| dc.description.abstract | The precipitation associated with atmospheric circulations in summer, over West
Africa shows large intraseasonal and interannual variability. The changes in the
circulation characteristics were of importance, as they contributed significantly to
the interseasonal variability of the rainfall. The NCEP-NCAR reanalysis dataset
were used to investigate the wind field, vorticity term, stability index, precipitable
water, moisture term, depth of convectively geopotential, and precipitation for
August and September for the period 1984-2004.
In the present study, dynamic and thermodynamic characteristics of the
atmosphere associated with summer rainfall during wet and dry periods were
investigated. Rainfall was examined using a 500-station archive. The vorticity,
moisture budget, and moist static energy were analyzed between 850 and
200hPa in Auqust and September for 1984 (dry year) and 2004 (wet year).
Significant changes in the wind and vorticity fields at 850hpa and 200hpa took
place over the sub-region of West Africa. A large magnitude stability indices,
strong monsoon circulation, and wet condition over the Sahel region were
observed in August of 2004; and on the other hand, small magnitude stability
indices, very weak circulation; and relatively dry condition were observed in the
same month for 1984. However, in' September the value of stability index was
smaller and hence a reduced activity of monsoon circulation and low rainfall was
observed during the period | en |
