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

• Main Authors: Gierens, Rosa, Kneifel, Stefan, Shupe, Matthew D., Ebell, Kerstin, Maturilli, Marion, Löhnert, Ulrich
• Format: Text
• Language: English
• Published: 2019
• Subjects: Arctic; Ny-Ålesund; Svalbard; Ny Ålesund
• Online Access: https://doi.org/10.5194/acp-2019-610; https://www.atmos-chem-phys-discuss.net/acp-2019-610/

Low-level mixed-phase clouds (MPC) are common in the Arctic. Both local and large scale phenomena influence the properties and lifetime of MPC. 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 MPC in the fjord environment. In this work, we used a combination of ground-based remote sensing instruments, surface meteorological observations, radiosoundings, and reanalysis data to study persistent low-level MPC at Ny Ålesund, Svalbard, for a 2.5 year period. Methods to identify the cloud regime, surface coupling, as well as regional and local wind patterns were developed. We found that persistent 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 the overall mean of 35 and 12 g m −2 , respectively. 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. Furthermore, the near surface wind direction from the open sea was related to higher amounts of cloud liquid, and higher likelihood of coupling.We concluded that while the regional to large scale wind direction was important for the persistent MPC occurrence and its properties, also the local scale phenomena (local wind patterns in the fjord and surface coupling) 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.