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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 5 | Copyright
Atmos. Chem. Phys., 16, 2877-2900, 2016
https://doi.org/10.5194/acp-16-2877-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 04 Mar 2016

Research article | 04 Mar 2016

Shortwave direct radiative effects of above-cloud aerosols over global oceans derived from 8 years of CALIOP and MODIS observations

Zhibo Zhang1,2, Kerry Meyer3,4, Hongbin Yu3,5, Steven Platnick3, Peter Colarco3, Zhaoyan Liu6,7, and Lazaros Oreopoulos3 Zhibo Zhang et al.
  • 1Physics Department, University of Maryland Baltimore County (UMBC), Baltimore, Maryland, USA
  • 2Joint Center of Earth System Technology (JCET), UMBC, Baltimore, Maryland, USA
  • 3NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 4Goddard Earth Science Technology and Research (GESTAR), Universities Space Research Association, Columbia, Maryland, USA
  • 5Earth System Science Interdisciplinary Center (ESSIC), University of Maryland, College Park, Maryland, USA
  • 6Science Systems and Applications, Inc. (SSAI), Lanham, Maryland, USA
  • 7NASA Langley Research Center, Hampton, Virginia, USA

Abstract. In this paper, we studied the frequency of occurrence and shortwave direct radiative effects (DREs) of above-cloud aerosols (ACAs) over global oceans using 8 years (2007–2014) of collocated CALIOP and MODIS observations. Similar to previous work, we found high ACA occurrence in four regions: southeastern (SE) Atlantic region, where ACAs are mostly light-absorbing aerosols, i.e., smoke and polluted dust according to CALIOP classification, originating from biomass burning over the African Savanna; tropical northeastern (TNE) Atlantic and the Arabian Sea, where ACAs are predominantly windblown dust from the Sahara and Arabian deserts, respectively; and the northwestern (NW) Pacific, where ACAs are mostly transported smoke and polluted dusts from Asian. From radiative transfer simulations based on CALIOP–MODIS observations and a set of the preselected aerosol optical models, we found the DREs of ACAs at the top of atmosphere (TOA) to be positive (i.e., warming) in the SE Atlantic and NW Pacific regions, but negative (i.e., cooling) in the TNE Atlantic Ocean and the Arabian Sea. The cancellation of positive and negative regional DREs results in a global ocean annual mean diurnally averaged cloudy-sky DRE of 0.015Wm−2 (range of −0.03 to 0.06Wm−2) at TOA. The DREs at surface and within the atmosphere are −0.15Wm−2 (range of −0.09 to −0.21Wm−2), and 0.17Wm−2 (range of 0.11 to 0.24Wm−2), respectively. The regional and seasonal mean DREs are much stronger. For example, in the SE Atlantic region, the JJA (July–August) seasonal mean cloudy-sky DRE is about 0.7Wm−2 (range of 0.2 to 1.2Wm−2) at TOA. All our DRE computations are publicly available1. The uncertainty in our DRE computations is mainly caused by the uncertainties in the aerosol optical properties, in particular aerosol absorption, the uncertainties in the CALIOP operational aerosol optical thickness retrieval, and the ignorance of cloud and potential aerosol diurnal cycle. In situ and remotely sensed measurements of ACA from future field campaigns and satellite missions and improved lidar retrieval algorithm, in particular vertical feature masking, would help reduce the uncertainty.

1 https://drive.google.com/folderview?id=0B6gKx4dgNY0GMVYzcEd0bkZmRmc&usp=sharing

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The frequency of occurrence and shortwave direct radiative effects (DRE) of above-cloud aerosols (ACAs) over global oceans are investigated using 8 years of collocated CALIOP and MODIS observations. We estimated that ACAs have a global ocean annual mean diurnally averaged cloudy-sky DRE of 0.015 W m−2 (range of −0.03 to 0.06 W m−2) at TOA. The DREs at surface and within atmosphere are −0.15 W m−2 (range of −0.09 to −0.21 W m−2), and 0.17 W m−2 (range of 0.11 to 0.24 W m−2), respectively.
The frequency of occurrence and shortwave direct radiative effects (DRE) of above-cloud aerosols...
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