Inter annual variability of medium level circulation and Its association with seasonal rainfall over equatorial East Africa.

Abstract

This study was an attempt to explore the role of atmospheric circulation and its predictive association or linkage with seasonal rainfall over Equatorial Eat Africa. The data used in the study included the NCEP/NCAR reanalysis wind data, the CRU global rainfall data and station rainfall data for the three East African countries comprising Kenya, Uganda and Tanzania. The study period extended from 1961-1998. In order to assess the association between atmospheric circulation and the seasonal rainfall over the domain of this study, statistical methods were adopted. These included quality control, standardization of anomaly indices and correlation analysis. Results from the quality control tests indicated that the data used in the study were of good quality. The standardized rainfall data were used to compare the year to year rainfall patterns. It was evident from the normalized rainfall indices that occurrences of droughts and floods are common over East Africa and that some of the extreme rainfall events coincide with certain phases of the zonal wind, the u component. The correlation between the u wind component and the seasonal rainfall index during the short rainfall season over the area 40oE-50oE; 5~-5°S was significant. It was concluded from the study that there is a possible linkage between the OND rainfall index and the u wind component over the location 40oE-50oE; 5~-5°S within the area of study. Such information will help improve monitoring, prediction and early warning of extreme rainfall events over the region of study. It was also concluded from the predictive potentials of the study that the month of January could be used to predict the long rainfall season. However the short rainfall season did not show any predictive potential.