Numerical simulation of land and sea-breeze (LSB) circulation along the Guinean Coast of West Africa

Abstract

This study uses both observed and simulated data to investigate the diurnal evolution of land and sea-breeze (LSB) circulation across the Guinean Coast of West Africa. Numerical simulations, with ERA-Interim and CFS as forcing data, were carried out using a modified WRF-ARW model code to evaluate the model’s ability to capture the LSB kinematics over West Africa. Two simulation runs were performed with each data set. Comparison of the simulated and observed winds showed that the WRF model was able to capture the rotation of LSB in the coastal areas of the region very well. Results also showed that the simulated diurnal evolutions of the hodographs and onshore/offshore winds were found to be in good agreement with the observations. Furthermore, the simulations showed complex patterns of clockwise (CR) and anti-clockwise rotations (ACR) across the Guinean Coast. The sense of rotation is a result of complex interaction between surface and synoptic pressure gradients, horizontal and vertical diffusion, and advection terms. Overall, the results of the analysis showed that the balance is not always dominated by the pressure gradient terms, as suggested by earlier studies. However, hourly analysis of the rotation terms strongly indicates that over the ocean, surface pressure gradients dominate, while diffusion terms are more important over land areas. The Coriolis term was found not to be significant, the study area being close to the equator. Significantly, regions over water are found to be dominated by ACR, while land areas showed more CR. This may be attributed to the variation of surface roughness due to the landscape and urbanization.