Premonitory of water vapor transport in the upstream key region over the Tibetan Plateau during the 2008 snowstorm disaster in South China.

Using NCEP/NCAR reanalysis data, observational precipitation in China and precipitable water vapor (PWV) data from GPS stations in the Tibetan Plateau and its vicinity, thermal and dynamic features and the variation and transportation of water vapor in the 2008 heavy snowstorm disaster in South China are analyzed by statistical diagnosis. Results show that during the snowstorm disaster, under the large scale background with “trough in south and ridge in north”, strong cold air caused by prevailing northerly wind in northern Asia wedged into low level atmosphere over Southeast China and formed a “clod cushion”. At the same time, warm-wet air was also transported to Southeast China by southerly wind. The vertical shear of winds from cold to warm airflows produced strong upward motion and then, the warm-wet air over the cold air wedge was driven to rise. Finally, the structure of “warm cover” and “cold cushion”, as well as corresponding vertical circulation over the converging frontal zone came into being. The water vapor supply of the 2008 snowstorm in South China mainly came from the South China Sea and the Indian Ocean. These two branches of water vapor transport channels merged in the Indo China Peninsula and Southwest China, and then formed a strong southwest water vapor transport stream passing through Yunnan Province and the nearby. This was the important water vapor transport channel of the snowstorm disaster in the Yangtze River Valley in 2008. From our study, it is found that the water vapor observation from the GPS network serves as an important forecasting tool and provides initial information needed for the assimilation in numerical model simulations of the rainfalls in the middle and lower reaches of the Yangtze River. The water vapor convergence in Yunnan Province and its surrounding areas indicated occurrence of later precipitation in the downstream regions, i.e., the variation of PWV in the upstream key region of water vapor transport can be used as a premonitory signal of the snowstorm disaster. It can also be seen that Yunnan Province is the most important key region for the southwest water vapor transport.