The impact of diabatic heating over the Tibetan plateau upon Northeastern Asia arid region
T. Sato (1), F. Kimura (2)
(1) University of Tsukuba
(2) University of Tsukuba, Frontier Research Center for Global Change
Formation mechanism of arid climate over northern China is investigated by a series of Regional Climate Model (RCM) experiments. On that region summertime precipitation is strongly reduced by a prevailing regional scale subsidence. Sensitivity experiment without condensation process (NoC) is conducted in order to clarify the physical mechanism for the generation of the subsidence. Simulated vertical velocity shows the descent at middle troposphere over arid region. At the same time, ascending motion appears immediate above the Tibetan plateau, because the planetary boundary layer acts as an elevated heat source over the plateau. However, only gentle vertical motion is left in the case when diabatic processes is turned off in the model. That implies mechanically forced subsidence by the terrain, such as mountain wave, is not enough to cause the subsidence. To the contrary, thermal effect of the plateau is fairly larger since the subsidence over arid region is enhanced when diabatic heating is artificially given only over the plateau. Northward propagation of the stationary Rossby wave is inferred to cause the robust subsidence over the arid region in northern China. The stationary Rossby wave tends to propagate northward because subtropical westerly jet is being situated north of the plateau in boreal summer. Therefore, the stationary descending motion prevails over northeastern Asia, which consequently reduces the precipitation around arid region. Diabatic heating over tropical region does not affect directly over the desert since the position of subtropical westerly is not favorable for northward propagation of Rossby wave. We also confirmed that the stationary Rossby wave is likely to propagate not only northward but also southward of the plateau when zonal mean of January is assumed as a boundary condition. Spatial relationship between the plateau and the westerly jet undergoes transition period from spring to summer. The relationship could widely affect the seasonal evolution among Asian region since the spatial distribution of the subsidence will be changed simultaneously around the plateau.
Submittal Information
Name :
Date :
Tomonori Sato
27-Jul-04-12:31:59
Organization :
Theme :
University of Tsukuba
Theme 4
Address :
Presentation :
Life and environmental Sciences, University of Tsukuba, Tsukuba, 305-8572