Modeling Study On Hemispheric Transport Of Dust Aerosol In Global Major Dust Source Regions

Using global climate model GEM-AQ/EC, CAM3.1and CAM5.1to simulation and a series of modeling studies was conducted:1) Based on the10-year (1995-2004) aerosol simulations of the global aerosol model GEM-AQ/EC, distributions and variations of global dust aerosol sources and sinks;2) A sensitivity study of2-year (2002-2003) CAM3.1modeling was analyzed in the contribution of Trans-Eurasian dust aerosol transport on atmospheric environment in East Asian region;3) By using20-year (1991-2001) simulation from the climate model CAM5.1, impact of Tibetan Plateau topographic changes on dust aerosol in the northern hemisphere. The main results are summarized as follows:1. Global dust emissions are centered over the major desert regions where the North African deserts are estimated with the largest emission contribution to the global dust aerosol up to66.6%. The high dust aerosol depositions are concentrated over the desert sources and their immediately downwind areas. Thereby, the net dust aerosol sinks are largely distributed around the desert regions forming a receptor zone with the net sinks of greater than10t/(km2a) between0°N and60°N from North Africa, Eurasia, west Pacific Ocean, the north Indian Ocean, North America to the Atlantic ocean.In five major deserts of North Africa, Arabian Peninsula, Central Asia, East Asia and Australia, the dust emissions and depositions present the significant seasonal variations, The regional depositions expecting Central Asia experience almost the same seasonal cycle with the emissions; both dust aerosol emissions and depositions oscillate seasonally with the largest amplitudes in East Asia and with the lowest amplitudes in the North Africa. The seasonal dust emissions and depositions peak in summer over Central Asia and the Arabian Peninsula as well as during spring in the other three regions. Over the10years, the global annual emission is averaged with (1500±94) Mt in a slightly rising trend. The inter-annual variability rate of dust emissions in North Africa is lowest (6.3%), up to28.3%in East Asia and highest in Australia (45.0%). The dust aerosol depositions over global land decrease at a rate of around9.9Mt/a, while they increase year to year over the oceans.2. Under the impact of Trans-Eurasian transport on East Asian region, the foreign dust emission sources contribute the dust aerosols to the Tibetan Plateau with the largest rate, to the arid and semi-arid regions in northern China with the lowest rate and to Sothern China and Korean Peninsula, Japan and the adjacent northwest Pacific region with the moderate rate. Autumn and winter are respectively the seasons with the weakest and strongest influences of the foreign dust aerosols on East Asian atmosphere with the contribution rates of about5%in autumn and of about30%in winter over northern China as well as the contribution rates of20-60%in autumn and of60-80%in winter over the Tibetan Plateau. The seasonal patterns of the foreign dust contribution to tropospheric loading and surface concentrations over East Asian region are generally consistent, and the contribution rate to dust loading is10-40%higher than that to surface dust concentrations. The influences of foreign dust aerosol controlled by the trans-Eurasian dust aerosol transport are vertically concentrated at2-6km in the free troposphere with the larger contribution rate at the higher elevation. The Tibetan Plateau with the62-81%contribution rate of foreign dust aerosols to the tropospheric atmosphere on the annual and regional averages is the region with the largest impact of foreign dust aerosols in the East Asian region.3. Tibetan Plateau uplift makes the dust emissions of the major desert regions present obvious variations in the northern hemisphere, in addition to the Arabian Peninsula and the Middle East dust emissions are reduced (17Mt), North Africa and East Asia are increased39Mt and38Mt respectively, and the maximum variation and the largest dust emissions occurred season is consistent in the two regions. The existence of the Tibetan Plateau makes the surface dust concentrations present the significant seasonal variations in the major desert, and the most of North Africa the surface dust concentrations is increased only the northern of North Africa in summer is reduced, in northern China surface dust concentration increased and the most obvious in summer, the Tibetan Plateau surface dust concentration reduced in spring the most significant; Arabian Peninsula surface dust concentration significantly increased only in summer, while the other three seasons are reduced. The impact of the Tibetan Plateau uplifting on distribution of dust loading in the northern hemisphere is not great, high value still is centered over the major deserts, but the eastern North Africa and the Arabian Peninsula regions over the summer easterlies enhanced, while the westerlies weakened in winter.