Observations and simulation of a Saharan air layer event with a midtropospheric dust layer at Dakar, Senegal, 6-7 July 2010

Abstract

[1] On 3 July 2010 a large dust event was initiated over the Saharan Desert in Southern Algeria with the westward movement of an intensifying thermal low. Increases in Aerosol Optical Depth (AOD) in Algeria, Niger, Senegal and Cape Verde show the progression of the dust event with an AOD of 3.5 to 4 found in Senegal on 7 July. The surface total and direct shortwave radiative fluxes are reduced by more than 200 W m −2 and 300 W m −2 respectively compared to the previous day. Furthermore, there is an increase in diffuse shortwave radiation of 50-150 W m −2 when compared to the previous day. On 7 July, satellite based lidar observations confirm a uniform dust layer at approximately 5 km near the top of the Saharan Air layer where relative humidity values are greater than 50%. A WRF-GOCART simulation show additional sources of dust perturbed over Eastern and Western Mauritania during 6 and 7 July with elevated dust concentrations aloft in concert with satellite measurements on the morning of 7 July. The warm temperatures are associated with the thermal low creating sloping isentropes to the south, which allows the SAL air mass and dust aerosols to rise above the monsoon layer over Senegal.

Linkages between observed, modeled Saharan dust loading and meningitis in Senegal during 2012 and 2013

“…We have used WRF-Chem to simulate a large-scale summer dust event which was compared to ground measurements (Drame et al 2011). In order to simulate winter/spring Saharan dust events, the Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) module is used (Ginoux et al 2001).…”

“…The SAL may also inhibit tropical cyclone development through stable, dry air along with wind shear (Evan et al 2006) but may also influence convection within tropical cyclones through cloud-aerosol-microphysical interactions (Jenkins et al 2008). The SAL can be initiated by African Easterly Waves (AEWs), squall lines, or westward moving thermal lows (Jones et al 2008;Flamant et al 2007;Drame et al 2011).…”

“…Regional climate/weather models have successfully simulated large-scale winter and summer season dust events (Cavazos et al 2009;Drame et al 2011). However, these models have not been evaluated to examine simulated surface dust concentrations providing indications of air quality.…”

On the Importance of Aerosol Composition for Estimating Incoming Solar Radiation: Focus on the Western African Stations of Dakar and Niamey during the Dry Season

“…This decision was based on two reasons. First, aerosols in this region tend to travel west from Banizoumbou to Niamey [8] and therefore aerosol activity in Niamey is very similar to that in Banizoumbou with a small time shift [25]. Second, experiments conducted over Niamey in the present study would help to evaluate the possibility of using low resolution aerosol data in the operational estimation of surface fluxes.…”

“…Biomass-burning aerosols originating from anthropogenic activities [6] are mainly present during the dry season, between October and March [7]. Thus, both aerosol types may coexist in West Africa, resulting in aerosol optical depths (AOD) of 0.6 on average and up to 4 during strong dust storms [8].…”