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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 11 | Copyright
Atmos. Chem. Phys., 17, 6693-6704, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Jun 2017

Research article | 08 Jun 2017

Modelling micro- and macrophysical contributors to the dissipation of an Arctic mixed-phase cloud during the Arctic Summer Cloud Ocean Study (ASCOS)

Katharina Loewe1, Annica M. L. Ekman2, Marco Paukert1,a, Joseph Sedlar3, Michael Tjernström2, and Corinna Hoose1 Katharina Loewe et al.
  • 1Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karslruhe, Germany
  • 2Department of Meteorology and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 3Swedish Meteorological Hydrological Institute, Norrköping, Sweden
  • anow at: Pacific Northwest National Laboratory, Richland, Washington, USA

Abstract. The Arctic climate is changing; temperature changes in the Arctic are greater than at midlatitudes, and changing atmospheric conditions influence Arctic mixed-phase clouds, which are important for the Arctic surface energy budget. These low-level clouds are frequently observed across the Arctic. They impact the turbulent and radiative heating of the open water, snow, and sea-ice-covered surfaces and influence the boundary layer structure. Therefore the processes that affect mixed-phase cloud life cycles are extremely important, yet relatively poorly understood. In this study, we present sensitivity studies using semi-idealized large eddy simulations (LESs) to identify processes contributing to the dissipation of Arctic mixed-phase clouds. We found that one potential main contributor to the dissipation of an observed Arctic mixed-phase cloud, during the Arctic Summer Cloud Ocean Study (ASCOS) field campaign, was a low cloud droplet number concentration (CDNC) of about 2cm−3. Introducing a high ice crystal concentration of 10L−1 also resulted in cloud dissipation, but such high ice crystal concentrations were deemed unlikely for the present case. Sensitivity studies simulating the advection of dry air above the boundary layer inversion, as well as a modest increase in ice crystal concentration of 1L−1, did not lead to cloud dissipation. As a requirement for small droplet numbers, pristine aerosol conditions in the Arctic environment are therefore considered an important factor determining the lifetime of Arctic mixed-phase clouds.

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Processes that affect Arctic mixed-phase cloud life cycle are extremely important for the surface energy budget. Three different sensitivity experiments mimic changes in the advection of air masses with different thermodynamic profiles and aerosol properties to find the potential mechanisms leading to the dissipation of the cloud. We found that the reduction of the cloud droplet number concentration was likely the primary contributor to the dissipation of the observed Arctic mixed-phase cloud.
Processes that affect Arctic mixed-phase cloud life cycle are extremely important for the...