Large-Eddy Simulations of Marine Boundary Layer Clouds Associated with Cold-Air Outbreaks during the ACTIVATE Campaign. Part II: Aerosol–Meteorology–Cloud Interaction
Xiangyu Li, Hailong Wang, Jingyi Chen, Satoshi Endo, Simon Kirschler, Christiane Voigt, Ewan Crosbie, Luke D. Ziemba, David Painemal, Brian Cairns, Johnathan W. Hair, Andrea F. Corral, Claire Robinson, Hossein Dadashazar, Armin Sorooshian, Gao Chen, R. A. Ferrare, Mary M. Kleb, Hongyu Liu, Richard H. Moore, Amy Jo Scarino, Michael A. Shook, Taylor Shingler, Kenneth L. Thornhill, Florian Tornow, Heng Xiao, Xubin Zeng
Abstract
Abstract Aerosol effects on micro/macrophysical properties of marine stratocumulus clouds over the western North Atlantic Ocean (WNAO) are investigated using in situ measurements and large-eddy simulations (LES) for two cold-air outbreak (CAO) cases (28 February and 1 March 2020) during the Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE). The LES is able to reproduce the vertical profiles of liquid water content (LWC), effective radius r eff and cloud droplet number concentration N c from fast cloud droplet probe (FCDP) in situ measurements for both cases. Furthermore, we show that aerosols affect cloud properties ( N c , r eff , and LWC) via the prescribed bulk hygroscopicity of aerosols ( ) and aerosol size distribution characteristics. N c , r eff , and liquid water path (LWP) are positively correlated to and aerosol number concentration ( N a ) while cloud fractional cover (CFC) is insensitive to and aerosol size distributions for the two cases. The realistic changes to aerosol size distribution (number concentration, width, and the geometrical diameter) with the same meteorology state allow us to investigate aerosol effects on cloud properties without meteorological feedback. We also use the LES results to evaluate cloud properties from two reanalysis products, ERA5 and MERRA-2. Compared to LES, the ERA5 is able to capture the time evolution of LWP and total cloud coverage within the study domain during both CAO cases while MERRA-2 underestimates them.