The relationship between summer column water vapour and primary climatic variables in eastern China

Stepwise regression analysis was used to investigate the statistical relationships between summer time column water vapour (CWV) and seven primary climatic variables in eastern China. The zonal winds at 850 hPa can either be positive on the CWV or negative, depending on the character of the winds. While the 850 hPa meridional winds generally show a positive effect on the CWV over eastern China, the outgoing longwave radiation shows a stable negative effect. The low-level air temperatures are loosely related to the CWV, in line with the fact that the atmosphere is normally undersaturated and thus the water holding capability of the atmosphere is not the decisive factor. Surprisingly, we found evaporation can even be negatively related to CWV, under the combined result of land surface heating, convective instability, and land surface moistening. To compare the relevant importance of the seven variables and identify the dominant variables of CWV, proportional marginal variance decomposition (PMVD) was further used. The water vapour removing effect of the Westerlies, the drying out indicated either by OLR or by evaporation, and the moistening effect either from evaporation or by monsoon wind show up as primary drivers of the vapour content at various locations in different months. Our research provides an objective and comprehensive understanding of the CWV in eastern China.