Study On The Atmospheric Dust Aerosols’ Changes Over The Major Deserts Of The World

Dust aerosols with their cooling effect on earth surface are regarded as an Earth refrigerant contrary to the warming effect of carbon dioxide. Dust aerosls link land, sea and air in the geochemical processes, which is a key chain on global substance cycle and climate change. Currently, it is generally believed that dust aerosols are injected in the atmosphere during dust storms. Whereas, observations evidences, especially the27-year records of aerosol index(AI) of1979-2009, revealed that only dust storms can not explain the diurnal and monthly variation of observed dust aerosols. The AI-distribution over the major deserts of the world presented the high AI during the non-dust storm periods. This implies that the dust emission mechanisms except dust storms could lift dust aerosols into the atmosphere. These dust emission mechanisms include dust devils, convective plumes, and turbulent convection. It is difficult to observe dust devils and convective plumes with no available observation data for the current studies. However, the dust devils and convective plumes are driven by solar radiation. Therefore, the aerosol contributions of dust devils and convective plumes could implicitly be estimated in proportion to solar radiation. The analyses on the impacts of solar radiation、dust storm frequency and precipitation on the AI over the major deserts could interpret the underestimation of simulated dust emission fluxes and is also helpful in understanding the dust aerosol source, sedimentation and their environmental effects.We analyze the AI-varaitions over five major desert regions including Sahara、the Arabian Peninsula、South Asia、China and Australia based on27year observation data. We also discuss the dust emissions from the desert regions in association with solar radiation、dust storm frequency and precipitation. The study results are concluded as follows:(1) The annual AI values of almost over0.7in the five major desert regions and higher were higher than in other regions. During dust storm periods, a great quantity of dust aerosols emitted into the atmosphere with the significantly increasing AI. Although dust storms have an obvious influence on the tempo-spatial AI-distribution, the very high AI during non-dust storm periods was also observed over the global deserts contributed by dust devils and convective plumes.(2) Solar radiation and AI over the major deserts in both Northern and Southern Hemisphere showed the significant positive correlations in the diurnal and monthly variation. AI over desert regions in the Northern Hemisphere peaked around June, when the low AI of Australian desert regions in the Southern Hemisphere was accompanied with the solar radiation, which further confirmed the positive correlation between AI and solar radiation. It is suggested that solar radiation is one of the most important factors controlling dust aerosols over the desert regions. Dust devils and convective plumes triggered by solar radiation had a large dust contribution to the aerosols in the atmosphere.(3) High AI was resulted from the dust aerosols emitted by dust storm, dust devils and convective plumes. Nevertheless, precipitation could scavenge dust aerosols in the atmosphere reducing AI over the desert regions. Precipitation and AI had the negative correlations.(4) Based on regression statistics, the trend in AI could be well built by solar radiation, dust storm frequency and precipitation.