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摘要
We present a comprehensive analysis of the interannual variability and trend of dust aerosol in Central Asia (37 degrees-55 degrees N, 50 degrees-80 degrees E) from 2000 to 2014, based on a set of dust emission simulations using the WRF-Chem-DuMo modeling system, observations of dust frequency derived from surface station synoptic weather records, and dust optical depth (DOD) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) aerosol optical depth (AOD) products. Model simulations reveal that the soil grain size distribution has little impact on the interannual variability of dust fluxes but strongly affects their magnitude. The two physically based dust schemes based on Marticorena and Bergametti (1995) (MB) and Shao et al. (1996) (Shao) produce large differences in the dust flux magnitude and spatiotemporal distributions, largely due to different sensitivities of the threshold friction velocity to vegetation-induced surface roughness. By using a fixed threshold velocity, the dust scheme of Tegen and Fung (1995) (TF) relies on the dynamic dust source function to capture the dust variability associated with vegetation changes. Through a correlation analysis, the simulated dust fluxes show good consistency with the observed dust frequency, whereas only the Shao and TF dust fluxes are consistent with the MODIS Collection 5.1 and SeaWiFS DOD. The dust fluxes, dust frequency, and DOD (except MODIS Collection 6) are highly correlated with the frequency of strong surface winds but show different sensitivities to drought and soil erodibility factors (i.e., precipitation, soil moisture, and vegetation) which are influenced by El Nino-Southern Oscillation (ENSO). In general, La Nina years are associated with reduced precipitation, drier soils, less vegetation, and, consequently, more severe drought and enhanced dust activity in Central Asia. The averaged dust flux of the MB and Shao experiments shows a significant negative trend of 2.00 +/- 0.59 x 10(-3) gm(-2) yr(-1) from 2000 to 2014, which is consistent with the trends in the TF dust flux (-1.74 +/- 0.34 x 10(-3) gm(-2) yr(-1)), dust frequency (-0.63 +/- 2.1x10(-3) yr(-1)), and SeaWiFS AOD (-3.3 +/- 1.3 x 10(-3) AOD yr(-1)), as well as the decreasing tendency in the MODIS AOD after the ENSO effect is removed. The negative dust trend is driven by a decline in the surface winds, which is likely due to changes in large-scale atmospheric circulation rather than the local effect of vegetation-induced surface roughness.
- 出版日期2015-12-16
