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| Titel |
A novel method for estimating shortwave direct radiative effect of above-cloud aerosols using CALIOP and MODIS data |
| VerfasserIn |
Z. Zhang, K. Meyer, S. Platnick, L. Oreopoulos, D. Lee, H. Yu |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 7, no. 6 ; Nr. 7, no. 6 (2014-06-19), S.1777-1789 |
| Datensatznummer |
250115823
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| Publikation (Nr.) |
 copernicus.org/amt-7-1777-2014.pdf |
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| Zusammenfassung |
| 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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