Summary

This talk gives an overview of the major dust related research conducted recently in the group at KAUST that comprises calculating of dust climatological distributions, direct radiative forcing (DRF), and its continental-scale and regional climate effects.

Aerosol optical depth (AOD) retrievals from the MODIS and SEVIRI instruments are first evaluated via comparison with ship-based observations. Calculations of the DRF along the ship cruises also show good agreement with co-located estimates from the MODIS and GERB instruments. A monthly climatology of AOD over the Red Sea created using MODIS and SEVIRI retrievals show enhanced aerosol loading and a distinct north to south gradient across the basin in the summer relative to the winter months.

To improve the simulations of dust mass balance and dust radiative impact over the Middle East (ME) we have conducted multiyear measurements of dust deposition using passive dust samplers, aerosol optical depth using CIMEL Robotic and hand-held sun-photometers, and aerosol vertical distribution using a micro-pulse lidar. These observations are employed to constrain the WRF-Chem simulations and to test the recent MERRA2 reanalysis.

The aerosol DRF indicates that although long-wave effects can reach 10s of W m-2, shortwave cooling typically dominates the net radiative effect. In summer DRF reaches 60 W m-2 at the surface in the southern part of the Red Sea.

To study the dust effect on the regional ME climate and Red Sea we employ the Regional Ocean Modeling system (ROMS) fully coupled with the Weather Research and Forecasting (WRF) model. The WRF was modified to interactively account for the aerosol radiative effects.

To study the dust large-scale impacts in the larger ME and North Africa (MENA) region we used a high-resolution global atmospheric model with the grid spacing of 25 km. We found that dust surface cooling and heating of the atmospheric column cause a northward shift of the rain belt over Africa in summer increasing precipitation in Sahel.

The Red Sea and MENA climate appears to be sensitive to dust forcing that has to be properly accounted for in the regional and global climate projections.