References

AMT

Atmospheric Measurement Techniques

AMT

Atmos. Meas. Tech.

1867-8548

Copernicus Publications

Göttingen, Germany

10.5194/amt-7-1777-2014

A novel method for estimating shortwave direct radiative effect of above-cloud aerosols using CALIOP and MODIS data

Zhang

https://orcid.org/0000-0001-9491-1654

¹ ² Meyer

³ ⁴ Platnick

https://orcid.org/0000-0003-3964-3567

⁴ Oreopoulos

⁴ Lee

⁴ ⁵ Yu

⁴ ⁶

Department of Physics, University of Maryland, Baltimore County (UMBC), Baltimore, MD, USA

Joint Center Earth Systems & Technology (JCET), UMBC, Baltimore, MD, USA

Goddard Earth Sciences Technology and Research (GESTAR), Universities Space Research Association, Columbia, MD, USA

NASA Goddard Space Flight Center, Greenbelt, MD, USA

Goddard Earth Sciences Technology and Research (GESTAR), Morgan State University, Baltimore, MD, USA

Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA

19 06 2014

7 6 1777 1789

2014

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

This article is available from https://amt.copernicus.org/articles/7/1777/2014/amt-7-1777-2014.html

The full text article is available as a PDF file from https://amt.copernicus.org/articles/7/1777/2014/amt-7-1777-2014.pdf

This paper describes an efficient and unique method for computing the shortwave direct radiative effect (DRE) of aerosol residing above low-level liquid-phase clouds using CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) and MODIS (Moderate Resolution Imaging Spectroradiometer) data. It addresses the overlap of aerosol and cloud rigorously by utilizing the joint histogram of cloud optical depth and cloud top pressure while also accounting for subgrid-scale variations of aerosols. The method is computationally efficient because of its use of grid-level cloud and aerosol statistics, instead of pixel-level products, and a precomputed look-up table based on radiative transfer calculations. We verify that for smoke and polluted dust over the southeastern Atlantic Ocean the method yields a seasonal mean instantaneous (approximately 13:30 local time) shortwave DRE of above-cloud aerosol (ACA) that generally agrees with a more rigorous pixel-level computation within 4%. We also estimate the impact of potential CALIOP aerosol optical depth (AOD) retrieval bias of ACA on DRE. We find that the regional and seasonal mean instantaneous DRE of ACA over southeastern Atlantic Ocean would increase, from the original value of 6.4 W m−2 based on operational CALIOP AOD to 9.6 W m−2 if CALIOP AOD retrievals are biased low by a factor of 1.5 (Meyer et al., 2013) and further to 30.9 W m−2 if CALIOP AOD retrievals are biased low by a factor of 5 as suggested in Jethva et al. (2014). In contrast, the instantaneous ACA radiative forcing efficiency (RFE) remains relatively invariant in all cases at about 53 W m−2 AOD−1, suggesting a near-linear relation between the instantaneous RFE and AOD. We also compute the annual mean instantaneous shortwave DRE of light-absorbing aerosols (i.e., smoke and polluted dust) over global oceans based on 4 years of CALIOP and MODIS data. We find that given an above-cloud aerosol type the optical depth of the underlying clouds plays a larger role than above-cloud AOD in the variability of the annual mean shortwave DRE of above-cloud light-absorbing aerosol. While we demonstrate our method using CALIOP and MODIS data, it can also be extended to other satellite data sets.

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