Abstract
The need to investigate diurnal weather cycles in West Africa originates from the fact that complex interactions often result between mesoscale and synoptic weather processes. This study investigates diurnal cycles of rainfall and convective properties using six (6) hour interval data from the ERA-Interim and derived products from the Tropical Rainfall Measurement Mission (TRMM). Results showed that the land-ocean warming contrast is more strongly sensitive to the seasonal cycle, being very weak during March-May (MAM) but clearly spelled out during June-September (JJAS). Dipoles of wind convergence/divergence and wet/dry precipitation, between CASS and Nigeria Savannah zones, were identified in the morning and evening hours of MAM, whereas distinct night and day anomalies, same location in CASS, were found to be consistent during the JJAS season. The locations of flash count and system sizes agree with the climatology of convective properties, that morning and day-time hours are dominated by stratiform precipitation and small system sizes. Most results clearly showed that the eastern locations of Sudano and Sahel are consistently dry because rainfall and precipitation features are predominantly few. Very unique results about the dipole of wind and precipitation between two zones and the unusual dry zones of Sudan and Sahel have been found. Results presented had shown the importance of diurnal variation in understanding precipitation, flash count, system sizes patterns at diurnal scales, and understanding land-ocean contrast, precipitation and wind field anomaly at diurnal scales.
Highlights
Flash count is most frequent during the day (12 Z) and evening (18 Z) periods in both MAM and JJAS season (([25] [26]). This is a clue that convective and Mesoscale Convective systems could be more dominant during the day and evening periods whereas stratiform precipitation is dominant during the night and morning periods
This research work investigated the diurnal variation of rainfall and two convective properties at six (6) hour intervals
Systems with an extremely large number of Flashcount and system sizes were dominant during day-time (12 Z) and evening periods (18 Z) than other diurnals in both MAM and JJAS, whereas systems with extremely few Flashcounts were dominant during morning diurnals, which constituted most of the stratiform precipitation in the morning diurnals
Summary
In tropical West Africa (near the Guinea Coast) deep convection in the boreal summer has been found to develop in the late afternoon and reaches a maximum. In the semi-arid regions of the Sahel convection has been found to initiate in the evening, with peak precipitation rates occurring in the early morning ([4] [5]) This is similar to results by [6] that westward propagating storms in the Equatorial regions of the Rift Valley, Lake Victoria and part of the Congo Forest tend high precipitation rates. In West Africa, MCSs are often triggered by elevated daytime heating and orography [7] These storms typically propagate westward away from their source regions, such that the timing of peak precipitation occurs later and later as the MCS moves farther and farther away from its source region [8]. The authors aim to investigate diurnal pattern/distribution and characteristics of convective properties
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