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  • 1.
    Bulatovic, Ines
    et al.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Igel, Adele L.
    Leck, Caroline
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Heintzenberg, Jost
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Riipinen, Ilona
    Stockholms universitet, Institutionen för miljövetenskap.
    Ekman, Annica M. L.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    The importance of Aitken mode aerosol particles for cloud sustenance in the summertime high Arctic: A simulation study supported by observational data2021Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 21, nr 5, s. 3871-3897Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The potential importance of Aitken mode particles (diameters similar to 25-80 nm) for stratiform mixed-phase clouds in the summertime high Arctic (> 80 degrees N) has been investigated using two large-eddy simulation models. We find that, in both models, Aitken mode particles significantly affect the simulated microphysical and radiative properties of the cloud and can help sustain the cloud when accumulation mode concentrations are low (< 10-20 cm-3), even when the particles have low hygroscopicity (hygroscopicity parameter - kappa = 0.1). However, the influence of the Aitken mode decreases if the overall liquid water content of the cloud is low, either due to a higher ice fraction or due to low radiative cooling rates. An analysis of the simulated supersaturation (ss) statistics shows that the ss frequently reaches 0.5 % and sometimes even exceeds 1 %, which confirms that Aitken mode particles can be activated. The modelling results are in qualitative agreement with observations of the Hoppel minimum obtained from four different expeditions in the high Arctic. Our findings highlight the importance of better understanding Aitken mode particle formation, chemical properties and emissions, particularly in clean environments such as the high Arctic.

  • 2. Igel, Adele L.
    et al.
    Ekman, Annica M. L.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Leck, Caroline
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Tjernström, Michael
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Savre, Julien
    Sedlar, Joseph
    Stockholms universitet, Meteorologiska institutionen (MISU).
    The free troposphere as a potential source of arctic boundary layer aerosol particles2017Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, nr 13, s. 7053-7060Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 3.
    Siegel, Karolina
    et al.
    Stockholms universitet, Institutionen för miljövetenskap.
    Neuberger, Almuth
    Stockholms universitet, Institutionen för miljövetenskap.
    Karlsson, Linn
    Stockholms universitet, Institutionen för miljövetenskap.
    Zieger, Paul
    Stockholms universitet, Institutionen för miljövetenskap.
    Mattsson, Fredrik
    Stockholms universitet, Institutionen för miljövetenskap.
    Duplessis, Patrick
    Dada, Lubna
    Daellenbach, Kaspar
    Schmale, Julia
    Baccarini, Andrea
    Krejci, Radovan
    Stockholms universitet, Institutionen för miljövetenskap.
    Svenningsson, Birgitta
    Chang, Rachel
    Ekman, Annica M. L.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Riipinen, Ilona
    Stockholms universitet, Institutionen för miljövetenskap.
    Mohr, Claudia
    Stockholms universitet, Institutionen för miljövetenskap.
    Using Novel Molecular-Level Chemical Composition Observations of High Arctic Organic Aerosol for Predictions of Cloud Condensation Nuclei2022Inngår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 56, nr 19, s. 13888-13899Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Predictions of cloud droplet activation in the late summertime (September) central Arctic Ocean are made using κ-Köhler theory with novel observations of the aerosol chemical composition from a high-resolution time-of-flight chemical ionization mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS) and an aerosol mass spectrometer (AMS), deployed during the Arctic Ocean 2018 expedition onboard the Swedish icebreaker Oden. We find that the hygroscopicity parameter κ of the total aerosol is 0.39 ± 0.19 (mean ± std). The predicted activation diameter of ∼25 to 130 nm particles is overestimated by 5%, leading to an underestimation of the cloud condensation nuclei (CCN) number concentration by 4-8%. From this, we conclude that the aerosol in the High Arctic late summer is acidic and therefore highly cloud active, with a substantial CCN contribution from Aitken mode particles. Variability in the predicted activation diameter is addressed mainly as a result of uncertainties in the aerosol size distribution measurements. The organic κ was on average 0.13, close to the commonly assumed κ of 0.1, and therefore did not significantly influence the predictions. These conclusions are supported by laboratory experiments of the activation potential of seven organic compounds selected as representative of the measured aerosol.

  • 4.
    Sotiropoulou, Georgia
    et al.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Ickes, Luisa
    Nenes, Athanasios
    Ekman, Annica M. L.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Ice multiplication from ice-ice collisions in the high Arctic: sensitivity to ice habit, rimed fraction, ice type and uncertainties in the numerical description of the process2021Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 21, nr 12, s. 9741-9760Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Atmospheric models often fail to correctly reproduce the microphysical structure of Arctic mixed-phase clouds and underpredict ice water content even when the simulations are constrained by observed levels of ice nucleating particles. In this study we investigate whether ice multiplication from breakup upon ice-ice collisions, a process missing in most models, can account for the observed cloud ice in a stratocumulus cloud observed during the Arctic Summer Cloud Ocean Study (ASCOS) campaign. Our results indicate that the efficiency of this process in these conditions is weak; increases in fragment generation are compensated for by subsequent enhancement of precipitation and subcloud sublimation. Activation of collisional breakup improves the representation of cloud ice content, but cloud liquid remains overestimated. In most sensitivity simulations, variations in ice habit and prescribed rimed fraction have little effect on the results. A few simulations result in explosive multiplication and cloud dissipation; however, in most setups, the overall multiplication effects become substantially weaker if the precipitation sink is enhanced through cloud-ice-to-snow autoconversion. The largest uncertainty stems from the correction factor for ice enhancement due to sublimation included in the breakup parameterization; excluding this correction results in rapid glaciation, especially in simulations with plates. Our results indicate that the lack of a detailed treatment of ice habit and rimed fraction in most bulk microphysics schemes is not detrimental for the description of the collisional breakup process in the examined conditions as long as cloud-ice-to-snow autoconversion is considered.

  • 5. Stevens, Robin G.
    et al.
    Loewe, Katharina
    Dearden, Christopher
    Dimitrelos, Antonios
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Possner, Anna
    Eirund, Gesa K.
    Raatikainen, Tomi
    Hill, Adrian A.
    Shipway, Benjamin J.
    Wilkinson, Jonathan
    Romakkaniemi, Sami
    Tonttila, Juha
    Laaksonen, Ari
    Korhonen, Hannele
    Connolly, Paul
    Lohmann, Ulrike
    Hoose, Corinna
    Ekman, Annica M. L.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Carslaw, Ken S.
    Field, Paul R.
    A model intercomparison of CCN-limited tenuous clouds in the high Arctic2018Inngår i: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 18, nr 15, s. 11041-11071Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We perform a model intercomparison of summertime high Arctic ( > 80 degrees N) clouds observed during the 2008 Arctic Summer Cloud Ocean Study (ASCOS) campaign, when observed cloud condensation nuclei (CCN) concentrations fell below 1 cm(-3). Previous analyses have suggested that at these low CCN concentrations the liquid water content (LWC) and radiative properties of the clouds are determined primarily by the CCN concentrations, conditions that have previously been referred to as the tenuous cloud regime. The intercomparison includes results from three large eddy simulation models (UCLALES-SALSA, COSMO-LES, and MIMICA) and three numerical weather prediction models (COSMO-NWP, WRF, and UM-CASIM). We test the sensitivities of the model results to different treatments of cloud droplet activation, including prescribed cloud droplet number concentrations (CDNCs) and diagnostic CCN activation based on either fixed aerosol concentrations or prognostic aerosol with in-cloud processing. There remains considerable diversity even in experiments with prescribed CDNCs and prescribed ice crystal number concentrations (ICNC). The sensitivity of mixed-phase Arctic cloud properties to changes in CDNC depends on the representation of the cloud droplet size distribution within each model, which impacts autoconversion rates. Our results therefore suggest that properly estimating aerosol-cloud interactions requires an appropriate treatment of the cloud droplet size distribution within models, as well as in situ observations of hydrometeor size distributions to constrain them. The results strongly support the hypothesis that the liquid water content of these clouds is CCN limited. For the observed meteorological conditions, the cloud generally did not collapse when the CCN concentration was held constant at the relatively high CCN concentrations measured during the cloudy period, but the cloud thins or collapses as the CCN concentration is reduced. The CCN concentration at which collapse occurs varies substantially between models. Only one model predicts complete dissipation of the cloud due to glaciation, and this occurs only for the largest prescribed ICNC tested in this study. Global and regional models with either prescribed CDNCs or prescribed aerosol concentrations would not reproduce these dissipation events. Additionally, future increases in Arctic aerosol concentrations would be expected to decrease the frequency of occurrence of such cloud dissipation events, with implications for the radiative balance at the surface. Our results also show that cooling of the sea-ice surface following cloud dissipation increases atmospheric stability near the surface, further suppressing cloud formation. Therefore, this suggests that linkages between aerosol and clouds, as well as linkages between clouds, surface temperatures, and atmospheric stability need to be considered for weather and climate predictions in this region.

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