Linkage Between AOD And Surface Solar Radiation Variability In Association With East Asian Summer Monsoon Circulation Changes

Based on Aerosol optical depth (AOD) data derived from MODIS sensors on board the Terra satellite and NCEP/NCAR reanalysis from 2000 to 2013,the principal modes that shows the linkage between AOD and near surface downward solar radiation flux (DSRF) in East Asia have been explored with singular value decomposition (SVD) method.That mode is further examined in association with East Asian summer monsoon.Our results demonstrate that:(1) The AOD distribution in East Asia is similar to the DSRF in summer. By using Singular value decomposition method,a positive correlation between AOD and DSRF under the influence of seasonal trends has been found. By calculating the variance contributions,we confirm that seasonal trends are more important than interannual variability in determining the in phase variations of AOD and DSRF.Left time series of the coefficient for the leading mode of the singular vector (SVD1) have been used to conduct correlation analysis.The results suggest that:in June (except 2013),when both AOD and DSRF values are high in east China, the divergence and ascending motion will be stronger than normal from the southeast China to the south of Japan.As a result,summer precipitation will increase.This is due to the fact that location of the west Pacific subtropical high in June is more southern than normal,resulting less rain in northern parts of China eventually.An anomalous warmer area appears in Huabei Region due to the more net surface solar radiation flux.In August,the situation is opposite.All of these results indicate that the seasonal evolution of East Asian summer monsoon plays an important role in regulating the variability of AOD and DSRF.(2) With seasonal trends removed,a negtive correlation between AOD and DSRF has been found by using SVD method, which is also known as "umbrella effect" 20% of the variations of AOD can significantly affect the 10% of the variations of DSRF in East Asia.Left time series of the coefficient for the leading mode of the singular vector (SVD1) have been used to conduct correlation analysis.The results suggest that:when AOD value increases in northeast China and decreases in the coastal areas of South China,the heating differences between north and south continent in East China are increasing, however, that differences between land and sea in the South China are decreasing, which will cause the reduction in SLP differences between land and sea, and finally weakens East Asian summer monsoon. The weakening of summer monsoon results less cloud and rainfall in the area of Huabei region and Dongbei region and South China Sea to Western Pacific region.However, the rainfall is likely to increase over the south of Yangtze river in East China.The temperature in the south of the Yangtze River is lower than normal while it is signicficantly higher in the north of China.(3) Typical strong (weak) AOD events in East Asia are found to co-occur with the weak (strong) East Asia summer monsoon events. The abnormal distributions of strong (weak) AOD are not only influenced by the climatological mean East Asian monsoon, but also a result of abnormal East Asian summer monsoon influcences. The so-named "apparent AOD source" also plays an important role in variations of AOD in East Asia.