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contributor authorAdebiyi, Adeyemi A.
contributor authorZuidema, Paquita
contributor authorAbel, Steven J.
date accessioned2017-06-09T17:10:40Z
date available2017-06-09T17:10:40Z
date copyright2015/03/01
date issued2014
identifier issn0894-8755
identifier otherams-80623.pdf
identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4223536
description abstractiomass burning aerosols seasonally overlie the subtropical southeast Atlantic stratocumulus deck. Previous modeling and observational studies have postulated a semidirect effect whereby shortwave absorption by the aerosol warms and stabilizes the lower troposphere, thickening the low-level clouds. The focus herein is on the dynamical and moisture effects that may be convoluted with the semidirect effect. Almost-daily radiosonde data from remote St. Helena Island (15.9°S, 5.6°W), covering September?October 2000?11, are combined with daily spatial averages (encompassing the island) of the MODIS clear-sky fine-mode aerosol optical depth . Increases in are associated with increases in 750?500-hPa moisture content. The net maximum longwave cooling by moisture of almost 0.45 K day?1 reduces the aerosol layer warming from shortwave absorption. ERA-Interim spatial composites show that polluted conditions are associated with a strengthening of a deep land-based anticyclone over southern Africa, facilitating the westward offshore transport of both smoke and moisture at 600 hPa. The shallower surface-based South Atlantic anticyclone exhibits a less pronounced shift to the northeast, strengthening the low-level coastal jet exiting into the stratocumulus deck and cooling 1000-hPa potential temperatures. Warm continental outflow further increases the 800-hPa potential temperatures , reinforcing the lower tropospheric stability over the stratocumulus deck. Enhanced southerly dry air advection also strengthens the cloud-top humidity inversion. The increased stability helps explain an observed decrease in cloud-top heights despite an anomalous reduction in subsidence. The changes to the horizontal dynamics enhance low-level cloudiness. These are separate but not necessarily distinct from an aerosol semidirect effect, encouraging care in attribution studies.
publisherAmerican Meteorological Society
titleThe Convolution of Dynamics and Moisture with the Presence of Shortwave Absorbing Aerosols over the Southeast Atlantic
typeJournal Paper
journal volume28
journal issue5
journal titleJournal of Climate
identifier doi10.1175/JCLI-D-14-00352.1
journal fristpage1997
journal lastpage2024
treeJournal of Climate:;2014:;volume( 028 ):;issue: 005
contenttypeFulltext


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