A New Index for Surface Sensible Heat Flux over the Tibetan Plateau and Its Possible Impacts on the Rainfall in South China

The intensity of surface sensible heat flux (SH) over the Tibetan Plateau is one of the most significant prior signals for precipitation anomalies in China. However, it's always a challenge to establish an index to describe the strength of SH due to the lack of corresponding observations and the complex topography. Based on the monthly surface sensible heat flux over the Tibetan Plateau which is calculated from observations including air temperature, land surface temperature, near surface wind speed and pressure in 70 meteorological stations provided by China Meteorological Administration (CMA) and normalized difference vegetation index (NDVI) observed by National Oceanic and Atmospheric Administration (NOAA) remote sensing satellites and the season reliant EOF method (SEOF), 4 representative stations are chosen, a new sensible heat index (I_SH) is defined, and then the monthly I_SH from 1982 to 2012 is calculated. By comparing with the average sensible heat in 70 stations which represents the regional averaged sensible heat condition in the mid-eastern Tibetan Plateau, surface heating strength index (B-H) and two indices of Xizang Plateau from National Climate Center, it's concluded that the inter-annual variabilities of I_SH can represent the surface sensible heat in the middle and eastern region of the Tibetan Plateau, and this index has better relationship with two indices of Xizang Plateau than B-H, especially in winter, which mean I_SH reflects geopotential height anomalies respond to surface heat better. Then the relationship between I_SH in spring and the summer rainfall (total precipitation in June and July) in South China from 1982 to 2012 is discussed based on the monthly rainfall data in 92 meteorological stations provided by CMA and the monthly NCEP/NCAR reanalysis data. Results show that I_SH in spring bears significant negative correlations with summer rainfall in South China. The larger index in spring indicates higher geopotential height in mid-low latitudes and lower in high latitudes during next several months, and the positive anomalies in mid-low latitudes transfer from middle troposphere to upper and maintain in 200 hPa, which may lead to the westward extension of subtropical high in 500 hPa, the South Asian high in 200 hPa and westerly wind around 40°N enhancing, whereafter, it may result in the downdraft and southerly wind enhancing, but water vapor convergence subside in South China, moisture can be transported to northern region through South China. And finally, it will cause the reduction of precipitation in South China during the summertime. In addition, negative correlations will become even more significant after removing the influence of sea surface temperature (SST) in regions of Niño3.4, which indicates there may be more complex coupled influence derived from the Tibetan Plateau heating and SST anomalies in Niño regions.