Low-level mixed-phase clouds in a complex Arctic environment

Atmospheric Chemistry and Physics

Marion Maturilli¹  Matthew D. Shupe²  Stefan Kneifel³  Kerstin Ebell³  Ulrich Löhnert³  Rosa Gierens³ 

[1]Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, Germany

[2]Cooperative Institute for the Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA

[3]Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA

[4]Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany

DOI  :  10.5194/acp-20-3459-2020

来源: publisher

【 摘 要 】

Low-level mixed-phase clouds (MPCs) are common in the Arctic. Both local and large-scale phenomena influence the properties and lifetime of MPCs. Arctic fjords are characterized by complex terrain and large variations in surface properties. Yet, not many studies have investigated the impact of local boundary layer dynamics and their relative importance on MPCs in the fjord environment. In this work, we used a combination of ground-based remote sensinginstruments, surface meteorological observations, radiosoundings, and reanalysis data to study persistent low-level MPCs at Ny-Ålesund, Svalbard, for a 2.5-year period. Methods to identify the cloud regime, surface coupling, and regional and local wind patterns were developed. We found that persistent low-level MPCs were most common with westerly winds, and the westerly clouds had a higher mean liquid (42 g m⁻²) and ice water path (16 g m⁻²) compared to those with easterly winds. The increased height and rarity of persistent MPCs with easterly free-tropospheric winds suggest the island and its orography have an influence on the studied clouds. Seasonal variation in the liquid water path was found to be minimal, although the occurrence of persistent MPCs, their height, and their ice water path all showed notable seasonal dependency. Most of the studied MPCs were decoupled from the surface (63 %–82 % of the time). The coupled clouds had 41 % higher liquid water path than the fully decoupled ones. Local winds in the fjord were related to the frequency of surface coupling, and we propose that katabatic winds from the glaciers in the vicinity of the station may cause clouds to decouple. We concluded that while the regional to large-scale wind direction was important for the persistent MPC occurrence and properties, the local-scale phenomena (local wind patterns in the fjord and surface coupling) also had an influence. Moreover, this suggests that local boundary layer processes should be described in models in order to present low-level MPC properties accurately.

【 授权许可】

Unknown