14 Apr 2022
14 Apr 2022
Status: this preprint is currently under review for the journal ACP.

Aerosol-stratocumulus interactions: Towards a better process understanding using closures between observations and large eddy simulations

Silvia Margarita Calderón1, Juha Tonttila1, Angela Buchholz2, Jorma Joutsensaari2, Mika Komppula1, Ari Leskinen1,2, Liqing Hao2, Dmitri Moisseev3,4, Iida Pullinen2, Petri Tiitta1, Jian Xu5, Annele Virtanen2, Harri Kokkola1, and Sami Romakkaniemi1 Silvia Margarita Calderón et al.
  • 1Atmospheric Research Centre of Eastern Finland, Finnish Meteorological Institute, P.O. Box 1627, 70211 Kuopio, Finland
  • 2Department of Applied Physics, University of Eastern Finland
  • 3Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland
  • 4Finnish Meteorological Institute, Helsinki, Finland
  • 5Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungzentrum Jülich GmbH, 52425 Jülich, Germany

Abstract. We studied two cases of cloud formation, one diurnal (24 September 2020) and one nocturnal (31 October 2020), with high and low aerosol loadings, respectively. Aerosol number concentrations differ more than 1 order of magnitude between cases and therefore, lead to cloud droplet number concentration (CDNC) values which range from less than 100 cm-3 up to 1000 cm-3. Different aerosol loadings affected supersaturations at the cloud base, and thus the size of aerosol particles activating to cloud droplets. Due to higher CDNC, the mean size of cloud droplets in the diurnal-high aerosol case was lower. Thus, droplet evaporation in downdrafts affected more the observed CDNC at Puijo altitude compared to the low aerosol case. In addition, in the low aerosol case, the presence of large aerosol particles in the accumulation mode played a significant role in the droplet spectrum evolution as it promoted the drizzle formation through collision and coalescence processes. Also, during the event, the formation of ice particles was observed due to subzero temperature at the cloud top. Although the modeled number concentration of ice hydrometeors was too low to be directly measured, the retrieval of hydrometeor sedimentation velocities with cloud radar allowed us to assess the realism of modeled ice particles. The studied cases are presented in detail and can be further used by the cloud modellers to test and validate their models in a well-characterized modelling setup. We also provide recommendations on how increasing amount of information on aerosol properties could improve the understanding of processes affecting cloud droplet number and liquid water content in stratiform clouds.

Silvia Margarita Calderón et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Silvia Margarita Calderón et al.

Data sets

UCLALES-SALSA outputs for the manuscript "Aerosol-stratocumulus interactions: Towards better process understanding using closures between observations and large eddy simulations" Calderón, Silvia; Tonttila, Juha; Buchholz, Angela; Komppula, Mika; Leskinen, Ari; Liqing, Hao; Moisseev, Dmitri; Pullinen, Iida; Tiitta, Petri; Xu, Jian; Virtanen, Annele; Kokkola, Harri; Romakkaniemi, Sami ;

Model code and software

Large-eddy-simulations were performed with UCLALES-SALSA (DEV version 17.08.2021) Tonttila, Juha; Kokkola, Harri; Romakkaniemi, Sami ; Raatikainen, Tomi

Silvia Margarita Calderón et al.


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Short summary
The spatial and temporal restrictions of observations, and oversimplified aerosol representation in large-eddy-simulations (LES) limit our understanding of aerosol-stratocumulus interactions. In this closure study of in situ and remote sensing observations, and outputs from UCLALES-SALSA, we have assessed the role of convective overturning and aerosol effects in two cloud events observed at the Puijo SMEAR IV station, Finland, a diurnal-high aerosol case and a nocturnal-low aerosol case.