Variability of Total Latent Heating Rate over Three Climatic Zones in West Africa

Abstract

A study of variability of latent heating rate over West Africa has been done. Results were divided into three categories: mean latent heating rate profiles, monthly time series of mean latent heating rate at four different vertical layers in the atmosphere, and the latitudinal cross section of the mean 4 – 11 km diurnal latent heat distribution. The data was analysed using seventeen (17) years Tropical Rainfall measurement mission (TRMM) Precipitation Radar (PR) data, of total (convective + stratiform) latent heating, over West Africa. Strong latent heating rate was observed in the Savannah zone than Guinea and Sahel zones during MAM season, whereas in the JJAS season, latent heating rate was much weaker when compared to MAM season. In JJAS season, the Sahel zone indicated stronger latent heating rate than the other two zones. Sahel had the weakest latent heating rate in MAM, whereas Guinea had the weakest latent heating rate in JJAS. The first vertical layer (0.5 – 3 km) indicated that latent heating rate dropped sharply in April and August, and there are also bi – modal peak in June and September. With altitude, the bi – modal distribution is sustained in the Savannah zone, but Guinea and Sahel zones gradually change to one – mode. At higher layers, results indicated that Guinea and Sahel are always showing contrasting modes, especially around August.  The 4- 11 km diurnal pattern showed that, during MAM, peak occurrence of latent heating rate is mostly observed during 16 – 23 hours, that is, late in the evening hours. In the case of JJAS, these observed strong latent heating rate are now located above latitude 80N, but occurrence of peak values are sustained at evening hours.