Construction Of A New Heating Index Based On The Zonal Deviation Temperature Over The Tibetan Plateau

Adopting the ERA-Interim reanalysis datasets in recent 36 years (from 1979 to 2014),including monthly mean temperature, distributions of zonal deviation temperature in the mid-upper troposphere (500-150 hPa) are analyzed. According to the distributions,a new index by averaging in the zonal temperature deviation over the Tibetan Plateau from 500-150 hPa is introduced to measure the thermal forcing of the plateau. The index is called Plateau Heating Index (short for PHI). And seasonal variations of the index and its relationships with the circulation, including with the precipitation in summer in the East China are also showed. Then the results are as follows.The core with warmest zonal deviation temperature in the mid-upper troposphere changes monthly. The main regular pattern shows that the core with warmest air rapidly moves from Western Pacific to the plateau in spring, then moves to Western Pacific rapidly in autumn again. And, monthly changes of PHI show a single maximum, which appears in July. And except from November to next February, the value of the PHI is always positive.Additionally,using monthly mean zonal winds and the potential height from ERA-Interim reanalysis datasets in recent 36 years (from 1979 to 2014), some patterns between the PHI and circulation in East Asia are found and they are also interesting. For the zonal winds in East Asia, the boundary of the positive and negative correlation coefficients between the zonal winds with PHI is about located on a line with the 30°N in latitude. For specific performance, the correlation coefficients are positive in the north of the border and negative in the south of the border. Refer to the thermal wind relationship, the characteristic means that the westerly winds in the north of the plateau strengthen and the westerly winds in the south of the plateau weaken when PHI is strong, and vice versa. That is to say that the strong PHI benefits the strength of the subtropical westerly jets. Besides, for the potential height, correlation coefficients between potential height in 200 hPa over the Tibetan Plateau and PHI are always positive over the plateau, which indicates the heating in the troposphere in favorable to the increase of potential height over the plateau. For further interpretation, the abnormality of PHI in summer can characterize the change of the South Asia High. When the value of PHI in summer is high (low), the anomaly of potential height over the plateau is positive (negative),and the South Asia High is strong (weak).In summer, the precipitation in the middle and lower Yangtze River is more than the normal and in the north China when PHI is high. By influencing the subtropical high and meridional circulation, the heating of the plateau causes the anomalies of the precipitation in the East China.