Convective available potential energy (CAPE) in Northern Africa and tropical Atlantic and study of its connections with rainfall in Central and West Africa during Summer 1985

Abstract

In this paper, we study the distribution of the convective available potential energy (CAPE) in northern Africa and tropical Atlantic in summer. The pattern of this parameter is quite steady and presents three main zones. The first one is located between the equator and 15°N–20°N, with positive values of CAPE. In the second and the third zones located north of the band of latitudes 15°N–20°N and south of the equator, respectively, CAPE has negative values. We examined, in some details, the main tendencies of the CAPE pattern inside the first zone (CAPE >0, in general) and we compared them to the rainfall pattern. We noted that the CAPE pattern in this zone presents three regions of maximum values: west, center, and east of the zone. The maximum at east and the maximum in the center seem to be connected to the orography effects. Between 15°N and 20°N, the CAPE distribution is characterised by its iso-line zero. This iso-line zero seems to define the north limit of the inter tropical convergence zone (ITCZ). In fact, the position of the iso-line zero on the CAPE distribution fluctuates during summer as the position of the ITCZ so that this parameter can also be used as a parameter or an index to define the ITCZ position in northern Africa and tropical Atlantic in the summer. The patterns of the rainfall and CAPE in this zone (5°N–20°N) have a very good similarity. When the rainfall is very weak (<2 mm day −1) towards 12.5°N–15°N, the CAPE tends to become zero. The rainfall pattern presents, in general, high values towards Guinea and around Lake Chad. These regions are not very far from the maximum values of CAPE observed in different figures. The fields of correlation coefficients between the two parameters show that the rainfall and the CAPE are very well correlated around the ITCZ and towards some mountains. So, the strong values of the correlation coefficients seem to indicate that each of these two parameters is influenced by the ITCZ effects and by the orography effects.