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Determination of Radiative Forcing of Saharan Dust using Combined TOMS and ERBE DataThe direct radiative forcing of Saharan dust aerosols has been determined by combining aerosol information derived from Nimbus-7 TOMS with radiation measurements observed at the top of atmosphere (TOA) by NOAA-9 ERBE made during February-July 1985. Cloud parameters and precipitable water derived from the NOAA-9 HIRS2 instrument were used to aid in screening for clouds and water vapor in the analyses. Our results indicate that under "cloud-free" and "dry" conditions there is a good correlation between the ERBE TOA outgoing longwave fluxes and the TOMS aerosol index measurements over both land and ocean in areas under the influence of airborne Saharan dust. The ERBE TOA outgoing shortwave fluxes were also found to correlate well with the dust loading derived from TOMS over ocean. However, the calculated shortwave forcing of Saharan dust aerosols is very weak and noisy over land for the range of solar zenith angle viewed by the NOAA-9 ERBE in 1985. Sensitivity factors of the TOA outgoing fluxes to changes in aerosol index were estimated using a linear regression fit to the ERBE and TOMS measurements. The ratio of the shortwave-to-longwave response to changes in dust loading over the ocean is found to be roughly 2 to 3, but opposite in sign. The monthly averaged "clear-sky" TOA direct forcing of airborne Saharan dust was also calculated by multiplying these sensitivity factors by the TOMS monthly averaged "clear-sky" aerosol index. Both the observational and theoretical analyses indicate that the dust layer height, ambient moisture content as well as the presence of cloud all play an important role in determining the TOA direct radiative forcing due to mineral aerosols.
Document ID
19990100663
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Hsu, N. Christina (Raytheon STX Corp. Lanham, MD United States)
Herman, Jay R. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Weaver, Clark (SM and A Corp. Arlington, VA United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1999
Subject Category
Meteorology And Climatology
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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