. Furthermore, we show that the resulting profile, of a near-linear decrease in mixing intensity away from the bottom, generates a positive feedback on CO2 uptake that can initiate a glacial cycle. The results point to the importance of using topography-dependent mixing when studying the large-scale ocean circulation, especially in the paleo-intercomparison models that have failed to produce the weaker and more voluminous bottom water of the Last Glacial Maximum.

  • 21.
    Destouni, Georgia
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Asokan, Shilpa M.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jarsjö, Jerker
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Inland hydro-climatic interaction: Effects of human water use on regional climate2010In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, no 18, p. L18402-Article in journal (Refereed)
    Abstract [en]

    This study has quantified the regional evaporation and evapotranspiration changes, and the associated latent heat flux and surface temperature changes in the Central Asian region of the Aral Sea drainage basin and the Aral Sea itself from the pre-1950 period of the 20th century to 1983-2002. The human water use for irrigation yielded an average regional cooling effect of -0.6 degrees C due to increased evapotranspiration and latent heat flux from the irrigated land. The runoff water diverted for irrigation was more than 80% of the pre-1950 runoff into the terminal Aral Sea, and was largely lost from the regional water system by the evapotranspiration increase. The Aral Sea shrank due to this water loss, resulting in decreased evaporation and latent heat flux from the pre-1950 Aral Sea area extent, with an average regional warming effect of 0.5 degrees C. In general, the endorheic (land-internal) runoff and relative consumptive use of irrigation water from that runoff determine the relative inland water area shrinkage, its warming effect, and to what extent the warming counteracts the cooling effect of irrigation. Citation: Destouni, G., S. M. Asokan, and J. Jarsjo (2010), Inland hydro-climatic interaction: Effects of human water use on regional climate.

  • 22.
    Dey, Dipanjan
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Döös, Kristofer
    Stockholm University, Faculty of Science, Department of Meteorology .
    Atmospheric Freshwater Transport From the Atlantic to the Pacific Ocean: A Lagrangian Analysis2020In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 47, no 6, article id e2019GL086176Article in journal (Refereed)
    Abstract [en]

    The Atlantic-to-Pacific atmospheric freshwater transport was calculated using Lagrangian water mass trajectories. These were decomposed into eastward and westward moving classes, carrying water over Afro-Eurasia and over America, respectively. The results reveal that the midlatitude westerlies are contributing to midlatitude precipitation in the Pacific Ocean through transporting water mass from the midlatitude Atlantic Ocean over Afro-Eurasia. In addition, precipitation in the Eastern Tropical Pacific Ocean is found to be associated with the easterly winds carrying water mass from the tropical Atlantic Ocean. A quantitative analysis of the atmospheric freshwater transport furthermore shows that annually, the westerlies carry 0.40 Sv, approximately twice as much water as the easterly trade winds (0.26 Sv) to the Pacific Ocean, but with a strong seasonality. The Atlantic Ocean exports more freshwater across Afro-Eurasia than across America, except during the June-August periods. The average residence time of this atmospheric water transport is roughly twice as long when it crosses Afro-Eurasia (54 days) rather than America (24 days). Plain Language Summary The Pacific Ocean is less saline than the Atlantic Ocean. This salinity difference feeds the Conveyor Belt, which transfers warm water from the Pacific Ocean to the Atlantic as a shallow current and returns cold water from the Atlantic to the Pacific as a deep current that flows further south. One explanation of this salinity difference is that the evaporation dominates over precipitation in the Atlantic and vice versa for the Pacific. This salinity asymmetry has often been believed to be due to the westward directed winds carrying the moisture over America. However, in the present study we show that the moisture transport by the eastward directed winds over Afro-Eurasia is also important. The present study reveals that the moisture export from the midlatitude Atlantic to the midlatitude Pacific Ocean over Afro-Eurasia by the eastward directed winds is approximately twice as large as the moisture export from the tropical Atlantic Ocean to the Eastern Tropical Pacific Ocean across America by the westward directed winds, except during the June-August periods. The moisture carried over Afro-Eurasia by the eastward directed winds from the Atlantic to the Pacific Ocean tends to take place at higher altitude and remains longer in the atmosphere than the moisture carried by the westward directed trade winds.

  • 23. Dikpati, Mausumi
    et al.
    Anderson, Jeffrey L.
    Mitra, Dhrubaditya
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Ensemble Kalman filter data assimilation in a Babcock-Leighton solar dynamo model: An observation system simulation experiment for reconstructing meridional flow speed2014In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 41, no 15, p. 5361-5369Article in journal (Refereed)
    Abstract [en]

    Accurate knowledge of time variation in meridional flow speed and profile is crucial for estimating the solar cycle's features, which are ultimately responsible for causing space climate variations. However, no consensus has been reached yet about the Sun's meridional circulation pattern observations and theories. By implementing an ensemble Kalman filter (EnKF) data assimilation in a Babcock-Leighton solar dynamo model using Data Assimilation Research Testbed framework, we find that the best reconstruction of time variation in meridional flow speed can be obtained when 10 or more observations are used with an updating time of 15 days and a 10% observational error. Increasing ensemble size from 16 to 160 improves reconstruction. Comparison of reconstructed flow speed with true state reveals that EnKF data assimilation is very powerful for reconstructing meridional flow speeds and suggests that it can be implemented for reconstructing spatiotemporal patterns of meridional circulation.

  • 24.
    do Carmo, J.B:
    et al.
    Univ Sao Paulo.
    Keller, M.
    USDA Forest Service.
    Dias, J.D.
    Univ Sao Paulo.
    de Carmago, P.B:
    Univ Sao Paulo.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    A source of methane from upland forests in the Brazilian Amazon.2006In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 33, no L04809Article in journal (Refereed)
    Abstract [en]

    We sampled air in the canopy layer of undisturbed upland forests during wet and dry seasons at three sites in the Brazilian Amazon region and found that both methane (CH4) and carbon dioxide (CO2) mixing ratios increased at night. Such increases were consistent across sites and seasons. A canopy layer budget model based on measured soil-atmosphere fluxes of CO2 was constructed to estimate ecosystem CH4 emission. We estimate that net CH4 emission in upland forests ranged from 2 to 21 mg CH4 m−2 d−1. While the origin of this CH4 source is unknown, these ground based measurements are consistent with recent findings based on satellite observations that indicate a large, unidentified source of CH4 in tropical forest regions.

  • 25. Douglas, Peter M. J.
    et al.
    Moguel, Regina Gonzalez
    Anthony, Katey M. Walter
    Wik, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Dawson, Katherine S.
    Smith, Derek A.
    Yanay, Ella
    Lloyd, Max K.
    Stolper, Daniel A.
    Eiler, John M.
    Sessions, Alex L.
    Clumped Isotopes Link Older Carbon Substrates With Slower Rates of Methanogenesis in Northern Lakes2020In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 47, no 6, article id e2019GL086756Article in journal (Refereed)
    Abstract [en]

    The release of long-stored carbon from thawed permafrost could fuel increased methanogenesis in northern lakes, but it remains unclear whether old carbon substrates released from permafrost are metabolized as rapidly by methanogenic microbial communities as recently produced organic carbon. Here, we apply methane (CH4) clumped isotope (Delta(18)) and C-14 measurements to test whether rates of methanogenesis are related to carbon substrate age. Results from culture experiments indicate that Delta(18) values are negatively correlated with CH4 production rate. Measurements of ebullition samples from thermokarst lakes in Alaska and glacial lakes in Sweden indicate strong negative correlations between CH4 Delta(18) and the fraction modern carbon. These correlations imply that CH4 derived from older carbon substrates is produced relatively slowly. Relative rates of methanogenesis, as inferred from Delta(18) values, are not positively correlated with CH4 flux estimates, highlighting the likely importance of environmental variables other than CH4 production rates in controlling ebullition fluxes. Plain Language Summary There is concern that carbon from thawed permafrost will be emitted to the atmosphere as methane (CH4). It is currently uncertain whether old organic carbon from thawed permafrost can be converted to CH4 as rapidly as organic carbon recently fixed by primary producers. We address this question by combining radiocarbon and clumped isotope measurements of CH4 from lakes in permafrost landscapes. Radiocarbon (C-14) measurements indicate the age of CH4 carbon sources. We present data from culture experiments that support the hypothesis that clumped isotope values are dependent on microbial CH4 production rate. In lake bubble samples, we observe a strong correlation between these two measurements, which implies that CH4 formed from older carbon is produced relatively slowly. We also find that higher rates of CH4 production, as inferred from clumped isotopes, are not linked to higher rates of CH4 emissions, implying that variables other than CH4 production rate strongly influence emission rates.

  • 26.
    Eilola, K.
    et al.
    Swedish Meteorol & Hydrol Inst, S-60176 Norrköping, Sweden.
    Mårtensson, Sebastian
    Swedish Meteorol & Hydrol Inst, S-60176 Norrköping, Sweden.
    Meier, Markus
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish Meteorol & Hydrol Inst, S-60176 Norrköping, Sweden.
    Modeling the impact of reduced sea ice cover in future climate on the Baltic Sea biogeochemistry2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 1, p. 149-154Article in journal (Refereed)
    Abstract [en]

    In a warming future climate, the sea ice cover is expected to decrease, with very likely large consequences for the marine ecosystem. We investigated the impact of future sea ice retreat on the Baltic Sea biogeochemistry at the end of the century, using an ensemble of regionalized global climate simulations. We found that the spring bloom will start by up to one month earlier and winds and wave-induced resuspension will increase, causing an increased transport of nutrients from the productive coastal zone into the deeper areas. The internal nutrient fluxes do not necessarily increase because they also depend on oxygen and temperature conditions of the bottom water. Winter mixing increases in areas having reduced ice cover and in areas having reduced stratification due to increased freshwater supply. The reduced sea ice cover therefore partly counteracts eutrophication because increased vertical mixing improves oxygen conditions in lower layers.

  • 27.
    Ekman, Annica
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Engström, Anders
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    de Reus, Marian
    Max Planck Institute for Chemistry, Mainz, Germany.
    Williams, Jonathan
    Max Planck Institute for Chemistry, Mainz, Germany.
    Andreae, Meinrat
    Max Planck Institute for Chemistry, Mainz, Germany.
    Do organics contribute to small particle formation in the Amazonian upper troposphere?2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, no L17810, p. 5-Article in journal (Refereed)
    Abstract [en]

    3-D cloud-resolving model simulations including explicit aerosol physics and chemistry are compared with observations of upper tropospheric (12 km) aerosol size distributions over the Amazon Basin. The model underestimates the aerosol number concentration for all modes, especially the nucleation mode (d < 18 nm). We show that a boundary layer SO2 mixing ratio of approximately 5 ppb would be needed in order to reproduce the high nucleation mode number concentrations observed. This high SO2 mixing ratio is very unlikely for the pristine Amazon Basin at this time of the year. Hence, it is suggested that vapours other than H2SO4 participate in the formation and growth of small aerosols. Using activation nucleation theory together with a small (0.4–10%) secondary organic aerosol mass yield, we show that isoprene has the potential of substantially increasing the number of small particles formed as well as reducing the underestimate for the larger aerosol modes.

  • 28.
    Engström, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Bender, Frida A.-M.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Charlson, R. J.
    Wood, R.
    The nonlinear relationship between albedo and cloud fraction on near-global, monthly mean scale in observations and in the CMIP5 model ensemble2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 21, p. 9571-9578Article in journal (Refereed)
    Abstract [en]

    We study the relation between monthly mean albedo and cloud fraction over ocean,60∘S–60∘N. Satellite obser vations indicate that these clouds all fall on the same near-exponential curve,with a monotonic distribution over the ranges of cloud fractions and albedo. Using these observational dataas a reference, we examine the degree to which 26 climate models capture this feature of the near-globalmarine cloud population. Models show a general increase in albedo with increasing cloud fraction, but noneof them display a relation that is as well defined as that characterizing the observations. Models t ypicallydisplay larger albedo variability at a given cloud fraction, larger sensitivity in albedo to changes in cloudfraction, and lower cloud fractions. Several models also show branched distributions, contrasting with thesmooth observational relation. In the models the present-day cloud scenes are more reflective than thepreindustrial, demonstrating the simulated impact of anthropogenic aerosols on planetary albedo.

  • 29.
    Engström, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M.L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Impact of meteorological factors on the correlation between aerosol optical depth and cloud fraction2010In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, p. L18814-Article in journal (Refereed)
    Abstract [en]

    The aerosol optical depth has in several recent studies been found to correlate with cloud fraction. This study examines the global distribution of the total correlation between aerosol optical depth, cloud fraction and meteorological conditions using satellite observations together with atmospheric re-analysis data from the ECMWF. The results show large regional differences in the correlation between aerosol optical depth and cloud fraction, where a higher correlation is found over remote ocean. The one meteorological variable that correlates significantly with both aerosol optical depth and cloud fraction is the 10-meter wind speed. Constructing the partial correlation between aerosol optical depth and cloud fraction, with the impact from 10-meter wind speed removed, yields a significant difference compared to the total correlation. In several regions the remaining partial correlation is reduced from 0.4 to below 0.1. The results highlight the need to investigate all possible correlations between meteorological variables, cloud properties and aerosols. Citation: Engstrom, A., and A. M. L. Ekman (2010), Impact of meteorological factors on the correlation between aerosol optical depth and cloud fraction

  • 30.
    Engström, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M.L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    de Reus, Marian
    Wang, Chien
    Observational and modelling evidence of tropical deep convective clouds as a source of mid-tropospheric accumulation mode aerosols2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, p. L23813-Article in journal (Refereed)
    Abstract [en]

    High concentrations (up to 550 cm−3 STP) of aerosols in the accumulation mode (>0.12 μm) were observed by aircraft above 7.5 km altitude in the dynamically active regions of several deep convective clouds during the INDOEX campaign. Using a coupled 3-D aerosol-cloud-resolving model, we find that significant evaporation of hydrometeors due to strong updrafts and exchange with ambient air occurs at the boundaries and within the cloud tower. Assuming that each evaporated hydrometeor release an aerosol, an increase in the aerosol concentration by up to 600 cm−3 STP is found in the model at altitudes between 6 and 10 km. The evaporation and release of aerosols occur as the cloud develops, suggesting that deep convective clouds are important sources of mid-tropospheric aerosols during their active lifetime. This source may significantly impact the vertical distribution as well as long-range transport of aerosols in the free troposphere.

  • 31. Facchini, Maria Cristina
    et al.
    Rinaldi, Matteo
    Decesari, Stefano
    Carbone, Claudio
    Finessi, Emanuela
    Mircea, Mihaela
    Fuzzi, Sandro
    Ceburnis, Darius
    Flanagan, Robert
    Nilsson, E. Douglas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    de Leeuw, Gerrit
    Martino, Manuela
    Woeltjen, Janina
    O'Dowd, Colin D.
    Primary submicron marine aerosol dominated by insoluble organic colloids and aggregates2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, no 17, p. L17814-Article in journal (Refereed)
    Abstract [en]

    The chemical properties of sea-spray aerosol particles produced by artificially generated bubbles using oceanic waters were investigated during a phytoplankton bloom in the North Atlantic. Spray particles exhibited a progressive increase in the organic matter ( OM) content from 3 +/- 0.4% up to 77 +/- 5% with decreasing particle diameter from 8 to 0.125 mu m. Submicron OM was almost entirely water insoluble (WIOM) and consisted of colloids and aggregates exuded by phytoplankton. Our observations indicate that size dependent transfer of sea water organic material to primary marine particles is mainly controlled by the solubility and surface tension properties of marine OM. The pattern of WIOM and sea-salt content in the different size intervals observed in bubble bursting experiments is similar to that measured in atmospheric marine aerosol samples collected during periods of high biological activity. The results point to a WIOM/sea-salt fingerprint associated with submicron primary marine aerosol production in biologically rich waters.

  • 32.
    Finke, Kathrin
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hannachi, Abdel
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tropospheric Response to Stratospheric Variability via Lagged Quantile Regression2022In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 49, no 15, article id e2022GL099231Article in journal (Refereed)
    Abstract [en]

    Stratospheric variability may affect tropospheric weather on time scales between a few weeks and a few months, thus providing great potential for sub-seasonal to seasonal weather forecasts of extremes. Unlike standard linear regression, which is based on the conditional mean of the response variable, lagged quantile regression is used here, which enables modeling the response variable's complete conditional distribution. Using the ERA5 reanalysis, we explore the relation of prominent teleconnection indices and gridded tropospheric fields to the stratosphere during boreal winter for various quantiles and lags. Significant differences in duration, strength, and direction of the stratosphere-troposphere connection in outer quantiles compared to the median are identified. In particular, tropospheric extremes and their relation to the polar vortex strength are discussed, and an outlook is given.

  • 33. Fredriksen, Hege-Beate
    et al.
    Smith, Christopher J.
    Modak, Angshuman
    Stockholm University, Faculty of Science, Department of Meteorology . Indian Institute of Technology Bombay, India.
    Rugenstein, Maria
    21st Century Scenario Forcing Increases More for CMIP6 Than CMIP5 Models2023In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 50, no 6, article id e2023GL102916Article in journal (Refereed)
    Abstract [en]

    Although the Coupled Model Intercomparison Project 6 (CMIP6) protocol provides an experiment to estimate effective radiative forcing (ERF), it is only quantified for few models. We present new estimates of ERF for models participating in CMIP6 by applying the method developed in Fredriksen et al. (2021, https://doi.org/10.1029/2020JD034145), and validate our approach with available fixed-SST forcing estimates. We estimate ERF for experiments with abrupt changes of CO2, 1% increase of CO2, historical forcings, and future scenarios, and demonstrate that CMIP6 ERF is lower than CMIP5 ERF at the end of the historical period, but grows faster than CMIP5 in the future scenarios, ending up at higher levels than CMIP5 at the end of the 21st century. The simulated radiative efficiency of CO2 has not changed much, suggesting that the larger future increase in CO2 concentrations in CMIP6 compared to CMIP5 is important for explaining the forcing difference.

  • 34. Frob, F.
    et al.
    Olsen, A.
    Becker, M.
    Chafik, Léon
    Stockholm University, Faculty of Science, Department of Meteorology . University of Bergen, Norway.
    Johannessen, T.
    Reverdin, G.
    Omar, A.
    Wintertime fCO(2) Variability in the Subpolar North Atlantic Since 20042019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 3, p. 1580-1590Article in journal (Refereed)
    Abstract [en]

    Winter data of surface ocean temperature (SST), salinity (SSS) and CO2 fugacity (fCO(2)) collected on the VOS M/V Nuka Arctica in the subpolar North Atlantic between 2004 and 2017 are used to establish trends, drivers, and interannual variability. Over the period, waters cooled and freshened, and the fCO(2) increased at a rate similar to the atmospheric CO2 growth rate. When accounting for the freshening, the inferred increase in dissolved inorganic carbon (DIC) was found to be approximately twice that expected from atmospheric CO2 alone. This is attributed to the cooling. In the Irminger Sea, fCO(2) exhibited additional interannual variations driven by atmospheric forcing through winter mixing. As winter fCO(2) in the region is close to the atmospheric, the subpolar North Atlantic has varied between being slightly supersaturated and slightly undersaturated over the investigated period. Plain Language Summary The global oceans take up roughly a quarter of carbon dioxide (CO2) from fossil fuels and industry per year. As the emissions of CO2 increase, the amount of CO2 taken up by the oceans should increase in proportion; however, the ability of the ocean to remove CO2 from the atmosphere varies on interannual to decadal time scales. Here we assess processes that drive short-term variability and long-term trends of the subpolar North Atlantic carbon sink based on observational data obtained during winters between 2004 and 2017. We find that the subpolar North Atlantic has indeed kept pace with rising emissions over the entire period of time, which was mainly attributed to solubility-driven uptake of CO2. Year-to-year changes of the surface ocean partial pressure of CO2 can be linked to the depth of the winter mixed layer as well as atmospheric forcing. In general, the North Atlantic has shifted between a small source and a small sink of atmospheric CO2 during wintertime. Our results underline the need to maintain long-term physical, chemical, and biological observations in order monitor the ocean CO2 sink and understand the processes driving variability.

  • 35. Gagen, Mary
    et al.
    Zorita, Eduardo
    McCarroll, Danny
    Young, Giles H. F.
    Grudd, Håkan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jalkanen, Risto
    Loader, Neil J.
    Robertson, Iain
    Kirchhefer, Andreas
    Cloud response to summer temperatures in Fennoscandia over the last thousand years2011In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, p. L05701-Article in journal (Refereed)
    Abstract [en]

    Cloud cover is one of the most important factors controlling the radiation balance of the Earth. The response of cloud cover to increasing global temperatures represents the largest uncertainty in model estimates of future climate because the cloud response to temperature is not well-constrained. Here we present the first regional reconstruction of summer sunshine over the past millennium, based on the stable carbon isotope ratios of pine treerings from Fennoscandia. Comparison with the regional temperature evolution reveals the Little Ice Age (LIA) to have been sunny, with cloudy conditions in the warmest periods of the Medieval at this site. A negative shortwave cloud feedback is indicated at high latitude. A millennial climate simulation suggests that regionally low temperatures during the LIA were mostly maintained by a weaker greenhouse effect due to lower humidity. Simulations of future climate that display a negative shortwave cloud feedback for high-latitudes are consistent with our proxy interpretation. Citation: Gagen, M., E. Zorita, D. McCarroll, G. H. F. Young, H. Grudd, R. Jalkanen, N. J. Loader, I. Robertson, and A. Kirchhefer (2011), Cloud response to summer temperatures in Fennoscandia over the last thousand years, Geophys. Res. Lett., 38, L05701, doi:10.1029/2010GL046216.

  • 36. Goodrich, Jordan P.
    et al.
    Varner, Ruth K.
    Frolking, Steve
    Duncan, Bryan N.
    Crill, Patrick M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    High-frequency measurements of methane ebullition over a growing season at a temperate peatland site2011In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, p. L07404-Article in journal (Refereed)
    Abstract [en]

    Bubbles can contribute a significant fraction of methane emissions from wetlands; however the range of reported fractions is very large and accurate characterization of this pathway has proven difficult. Here we show that continuous automated flux chambers combined with an integrated cavity output spectroscopy (ICOS) instrument allow us to quantify both CH(4) ebullition rate and magnitude. For a temperate poor fen in 2009, ebullition rate varied on hourly to seasonal time scales. A diel pattern in ebullition was identified with peak release occurring between 20:00 and 06:00 local time, though steady fluxes (i.e., those with a linear increase in chamber headspace CH(4) concentration) did not exhibit diel variability. Seasonal mean ebullition rates peaked at 843.5 +/- 384.2 events m(-2) d(-1) during the summer, with a mean magnitude of 0.19 mg CH(4) released in each event.

  • 37.
    Gumbel, Jörg
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Fan, Z. Y.
    Waldemarsson, T.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Stegman, Jacek
    Stockholm University, Faculty of Science, Department of Meteorology .
    Witt, Georg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Llewellyn, E. J.
    She, C. -Y
    Plane, J. M. C.
    Retrieval of global mesospheric sodium densities from the Odin satellite2007In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 34, no 4, p. L04813-Article in journal (Refereed)
    Abstract [en]

    Satellite observations of the Na D dayglow at 589 nm provide a global database for the climatology of the mesospheric sodium layer. More than five years of Na D limb observations are available from the Optical Spectrograph and InfraRed Imager System onboard the Odin satellite. We describe a robust retrieval method that provides individual sodium density profiles with a typical accuracy of 20% and altitude resolution of 2 km. Retrieved column abundances and density profiles are validated against sodium resonance lidar measurements at mid- latitudes. Examples of the seasonal and latitudinal variation of the sodium layer illustrate Odin's potential for climatological studies of mesospheric metals.

  • 38.
    Han, Zixuan
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI). Hohai University, China; Chinese Academy of Sciences (CAS), China.
    Power, Katherine
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Li, Gen
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Impacts of Mid-Pliocene Ice Sheets and Vegetation on Afro-Asian Summer Monsoon Rainfall Revealed by EC-Earth Simulations2024In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 51, no 2, article id e2023GL106145Article in journal (Refereed)
    Abstract [en]

    The impact of mid-Pliocene boundary conditions on Afro-Asian summer monsoon (AfroASM) rainfall is examined using the fully coupled Earth System Model EC-Earth3-LR. Our focus lies on the effects of varying CO2 concentration, diminished ice sheets and vegetation dynamics. We find that the enhanced AfroASM rainfall is predominantly caused by the “warmer-gets-wetter” mechanism due to elevated CO2 levels. Additionally, the ice sheet, similar in size to that of the mid-Pliocene era, creates several indirect effects. These include sea ice-albedo feedback and inter-hemispheric atmosphere energy transport. Such influences result in the southward shift of Hadley circulation and formation of Pacific-Japan pattern, leading to reduced rainfall in North African and South Asian monsoon regions but increased rainfall in East Asian monsoon region. Interestingly, while dynamic vegetation feedback has a minimal direct effect on AfroASM rainfall, it significantly influences rainfall in the mid-high latitudes of the North Hemisphere by enhancing water vapor feedback.

  • 39.
    Hanley, John
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    The role of large-scale atmospheric flow and Rossby wave breaking in the evolution of extreme windstorms over Europe2012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, p. L21708-Article in journal (Refereed)
    Abstract [en]

    We investigate the relationship between large-scale atmospheric flow and the evolution of the most extreme windstorms affecting Western Continental Europe. The 25 most destructive Western Continental European wind storms are selected from a 43-year climatology. 22 of these storms are grouped as having a similar trajectory and evolution. We show that these storms typically occur during particularly strong and persistent positive NAO anomalies which peak approximately 2 days before the storms' peak intensity; the NAO pattern then shifts eastward to a position over the European continent when the storms strike Europe. A temporal composite of potential temperature on the 2-PVU surface suggests that this NAO shift is the result of simultaneous cyclonic and anticyclonic wave breaking penetrating further to the east than during a typical high-NAO event. This creates an extremely intense, zonally-orientated jet over the North Atlantic whose baroclinicity favours explosive intensification of storms while steering them into Western Continental Europe.

  • 40.
    Hannachi, Abdelwaheb
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Turner, A. G.
    Isomap nonlinear dimensionality reduction and bimodality of Asian monsoon convection2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 8, p. 1653-1658Article in journal (Refereed)
    Abstract [en]

    It is known that the empirical orthogonal function method is unable to detect possible nonlinear structure in climate data. Here, isometric feature mapping (Isomap), as a tool for nonlinear dimensionality reduction, is applied to 19582001 ERA-40 sea-level pressure anomalies to study nonlinearity of the Asian summer monsoon intraseasonal variability. Using the leading two Isomap time series, the probability density function is shown to be bimodal. A two-dimensional bivariate Gaussian mixture model is then applied to identify the monsoon phases, the obtained regimes representing enhanced and suppressed phases, respectively. The relationship with the large-scale seasonal mean monsoon indicates that the frequency of monsoon regime occurrence is significantly perturbed in agreement with conceptual ideas, with preference for enhanced convection on intraseasonal time scales during large-scale strong monsoons. Trend analysis suggests a shift in concentration of monsoon convection, with less emphasis on South Asia and more on the East China Sea.

  • 41. Harden, Jennifer W.
    et al.
    Koven, Charles D.
    Ping, Chien-Lu
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    McGuire, A. David
    Camill, Phillip
    Jorgenson, Torre
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Michaelson, Gary J.
    O'Donnell, Jonathan A.
    Schuur, Edward A. G.
    Tarnocai, Charles
    Johnson, Kristopher
    Grosse, Guido
    Field information links permafrost carbon to physical vulnerabilities of thawing2012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, p. L15704-Article in journal (Refereed)
    Abstract [en]

    Deep soil profiles containing permafrost (Gelisols) were characterized for organic carbon (C) and total nitrogen (N) stocks to 3 m depths. Using the Community Climate System Model (CCSM4) we calculate cumulative distributions of active layer thickness (ALT) under current and future climates. The difference in cumulative ALT distributions over time was multiplied by C and N contents of soil horizons in Gelisol suborders to calculate newly thawed C and N. Thawing ranged from 147 PgC with 10 PgN by 2050 (representative concentration pathway RCP scenario 4.5) to 436 PgC with 29 PgN by 2100 (RCP 8.5). Organic horizons that thaw are vulnerable to combustion, and all horizon types are vulnerable to shifts in hydrology and decomposition. The rates and extent of such losses are unknown and can be further constrained by linking field and modelling approaches. These changes have the potential for strong additional loading to our atmosphere, water resources, and ecosystems. Citation: Harden, J. W., et al. (2012), Field information links permafrost carbon to physical vulnerabilities of thawing, Geophys. Res. Lett., 39, L15704, doi: 10.1029/2012GL051958.

  • 42.
    Harnik, Nili
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Tel Aviv University, Israel.
    Messori, Gabriele
    Stockholm University, Faculty of Science, Department of Meteorology .
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    Feldstein, Steven B.
    The Circumglobal North American wave pattern and its relation to cold events in eastern North America2016In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 43, no 20, p. 11015-11023Article in journal (Refereed)
    Abstract [en]

    Extreme large-scale North American cold events are associated with strong undulations in the tropospheric jet stream which bring cold polar air southward over the continent. Here we propose that these jet undulations are associated with the North American part of the Circumglobal Teleconnection Patterna pair of zonally oriented waves of zonal wave number 5 which are in zonal quadrature with each other. While the Pacific/North American pattern is associated with the first circumglobal wave pattern, North American extreme cold events are associated with the second pattern. The 300hPa meridional wind and surface temperature anomalies associated with the Circumglobal North American wave packet are similar to those associated with the strongest eastern U.S. cold events. Both types of events are associated with a wave packet propagating all the way from Asia across the Pacific and across North America, with cold temperature anomalies spreading southeastward from Canada over the continent.

  • 43. Hartl-Meier, C. T. M.
    et al.
    Büntgen, U.
    Smerdon, J. E.
    Zorita, E.
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of Cambridge, UK; Navarino Environmental Observatory, Greece.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Schneider, L.
    Esper, J.
    Temperature Covariance in Tree Ring Reconstructions and Model Simulations Over the Past Millennium2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 18, p. 9458-9469Article in journal (Refereed)
    Abstract [en]

    Spatial covariance in the simulated temperature evolution over the past millennium has been reported to exceed that of multiproxy-based reconstructions. Here we use tree ring-based temperature reconstructions and state-of-the-art climate model simulations to assess temporal changes in Northern Hemisphere intercontinental temperature covariance during the last 1000 years. Tree ring-only approaches reveal stronger agreement with model simulations compared to multiproxy networks. Although simulated temperatures exhibit a substantial spread among individual models, intercontinental temperature coherency is mainly driven by the cooling of large volcanic eruptions in 1257, 1452, 1600, and 1815 Common Era. The coherence of these synchronizing events appears to be elevated in several climate simulations relative to their own unforced covariance baselines and in comparison to the proxy reconstructions. This suggests that some models likely overestimate the amplitude of abrupt summer cooling in response to volcanic eruptions, particularly at larger spatial scales.

  • 44.
    Hendrickx, Koen
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Megner, Linda
    Stockholm University, Faculty of Science, Department of Meteorology .
    Marsh, Daniel R.
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Strandberg, Rickard
    Stockholm University, Faculty of Science, Department of Mathematics.
    Martinsson, Felix
    Stockholm University, Faculty of Science, Department of Mathematics.
    Relative Importance of Nitric Oxide Physical Drivers in the Lower Thermosphere2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 19, p. 10081-10087Article in journal (Refereed)
    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.

  • 45. Hennigan, Christopher J.
    et al.
    Westervelt, Daniel M.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Engelhart, Gabriella J.
    Lee, Taehyoung
    Collett, Jeffrey L., Jr.
    Pandis, Spyros N.
    Adams, Peter J.
    Robinson, Allen L.
    New particle formation and growth in biomass burning plumes: An important source of cloud condensation nuclei2012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, p. L09805-Article in journal (Refereed)
    Abstract [en]

    Experiments were performed in an environmental chamber to characterize the effects of photo-chemical aging on biomass burning emissions. Photo-oxidation of dilute exhaust from combustion of 12 different North American fuels induced significant new particle formation that increased the particle number concentration by a factor of four (median value). The production of secondary organic aerosol caused these new particles to grow rapidly, significantly enhancing cloud condensation nuclei (CCN) concentrations. Using inputs derived from these new data, global model simulations predict that nucleation in photo-chemically aging fire plumes produces dramatically higher CCN concentrations over widespread areas of the southern hemisphere during the dry, burning season (Sept.-Oct.), improving model predictions of surface CCN concentrations. The annual indirect forcing from CCN resulting from nucleation and growth in biomass burning plumes is predicted to be -0.2 W m(-2), demonstrating that this effect has a significant impact on climate that has not been previously considered. Citation: Hennigan, C. J., D. M. Westervelt, I. Riipinen, G. J. Engelhart, T. Lee, J. L. Collett Jr., S. N. Pandis, P. J. Adams, and A. L. Robinson (2012), New particle formation and growth in biomass burning plumes: An important source of cloud condensation nuclei, Geophys. Res. Lett., 39, L09805, doi: 10.1029/2012GL050930.

  • 46. Hochman, Assaf
    et al.
    Messori, Gabriele
    Stockholm University, Faculty of Science, Department of Meteorology . Uppsala University, Sweden.
    Quinting, Julian F.
    Pinto, Joaquim G.
    Grams, Christian M.
    Do Atlantic-European Weather Regimes Physically Exist?2021In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 20, article id e2021GL095574Article in journal (Refereed)
    Abstract [en]

    The subseasonal variability of the extratropical large-scale atmospheric flow is characterized by recurrent or quasi-stationary circulation anomalies, termed weather regimes. Despite the usefulness of these regimes in numerous meteorological and socioeconomic applications, there is an ongoing debate as to whether they represent physical modes of the atmosphere, or are merely useful statistical categorizations. Here, we answer this question for wintertime Atlantic-European regimes. We argue that dynamical systems theory applied to a refined regime definition provides strong evidence in support of most weather regimes being physically meaningful. This finding underpins the broad relevance of weather regimes, for understanding the response of the atmosphere to external forcing, supporting subseasonal weather forecasting, and down scaling of climate projections.

  • 47.
    Hock, Regine
    et al.
    University of Alaska Fairbanks.
    de Woul, Mattias
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Radic, Valentina
    University of British Columbia.
    Dyurgerov, Mark
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Mountain glaciers and ice caps around Antarctica make a large sea-level rise contribution2009In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36, no L07501Article in journal (Refereed)
    Abstract [en]

    The Intergovernmental Panel on Climate Change (IPCC) estimates that the sum of all contributions to sea‐level rise for the period 1961–2004 was 1.1 ± 0.5 mm a−1, leaving 0.7 ± 0.7 of the 1.8 ± 0.5 mm a−1 observed sea‐level rise unexplained. Here, we compute the global surface mass balance of all mountain glaciers and ice caps (MG&IC), and find that part of this much‐discussed gap can be attributed to a larger contribution than previously assumed from mass loss of MG&IC, especially those around the Antarctic Peninsula. We estimate global surface mass loss of all MG&IC as 0.79 ± 0.34 mm a−1 sea‐level equivalent (SLE) compared to IPCC's 0.50 ± 0.18 mm a−1. The Antarctic MG&IC contributed 28% of the global estimate due to exceptional warming around the Antarctic Peninsula and high sensitivities to temperature similar to those we find in Iceland, Patagonia and Alaska.

  • 48.
    Huusko, Linnea L.
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Modak, Angshuman
    Stockholm University, Faculty of Science, Department of Meteorology .
    Mauritsen, Thorsten
    Stockholm University, Faculty of Science, Department of Meteorology .
    Stronger Response to the Aerosol Indirect Effect Due To Cooling in Remote Regions2022In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 49, no 21, article id e2022GL101184Article in journal (Refereed)
    Abstract [en]

    It is often assumed that effective radiative forcings, regardless of forcing agent, are additive in the temperature change. Using climate model simulations with abruptly applied aerosol forcing we find that the temperature response per unit forcing is larger if induced by aerosol-cloud interactions than directly by aerosols. The spatial patterns of forcing and temperature change show that aerosol-cloud interactions induce cooling over remote oceans in the extratropics, whereas the effect of increased emissions is localized around the emission sources primarily over tropical land. The results are consistent with ideas of how the patterns of sea surface temperature impact radiative feedbacks, and a large forcing efficacy of aerosol-cloud interactions could help explain previously observed intermodel spread in the response to aerosols.

  • 49. Igel, Adele L.
    et al.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Savre, Julien
    Sedlar, Joseph
    Stockholm University, Faculty of Science, Department of Meteorology .
    The free troposphere as a potential source of arctic boundary layer aerosol particles2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 13, p. 7053-7060Article in journal (Refereed)
    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.

  • 50.
    Jakobsson, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mayer, Larry
    Coakley, Bernard
    Dowdeswell, Julian A.
    Forbes, Steve
    Fridman, Boris
    Hodnesdal, Hanne
    Noormets, Riko
    Pedersen, Richard
    Rebesco, Michele
    Schenke, Hans Werner
    Zarayskaya, Yulia
    Accettella, Daniela
    Armstrong, Andrew
    Anderson, Robert M.
    Bienhoff, Paul
    Camerlenghi, Angelo
    Church, Ian
    Edwards, Margo
    Gardner, James V.
    Hall, John K.
    Hell, Benjamin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hestvik, Ole
    Kristoffersen, Yngve
    Marcussen, Christian
    Mohammad, Rezwan
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Mosher, David
    Nghiem, Son V.
    Teresa Pedrosa, Maria
    Travaglini, Paola G.
    Weatherall, Pauline
    The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.02012In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 39, article id L12609Article in journal (Refereed)
    Abstract [en]

    The International Bathymetric Chart of the Arctic Ocean (IBCAO) released its first gridded bathymetric compilation in 1999. The IBCAO bathymetric portrayals have since supported a wide range of Arctic science activities, for example, by providing constraint for ocean circulation models and the means to define and formulate hypotheses about the geologic origin of Arctic undersea features. IBCAO Version 3.0 represents the largest improvement since 1999 taking advantage of new data sets collected by the circum-Arctic nations, opportunistic data collected from fishing vessels, data acquired from US Navy submarines and from research ships of various nations. Built using an improved gridding algorithm, this new grid is on a 500 meter spacing, revealing much greater details of the Arctic seafloor than IBCAO Version 1.0 (2.5 km) and Version 2.0 (2.0 km). The area covered by multibeam surveys has increased from similar to 6% in Version 2.0 to similar to 11% in Version 3.0. Citation: Jakobsson, M., et al. (2012), The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.0, Geophys. Res. Lett., 39, L12609, doi:10.1029/2012GL052219.

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