Vertical structure and frequencies of deep convection during active periods of the West and Central African monsoon season

Abstract

Deep convective systems during active periods of the West African monsoon season have not been properly investigated over better temporal and spatial resolution in West Africa. Deep convective systems are investigated over seven climatic zones of the West African sub-region, which are as follows: west-coast rainforest, dry rainforest, Nigeria-Cameroon rainforest, Nigeria savannah, Central African and South Sudan (CASS) savannah, Sudano-Sahel, and Sahel, using data from Tropical Rainfall Measurement Mission (TRMM) Precipitation Feature (PF) database. The vertical structure of the convective systems indicated by the presence of at least one 40 dBZ and reaching (attaining) at least 1 km in the atmosphere showed strong core (highest frequency (%)) of reflectivity values around 2 km which is below the freezing level (4–5 km) for all the zones. Echoes are detected above the 15-km altitude much more frequently in the rainforest and Savannah zones than the Sudano and Sahel zones during active periods in March–May (MAM), whereas during active periods in June–September (JJAS), the savannahs, Sudano, and Sahel zone convections tend to reach higher altitude more frequently than the rainforest zones. The frequencies of deep convection defined by the presence of at least one 40 dBZ, reaching (attaining) at least 1 km in the atmosphere, with sizes greater than 2000 square, and having at least one convective pixels indicate that these systems are within the range of 2.3–2.8% in frequency averaged over the 16-year period of study in both March–May (MAM) and June–September (JJAS) active periods in the rainforest and savannah zones. These were found to be less than 2% in the Sudano and Sahel zones, except for the active JJAS period in Sudano zone.