Direct and indirect aerosol effects on the climate of the Arabian Peninsula

Atmospheric Aerosols, in addition to the greenhouse gases, represent an important factor in the science of climate change. They scatter and absorb light directly and interact with clouds indirectly leading to changes in radiation budget and the hydrological cycle. The Arabian Peninsula is a major source of aerosols as it contains three deserts producing frequent dust events in addition to being one of the fast growing economies of the world. Here, direct and indirect effects of aerosols on the climate of the Arabian Peninsula are presented using the aerosol - climate model ECHAM5-HAM with GAINS inventory. Six simulations of seven years (2005 -2011) under various possibilities were performed. Aerosols cause directly an annual mean cooling effect over Arabian Peninsula of -0.45 oC, and indirectly an annual warming of 0.54 oC. The annual cycle of precipitation indicates a decrease of -1.76 mm/month due to aerosol direct effect, and an increase of 1.93 mm/month as a result of an indirect effect of aerosols over Arabian Peninsula. Both direct and indirect aerosol effects increase the mean annual cycles of the net radiation flux, cloud cover and evaporation. Aerosol effects vary temporally and spatially over Arabian Peninsula, and its greatest effects on temperature and precipitation occur over Northern region during February and April and over Southern region during August respectively. The direct aerosol effects offset the aerosol indirect effects on temperature and precipitation because of various cloud feedback mechanisms in a warm climate. High clouds tend to be icy and at higher altitudes that yield more effective positive feedback. Aerosol-cloud interaction may increase life time and size of the clouds. Aerosols have distinguished effects on the climate of the Arabian Peninsula. This work may improve aerosol - climate models and furnish the stage for understanding the significance of aerosols and their effects on the climate of arid environment.