Characteristics of Interdecadal Variability in Atmospheric Aerosol Pollution in the Twain-Hu Basin Region in Winter and Spring and Its Association with North–South Antiphase Modes of Meridional Winds in East Asia

Based on MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications) and ERA5 (Fifth major global reanalysis produced by ECMWF) monthly reanalysis data, EOF (Empirical Orthogonal Function) analysis, linear regression, and composite analysis are used to analyze the interdecadal variation characteristics of AOD (aerosol optical depth) in the Twain-Hu Basin in the middle reaches of the Yangtze River basin during 1980–2020 and influence of the north–south antiphase mode of meridional wind in East Asia. The results show that AOD in the Twain-Hu Basin region shows a nonlinear trend on the interdecadal scale, exhibiting low AOD values in the 1980s and 1990s, a continuous increase at the beginning of the 21st century, and a decline after 2010. The spatial performance is characterized by a consistent variation across the study region, and high-value areas are mainly located in the middle of the Twain-Hu Basin, with Dongting Lake being the center in a north–south longitudinal distribution. Further analysis of the relationship between the interdecadal variation in AOD and anomalous atmospheric circulation in the Twain-Hu Basin indicates that northerly wind transportation under the influence of the north–south antiphase mode of meridional winds in East Asia is the main meteorological cause of interdecadal variations in AOD in the Twain-Hu Basin. On the interdecadal scale, when the intensity and area of the Siberian high pressure increase, the East Asian trough shifts westward, and the western Pacific subtropical high shifts southward, the north–south antiphase mode of the meridional winds in East Asia tends to be in a positive phase (i.e., there are anomalous southerly winds to the north of the Yangtze River and anomalous northerly winds to the south of the Yangtze River). Under this positive phase, the Twain-Hu Basin is located at the bottom of anomalous cyclonic circulation; hence, anomalous northerly winds enhance aerosol transport to the Twain-Hu Basin. Moreover, the Twain-Hu Basin is located in the middle of two anomalous cyclonic circulations, resulting in a small pressure gradient and weak wind speed. Therefore, the aerosol input in the Twain-Hu Basin is larger than the output, enhancing the interdecadal increase in AOD in the early 21st century.