Long-Term Variation of Sunshine Duration and Their Inter-Action with Meteorogical Parameters over Chad, Central Africa

摘要

This study aims to evaluate the long-term variations of sunshine duration and to estimate its interaction with meteorogical parameters from 1950 to 2010 in Chad, Central Africa. The results show that Chad is the one of world’s sunniest countries. Each year, Chad receives more than 3030.91 ± 176.33 hours of sunning corresponding to 8.9 hours daily. Likewise, a strong north-south gradient is noted over Chad. For instance, the daily insolation is 10 ± 0.41 hours in the north, 8.85 ± 1.1 hours in the center and 7.75 ± 1.8 hours in the south. Furthermore, there is a marked seasonality of sunshine duration with maximums in dry season and minimums during the rainy season. The lowest values of sunshine duration are found in August. On the contrary, maximums are recorded from November to February with values greater than 9.5 hours per day. Moreover, the annual anomalies study allowed determining three great periods in terms of sunshine variability in Chad. Firstly, the period between 1950 to 1970 (named humid period) is characterized by the lowest values of sunshine duration in Chad. Secondly, from 1970 and 1990, the region suffered an unprecedented drought which resulted in an increase of sunstroke duration in Chad. And finally, the period from 1990 to 2010 called the return period is characterized by a rapid year-to-year fluctuations of insolation duration. Unlike to surface temperature, we have also shown that there is a direct relation between the duration of insolation and the meteorological parameters such as precipitations and relative humidity.