Thursday, 25 May 2000: 4:30 PM
Sahel rainfall exhibits a clear decadal signal with a period of above normal
rainfall
in the 50s and 60s and a long stretch of dryness that began in 1972. The 1999
Sahel
rainfall season was the wettest since 1972, but only the 10th wettest since
1950.
NCEP/NCAR reanalysis data and OI SST data are used to assess the Sahel rainfall
during the 1999 season. The influence of the cold ENSO event is addressed. It
is
shown in particular that strong low level velocity convergence was present in
the
Gulf of Guinea region associated with a well defined African Easterly Jet (AEJ)
exhibiting a clear axis centered around 15N. This axis of the AEJ was located
at the
equatorward flank of the cyclonic shear zone where much of the African waves
and
their associated cloud systems developed. It is also shown that the Tropical
Easterly Jet (TEJ) was well defined and extended well into the Atlantic Ocean.
Predictions for the Sahel rainfall at one month lead based on CCA and using
global
SSTs as predictor field were also made and verified against observations.
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