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Mechanism of the influence of the Tibetan-Iranian Plateaus on the circulation and climate in summer

April 27, 2017

The highest and largest plateau in the Northern Hemisphere, the Tibetan Plateau (TP), is in the subtropical region of Asia. The air quality above the TP is only 60% of the sea level. In addition, because the radiation over the plateau, especially in the boundary layer is significantly different from those in the low altitude region, the thermal process over the TP has obvious particularity. Through its special thermodynamic and dynamic effects, the TP and its adjacent Iran Plateau (IP) have significant impacts on the circulation and climate over the plateaus as well as the adjacent region and the globe. However, the interaction and feedback among the heat source of the TP and IP and circulation is not clear nowadays.

Recent research papers have made new progress in this issue. Professors Wu Guoxiong and Liu Yimin and their students who come from the Institute of Atmospheric Physics, Chinese Academy of Sciences, conducted the study. With theoretical diagnostic analysis and simulations by regional model, the researchers have revealed the physical process of interaction and feedback between the two types of summertime heating, the surface sensible heating and condensation heating over TP and the surface sensible heating over Tibetan-Iranian Plateaus. They also discovered how this interaction influences the vertical thermodynamic structure near the tropopause over Asia and the atmospheric circulation in the globe.

The maintenance of a steady state in the atmosphere is only possible by obtaining external energies, particularly through the transfer of surface sensible heating, evaporation-condensation heating. This study showed that the TP surface sensible heating can generate convective precipitation over the southern and eastern TP, whereas the precipitation over the TP can reduce the in situ surface sensible heating. This indicates the existence of a feedback or interaction process between the two types of diabatic heating over the TP. Furthermore they documented that the surface sensible heating over the two plateaus not only have mutual influences but also feedback to each other. The IP surface sensible heating can reduce the surface sensible heating and increase the condensation heating over the TP, whereas the TP surface sensible heating can increase IP sensible heating, thereby reaching quasi-equilibrium among the surface sensible heating and condensation heating over the TP, the IP surface sensible heating and the atmosphere vertical motion. Therefore, a so-called Tibetan-Iranian Plateau coupling system (TIPS) is constructed, which influences atmosphere circulation (Figure).

"The interaction between surface sensible heating and latent heating over the TP plays a leading role in the TIPS" said Prof. Wu. The surface sensible heating of the IP and TP influences on other regions not only have superimposed effects but also mutually offset, the combined influence over TP and IP represents the major contribution to the convergence of water vapor transport in the Asian subtropical monsoon region. In addition, the heating of TIPS increases the upper tropospheric temperature maximum and lifts the tropopause, cooling the lower stratosphere. Combined with large-scale thermal forcing of the Eurasian continent, the TIPS produce a strong anticyclonic circulation and the South Asian High that warms the upper troposphere and cools the lower stratosphere, thereby affecting regional and global weather and climate.

The results improved the understanding on the unique feature of the climate dynamics of the TP. It will also help the regional weather and climate prediction.
The study was funded by the Key Program and integration Program of the Major Research Plan of the National Natural Science Foundation of China (No. 91437219 and .91637312)

See the articles:

Liu Y M, Wang Z Q, Zhuo H F, Wu G X. 2017.Two types of summertime heating over Asian large-scale orography and excitation of potential-vorticity forcing II.Sensible heating over Tibetan-Iranian Plateau. Science China Earth Sciences, 60(4): 733-744

Wu G X, Zhuo H F, Wang Z Q, Liu Y M. 2016.Two types of summertime heating over the Asian large-scale orography and excitation of potential-vorticity forcing I. Over Tibetan Plateau. Science China Earth Sciences, 59 (10): 1996-2008

The articles were published online and

Science China Press

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