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The influence of elevated smoke layers on stratocumulus clouds over the SE...

Das, S., N. Harshvardhan, and P. R. Colarco (2020), The influence of elevated smoke layers on stratocumulus clouds over the SE Atlantic in the NASA Goddard Earth Observing System (GEOS) model, J. Geophys. Res., 125, 1-20, doi:https://doi.org/10.1029/2019JD031209.

Previous evaluations of simulated aerosol transport over the south‐east Atlantic by globalaerosol models, including the Goddard Earth Observing System (GEOS) atmospheric general circulationmodel, showed that the bulk of the modeled smoke aerosol layer resided ~1–2 km lower than Cloud‐AerosolLidar with Orthogonal Polarization (CALIOP) lidar observations. Using this finding as the motivation,this study examines the changes in model‐simulated cloud properties in response to redistributing thevertical placement of the aerosol over the ocean. Ten years (2006–2015) of CALIOP‐retrieved smoke aerosolextinction profiles were used to redistribute the model‐simulated aerosol mass on a monthly mean basis,keeping the column aerosol mass conserved. The results from the model sensitivity experiments show thatelevating the aerosol layer to higher levels in agreement with CALIOP observations causes an increase incloud fractions by ~33% for shallow marine boundary layers (MBL) and a decrease by ~30% for deeper MBL.For a shallow MBL, aerosol‐induced warming within the cloud layers for the lower altitude aerosol casedecreases relative humidity at these levels and leads to a reduction of overall cloud amount compared to theelevated aerosol case. For a deeper MBL, however, aerosol heating within the upper cloud levels in the loweraltitude aerosol case increases the underlying MBL stability, which suppresses the cloud vertical extent,enhances cloud cover, and delays the stratocumulus to cumulus transition. Finally, aerosol redistributionimpacts on radiative forcing are investigated, which appear to be mainly driven by the changes in cloud areafractions rather than in‐cloud liquid water path changes between the model experiments.

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Atmospheric Composition
Radiation Science Program (RSP)