| Analysis of climatological characteristics and causes of summer droughts in Sichuan-Chongqing region |
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| DOI：10.7606/j.issn.1000-7601.2013.04.042 |
| Key Words: Sichuan-Chongqing region summer drought standard precipitation index atmospheric circulation water vapor transport |
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| Abstract: |
| Using the monthly precipitation data from Climate Research Unit (CRU), University of East Anglia in England and the global monthly mean meteorological reanalysis data at standard isobaric levels from Japan Meteorological Agency (JMA) from 1979 to 2011, the criterion of typical drought years in Sichuan-Chongqing region was determined with the Standardized Precipitation Index (SPI), and the climatological characteristics and possible causes of summer droughts in Sichuan-Chongqing region were analyzed from the aspect of atmospheric circulation. The results show that, during years with typical summer droughts, the surface air temperature is higher and the precipitation is less than n
ormal. The zonal circulation develops in mid-latitude regions of East Asia, and the westerly frontal zone and the cold air mass shift northward during summer droughts. Meanwhile, Sichuan-Chongqing region and most parts of northern China are under the control of mainland belt high pressure. The location of high pressure at 500 hPa field is nearly the same with the center of South Asian high pressure at 100 hPa field. Moreover, the high pressure center at 500 hPa corresponds with the warm center in the temperature filed. This quasi-barotropic structure is the typical circulation feature of a persistent summer drought in Sichuan-Chongqing region. At the same time, the southwesterly flow is obviously weakened from Yunnan-Guizhou Plateau to Sichuan Basin in the low troposphere. In the anomaly wind field, there exist northeasterly flows from Yunnan-Guizhou Plateau to Sichuan Basin, and there is a cyclonic circulation over southern China. The entire-layer southwesterly water vapor transport in typical summer drought years is much weaker than normal in Sichuan-Chongqing region. |
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