Impact Of Tibetan Plateau On Eurasian Atmospheric Circulation In Late Spring And Early Summer

The NCEP reanalysis data from 1960 to 2007 were used to calculate the latent heat, the radioactive cooling and the atmospheric heat source over the Tibetan Plateau (TP). The normalized indexes for Plateau Ts-Ta (differences between ground and air temperature),sensible heat(SH), latent heat(LH), the radioactive cooling and the atmospheric heat source were defined within TP region. After analyzing the relationship between Plateau Ts-Ta and the various components of Plateau atmospheric heat source, we found that the increase of the Plateau Ts-Ta was associated closely with increase of the plateau SH and the plateau LH, but the decrease of the radioactive cooling in May and June. Its increase roughly implied the increase for atmospheric quantity of heat in May and June.The impact of Plateau Ts-Ta and Plateau atmospheric heating on atmospheric circulation in Eurasia was analyzed by using a linear regression method, which indicated that When the Plateau Ts-Ta was large, several wave train-like height anomaly centers appeared around Ural Mountains, the west of Siberia, Okhotsk Sea, the east of Japan and subtropical area near the international date line respectively. The Plateau atmosphere heat content was associated with a similar pattern except for the centers drifting. Similar results were also found in June. Note that when Plateau Ts-Ta increases, or the Plateau atmosphere heat content increase in May and June, the positive height anomaly around the Okhotsk Sea and negative height anomaly around the sea area east of Japan tend to occur. This coincides with the eastern of positive phase of the OKJ propagation. In other words, in late spring and early summer, Plateau Ts-Ta or the Plateau atmosphere heat source enlargement were in favor of the development of the OKJ wave eastern section.In order to confirm the analysis results, this study performed a suite of sensitivity experiments with NCAR CAM3.1 model. The simulating results were consistent with the diagnosis. The effects of the Tibetan Plateau topography on Eurasian atmospheric circulation were studied too. The experiments with and without TP (called CTL Experiment and NTP Experiment hereafter) were performed respectively by using an atmospheric general circulation model (NCAR CAM 3.1). The results suggested: Rossby wave train-like height centers originated from Mongolia region, via Okhotsk Sea, Aleutian Islands to the west coast of North America in May. Because the middle latitude westerly jet moves northward, weakens and the Plateau diabetic heating is enhanced from May to June, the wave train-like height centers slightly changed their positions and weakened in June. Additionally the wavelike around Okhotsk Sea and the East of Japan suppressed the positive phase of East of OKJ wave train, whose effect was strong in May and weak in June.