The relationship between South Asia High and water vapor variation in the upper troposphere and lower stratosphere in summer

The spatial distribution characteristics of South Asian High (SAH) and water vapor in the upper troposphere and lower stratosphere (UTLS) over the SAH in summer were analyzed based on the ERA-interim reanalysis monthly data from 1979 to 2015. The correlation and causality between the two variables were also discussed. The results are as follows. (1) In the upper troposphere, the area of high water vapor is located on the southeastern side of SAH and tilts northwestward with increasing height until 100 hPa, and the center of water vapor is near the center of SAH. (2) When SAH is stronger (weaker), the water vapor content in the UTLS area of eastern SAH is significantly higher (lower), while the water vapor anomalies in the northwestern SAH are not significant. (3) The reason that water vapor content is higher (lower) in the middle of SAH over the UTLS area when SAH is stronger (weaker) SAH may be because of the suction and transport barrier effects of SAH to water vapor. (4) A stronger (weaker) SAH often corresponds to higher (lower) water vapor content in the UTLS to the southeast of SAH, which is probably associated with the latent heat release induced by deep convective water vapor transport.