Interaction Of Mesoscale Convective Systems With The Land – Sea Breezes Along The Guinea Coast Of West Africa

Abstract:

1-3 hourly METARS/SYNOP observation data of wind (speed and direction), air temperature over land, covering the period 1983-2012, were used in order to characterize land-sea breezes (LSB) over five coastline stations (Abidjan, Accra, Lomé, Cotonou and Ikeja-Lagos) in the Guinean Coast, West Africa. In additional to this, 8 years (2003-2010) sea surface temperature (SST) data from adjacent Atlantic Ocean and monthly METARS/SYNOP observation data of precipitation (1983-2012) were also used. Based on wind speed and direction, the wind roses of all months over all stations have been plotted. These wind roses reveal that, globally, the northerly winds occurred rarely for the months of February, March, and April at Cotonou (Benin Republic).This is seen for other stations (Lomé and Accra). The night/morning time northerly winds appear at all stations, except Accra where there is no northerly wind or is very weak. According to the stations basis, the period of that night/morning northerly winds varies, except in summer period (July – September), where the normal s/w monsoon winds can weaken override at all stations. Set criteria based on the diurnal reversal of wind direction, and the thermal gradient necessary to drive the wind circulation, was used to identify land-sea breeze days. On station-wide basis, sea-breezes occur, at least all period of year, but less frequent in the summer months, where the minimum value of monthly mean temperature gradient is observed for selected stations.