The climatology of dust aerosol over the arabian peninsula

Abstract. Dust storms are considered to be a natural hazard over the Arabian Peninsula, since they occur all year round with maximum intensity and frequency in Spring and Summer. The Regional Climate Model version 4 (RegCM4) has been used to study the climatology of atmospheric dust over the Arabian Peninsula from 1999 to 2012. This relatively long simulation period samples the meteorological conditions that determine the climatology of mineral dust aerosols over the Arabian Peninsula. The modeled Aerosol Optical Depth (AOD) has been compared against ground-based observations of three Aerosol Robotic Network (AERONET) stations that are distributed over the Arabian Peninsula and daily space based observations from the Multi-angle Imaging SpectroRadiometer (MISR), the Moderate resolution Imaging SpectroRadimeter (MODIS) and Ozone Monitoring Instrument (OMI). The large scale atmospheric circulation and the land surface response that lead to dust uplifting have been analyzed. While the modeled AOD shows that the dust season extends from March to August with two pronounced maxima, one over the northern Arabian Peninsula in March with AOD equal to 0.4 and one over the southern Arabian Peninsula in July with AOD equal to 0.7, the observations show that the dust season extends from April to August with two pronounced maxima, one over the northern Arabian Peninsula in April with AOD equal to 0.5 and one over the southern Arabian Peninsula in July with AOD equal to 0.5. In spring a high pressure dominates the Arabian Peninsula and is responsible for advecting dust from southern and western part of the Arabian Peninsula to northern and eastern part of the Peninsula. Also, fast developed cyclones in northern Arabian Peninsula are responsible for producing strong dust storms over Iraq and Kuwait. However, in summer the main driver of the surface dust emission is the strong northerly wind ("Shamal") that transport dust from the northern Arabian Peninsula toward south parallel to the Arabian Gulf. The AERONET shortwave Top of Atmosphere Radiative Forcing (TOARF) and at the Bottom of Atmosphere Radiative Forcing (BOARF) have been analyzed and compared with the modeled direct radiative forcing of mineral dust aerosol. The annual modeled TOARF and BOARF are −3.3 and −12 W m⁻², respectively. However, the annual observed TOARF and BOARF are significantly different at −10 and −52 W m⁻², respectively. The analysis of observed and modeled TOARF agrees with previous studies in highlighting the need for more accurate specification of surface albedo over the region. Due to the high surface albedo of the central Arabian Peninsula, mineral dust aerosols tend to warm the atmosphere in summer (June–August).