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Simulation of Aerosol Indirect Effects on Cloud Streets Over the Northwestern Pacific Ocean
Author(s) -
Wu ChungKai,
Chen JenPing
Publication year - 2021
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2020jd034325
Subject(s) - aerosol , drizzle , environmental science , atmospheric sciences , liquid water content , cloud albedo , entrainment (biomusicology) , sea salt aerosol , liquid water path , troposphere , cloud top , meteorology , plume , boundary layer , cloud computing , climatology , cloud cover , precipitation , geography , geology , philosophy , physics , aesthetics , sea salt , computer science , rhythm , operating system , thermodynamics
We simulated aerosol effects on cloud streets formed during continental cold‐air outbreaks over the Northwestern Pacific using an aerosol‐sensitive cloud microphysical scheme coupled with the Weather Research and Forecast model. The micro‐ and macro‐scale responses were examined under a wide range of aerosol concentrations. The cloud streets generally remain in a transient state, indicating that the aerosol particles may significantly affect the cloud system's development. The simulation results revealed a clear Twomey effect, but they were contrary to some of the Albrecht effect, especially under relatively clean conditions. Such reversed Albrecht effects stem mainly from dynamic response to changes in atmospheric stability associated with drizzle evaporation in the sub‐cloud layer. The dynamic response works against thermal forcing from the large air‐sea temperature gradient in a cold‐air outbreak. As the aerosol increases, the drizzle mechanisms weaken, and the boundary layer becomes more convective, leading to stronger dry‐air entrainment from the free troposphere. In individual clouds, the effect of entrainment on cloud water content may be compensated by more substantial vertical vapor flux. These mechanisms lead to a reduction in the cloud amount. Furthermore, the reduced moisture flux from drizzle evaporation in the sub‐cloud layer, as well as the reduced sedimentation speed of the smaller cloud drops, tend to lessen cloud thickness. The overall reduction in cloud dimensions may offset the Twomey effect by up to 20% in cloud albedo.