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Satellite-derived interannual variability of West African rainfall during 1983-88Two satellite algorithms for rain estimation are used to study the interannual variability of West African rainfall during contrasting years of the period 1983-88. The first algorithm uses a frequency of occurrence index quantifying the number of times Meteosat thermal infrared radiance below 2.107 W/sq m/sr/micrometer (-40 C) occurs during the rainy season. The second algorithm uses the average Meteosat thermal infrared radiance over the period of interest. Appropriate calibrations are performed using these satellite parameters and ground-based rainfall observations. Separate calibration and equations are considered for each of three suggested subrainfall zones in West Africa: two Sahelian zones located just north of 9 deg N (one east and one west of 5 deg W) and the region extending south from 9 deg N to the coast. Over 80% of the variance in the ground-based rainfall data is explained by both algorithms in regions located north of 9 deg N, but poor correlations between observed and estimated rainfall exist south of 9 deg N. The interannual variability of rainfall in the Sahel is well described by that of cold clouds and average radiances. The satellite estimates also reveal substantial longitudinal variability in the anomaly fields, indicating that some Sahelo-Soudanian areas may receive above average rainfall during a year cataloged as dry. The latitudinal displacement and the extent of the cloud band associated with the intertropical convergence zone (ITCZ), as derived from cold cloud indices, indicate a northward displacement of the ITCZ in some, but not all, wet years in the Sahel. No systematic anomalous southward displacement of the ITCZ is evident in dry years. Drought in the Sahel appears to be more closely linked to the lattitudinal extent and the intensity of the convection within the ITCZ.
Document ID
19950047984
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Ba, Mamoudou B.
(Scripps Institution of Oceanography, La Jolla, CA United States)
Frouin, Robert
(Scripps Institution of Oceanography, La Jolla, CA United States)
Nicholson, Sharon E.
(The Florida State University Tallahassee, FL, United States)
Date Acquired
August 16, 2013
Publication Date
February 1, 1995
Publication Information
Publication: Journal of Applied Meteorology
Volume: 34
Issue: 2
ISSN: 0894-8763
Subject Category
Meteorology And Climatology
Accession Number
95A79583
Funding Number(s)
CONTRACT_GRANT: NAG5-1587
CONTRACT_GRANT: NAGW-1968
Distribution Limits
Public
Copyright
Other

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