Abstract
Abstract. The Tibetan Plateau (TP), referred to as the "roof of the world", is also known as the "world water tower" because it contains a large amount of water resources and ceaselessly transports these waters to its surrounding areas. However, it is not clear how these waters are being supplied and replenished. In particular, how plausible hydrological cycles can be realized between tropical oceans and the TP. In order to explore the mechanism sustaining the atmospheric "water tower" over the TP, the relationship of a "heat source column" over the plateau and moist flows in the Asian summer monsoon circulation is investigated. Here we show that the plateau's thermal structure leads to dynamic processes with an integration of two couplings of lower convergence zones and upper divergences, respectively, over the plateau's southern slopes and main platform, which relay moist air in two ladders up to the plateau. Similarly to the CISK (conditional instability of the second kind) mechanism of tropical cyclones, the elevated warm–moist air, in turn, forces convective weather systems, hence building a water cycle over the plateau. An integration of mechanical and thermal TP forcing is revealed in relation to the Asian summer monsoon circulation knitting a close tie of vapor transport from tropical oceans to the atmospheric "water tower" over the TP.
Highlights
It has long been known that the Tibetan Plateau (TP) as the third pole and “the world water tower” (Xu et al, 2008; Qiu, 2008) plays an important and special role in global climate and energy–water cycle
In this study focusing on the climate mean in boreal summer, we investigate the mechanism in which a portion of moist air reaches over the TP to maintain the atmospheric “water tower”, as shown with high vapor contents over the TP in the lower panel of Fig. 1
Occurrences of convective clouds over the TP are observed with 2.5 times of the regional mean over the other areas of China (Xu et al, 2002), and the TP region is regarded as a high frequency center of cumulonimbus or mesoscale convective systems (MCSs) in China (Sugimoto and Ueno, 2012), which is confirmed by the mean distribution of convective clouds over the TP in the plateau low vortex region
Summary
It has long been known that the Tibetan Plateau (TP) as the third pole and “the world water tower” (Xu et al, 2008; Qiu, 2008) plays an important and special role in global climate and energy–water cycle. Xu et al (2008) identified the role of TP as the world water tower, and elucidated how a hydrological cycle is completed over the plateau and its surrounding areas, and how atmosphere is able to supplement and reinforce the water that has been continuously transported away from the TP These studies certainly indicate that despite the fact that a large amount of water vapor is deflected to southeast China, there must be an appreciable amount of moist flows that are able to climb over the TP, supplying and depositing necessary amounts of water onto the TP, to make up the depleting surface flows. The two “water connected pumps” will mutually support each other in such a way that they ladder and relay the moist air over the elevated plateau
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