Abstract:Based on the monthly reanalysis data of MERRA-2 and ERA5, EOF analysis, linear regression and composite analysis are used to analyze the interdecadal variation characteristics of aerosol pollution (Aerosol Optical Depth, AOD) in the Twain-Hu Basin in the middle reaches of the Yangtze River basin during 1980-2020 and the influence of north-south anti-phase mode of meridional wind in East Asia. The results show that the AOD in the Twain-Hu Basin region shows a non-linear trend on the interdecadal scale, with low values in the 1980s and 1990s, a continuous increase in AOD at the beginning of the 21st century, and a decline after 2010. The spatial performance is characterized by a consistent variation across the region, with the high value area mainly located in the middle of the Twain-Hu Basin, with Dongting Lake as the center in a north-south longitudinal distribution. Further analysis of the relationship between the interdecadal variation of AOD and anomalous atmospheric circulation in the Twain-Hu Basin indicates that northerly wind transport is the main meteorological cause of interdecadal variation of AOD in the Twain-Hu Basin under the influence of north-south anti-phase mode of meridional winds in East Asia. On the interdecadal scale, when the intensity and area of Siberian high pressure increase, the East Asian trough shifts westward, and the West Pacific subtropical high shifts southward, the north-south anti-phase mode of the meridional winds in East Asia tend to be in positive phase (i.e., there are anomalous southerly winds in the north of the Yangtze River and anomalous northerly winds in the south of the Yangtze River), the Twain-Hu Basin is located at the bottom of the anomalous cyclonic circulation, and the northerly winds enhance aerosol transport to the Twain-Hu Basin. Moreover, the Twain-Hu basin is in the middle of two anomalous cyclonic circulations, the pressure gradient is small and the wind speed is weak, so that the aerosol input in the Twain-Hu basin is larger than the output, enhancing the interdecadal increase of AOD in the early 21st century.