Climatology of Satellite-Derived Mesoscale Convective Systems over West Africa

Abstract

This work studied the climatology of Mesoscale Convective Systems (MCSs) over West Africa. Infrared brightness temperature (BT) data was collected from Tropical Rainfall Measuring Mission (TRMM) website over the rainy season period for ten years (2006 - 2015) from 1^st of June to 30^th of September. The study area covers West Africa from 5ºS to 25ºN and 20ºE to 20ºW, it was divided to 5^o X 5^o boxes. The T-R criteria used to detect the minimum size of MCSs was a diameter of 200 km or more and a BT of 233 K (-40 ºC) or less. All the MCSs were tracked for the months of June, July, August and September and compared the wettest (2014) and the driest (2009) years as observed from the ten years annual rainfall data collected from the archives of the Nigerian Meteorological Agency (NIMET). The results indicated that for both the driest and wettest years, latitudinal row 5ºN - 10ºN is the most active zone favorable for the initiation, propagation and decay of MCSs over West Africa with 45% of MCSs found there in the month of June and row 10ºN - 15ºN as the next favorable zone (29-32% of MCSs). In the month of July, the active zone shifted to 10ºN - 15ºN while the next favorable zone also shifted to 5ºN - 10ºN, which was maintained and became more favorable through August and September. There were almost double the number of MCSs occurrence in the wettest year compared to driest year. During wettest year, MCSs were found out to be slower than their driest year counterpart. The results also gave a better insight of the behavioral patterns of West African MCSs, hence improving general forecasting method and reliability.

Keywords: active zone, initiation, propagation, DETRAWACS, tracking.