The Temperature Anomaly Averaged In The Troposphere Of The Tibetan Plateau And Its Effects On Subtropical Westerly Jet Center Over The Tibetan Plateau In Spring

With the NCEP/NCEP reanalyzed data, seasonal characters in the mid-upper troposphere over Tibetan Plateau can be concluded. By integrating over the temperature of whole layer in the mid-upper troposphere and then calculating the zonal departure, an index describing the thermal anomaly over Tibetan Plateau will be introduced, called TDI (Tibetan middle-high level temperature zonal deviation index), moreover, the changes of the index are also showed. According to the space distributions of Tibetan Plateau subtropical westerly jet, the ECMWP (ERA-interim) reanalyzed data is used to define two indices which represent the location and intensity of the jet respectively. Lastly, the influence of TDI in spring on the jet is studied. Major conclusions:(1) The inter-monthly change of TDI showed a single maximum. The thermal effect increases gradually in April and reaches the maximum in July, then decreases rapidly after September. The index is high obviously in spring (from April to June) and in summer (from July to September). Concerned about climatic and interannual changes, comparing with other traditional indexes, the trend of index is same as others generally, which is verifying the dependability of this index.(2) The interannual change of TDI is obvious. Results of wavelet analysis show that the annual cycles of different months vary. There are evident variations of the index among different months and seasons.(3) From April to June, the center of subtropical westerly jet over the plateau moves northerly. From winter to summer, the jet moves to the north, and the speed of wind in the center becomes small. From summer to winter, the change is opposite with the previous. Using the axis method and the zone leveling method to define the indexes describing position and intensity of the jet, evident interannual fluctuation exists in the two indexes. At the same time, the indexes are largely consistent with the cycles of TDI at the same term in different months.(4) TDI in spring has closely connection with the circulation over the plateau, when the TDI is large(small), the potential height over the plateau is high(low), and the airflow is abnormal by west(east) from low-upper to high-upper over the plateau, then the airflow in south is abnormal by east(west), at the same time, there is a obvious and abnormal anticyclone (cyclone) circulation. From April to June, the areas where potential height is positive and the boundary between abnormal easterly and westerly wind move to the north obviously.(5) TDI in spring has close relations with the indexes describing position and intensity of the jet in the same term. When the TDI is large (small), the position of the westerly jet is northerly (southerly), and the intensity of westerly jet over the plateau and its north is strong (weak).