Spatio‐temporal variability of cloud cover types in West Africa with satellite‐based and reanalysis data

Abstract

This study aims to understand and document the occurrence and variability of cloud cover types in West Africa (WA). Investigations are carried out with a 10‐year hourly record of two cloud data products: CERES passive satellite observations and ERA5 reanalysis. The seasonal evolutions of high (HCC), middle (MCC), low (LCC) and total (TCC) cloud cover are examined. Both products agree on the seasonal and spatial occurrence of cloud cover, although CERES presents lower values of cloud fraction than ERA5 which is partly attributed to the inability of the satellite sensor to detect optically thin clouds in the atmosphere. Southern WA is found to be cloudier than other parts of the region in all seasons with mean TCC fractions of 70 and 80% for CERES and ERA5 respectively during the monsoon season. In all seasons, the presence of LCC over large areas of the Sahel/Sahara region is noted in the CERES product. This could be due to a possible misinterpretation of Saharan dust as low clouds which may have thus, caused it to overestimate the occurrences and fractions of LCC over this region. Northern WA is associated with higher frequencies of no cloud occurrence events, unlike the south where cloudless skies are rarely observed. Furthermore, in southern WA, overcast conditions of LCC are observed for a significant number of times (up to 20% of the time during the rainy season in CERES and 40% in ERA5). The climatology of cloud cover presented in this study could be useful for the planning of solar energy projects.

Cloudiness Information Services for Solar Energy Management in West Africa

“…Although the Senegal window is located in the Sahel region of WA, its proximity to the ocean (similar to the Cote d'Ivoire window) could lead to increased cloudiness compared to the other two Sahelian windows [30]. No window is located north of latitude 16 • N, because this area is usually characterized by very low cloud coverage throughout the year [18,19].…”

“…Atmosphere 2020, 11, x FOR PEER REVIEW 4 of 18 the region obtained from the Integrated Surface Database [25]. The comparison showed a satisfactory agreement between the reanalysis and in situ dataset (see Appendix S1 in [19]). Here, we evaluate the surface downwelling shortwave radiation flux with in situ observations in WA.…”

“…A necessary condition for using the ERA5 dataset for such a study is to first evaluate its ability to reproduce the actual observations in the region of interest. In a recent study by [19] in WA, the ERA5 cloud fraction was compared with some synoptic in situ observations (and satellite data) from the region obtained from the Integrated Surface Database [25]. The comparison showed a satisfactory agreement between the reanalysis and in situ dataset (see Appendix S1 in [19]).…”

“…In a recent study by [19] in WA, the ERA5 cloud fraction was compared with some synoptic in situ observations (and satellite data) from the region obtained from the Integrated Surface Database [25]. The comparison showed a satisfactory agreement between the reanalysis and in situ dataset (see Appendix S1 in [19]). Here, we evaluate the surface downwelling shortwave radiation flux with in situ observations in WA.…”

“…The climate of WA, which is controlled by the West African Monsoon, is typically characterized by an intense coverage of different cloud types [17,18] associated with a high spatial-temporal variability [19]. However, the impacts of these clouds on the incoming solar radiation needed for power generation are not very well studied in the region.…”