Characteristics of Water Vapor Content in Southwest China and Its Association with the South Asia High in Summer

Based on ERA-interim high resolution data by ECMWF from 1979 to 2014, in terms of EOF decomposition, wavelet transform, anomaly composite and correlation analysis, spatial and temporal variations of atmospheric water vapor content in Southwest China and its relationship with the South Asia High in summer are discussed. Results indicate that the spatial distribution morphology of summer atmospheric water vapor content in Southwest basically has the same anomaly in whole type, north-south oscillation type and east-west oscillation type, and the explained variance of EOF1 is much higher than those of EOF2 and EOF3, which means the same anomaly in whole type (EOF1) can reflect the main distribution characteristic of water vapor content in Southwest China in summer. The summer atmospheric water vapor content in Southwest China shows obvious inter-annual variation characteristics, and there is obviously corresponding relationship between summer atmospheric water vapor content in Southwest China and the South Asia High. More (less) water vapor content is accompanied with stronger (weaker) South Asia High. Furthermore, there are significant positive correlations between the water vapor content in Southwest China and the South Asia High intensity index, the area index and the eastward index, which reach 0.64, 0.62 and 0.59, respectively. In addition, when the South Asia High strengthens, the subtropical high over the West Pacific extends to west, and the southwest airflow of the lower troposphere is enhanced, which is favorable for the water vapor transport to the south of China from the ocean. Meanwhile, the South Asia High enhances the upward motion in Southwest China, causing more water vapor content. On one hand, the westward extension and the strengthening of subtropical high guides the Western Pacific water vapor transport to the southwest of China; on the other hand, due to blocking effects of the subtropical high, the water vapor which transported from the South China Sea leads to increased atmospheric water vapor content in Southwest China. When the South Asia high is weakened, the situation is the opposite.