Features of the Extremely Severe Drought in the East of Southwest China and Anomalies of Atmospheric Circulation in Summer 2006 |
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Authors: | Yonghua Li Haiming Xu De Liu |
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Affiliation: | Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science & Technology, Nanjing 210044
Chongqing Institute of Meteorological Sciences, Chongqing 401147;Key Laboratory of Meteorological Disaster of Ministry of Education, Nanjing University of Information Science & Technology, Nanjing 210044;Chongqing Municipal Meteorological Bureau, Chongqing 401147 |
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Abstract: | The spatial-temporal features of the extremely severe drought and the anomalous atmospheric circulation in summer 2006 are
analyzed based on the NCEP/NCAR reanalysis data, the characteristic circulation indices given by the National Climate Center
of China, and the daily precipitation data of 20 stations in the east of Southwest China (ESC) from 1959 to 2006. The results
show that the rainless period started from early June and ended in early September 2006 with a total of more than 80 days,
and the rainfall was especially scarce from around 25 July to 5 September 2006. Precipitation for each month was less than
normal, and analysis of the precipitation indices shows that the summer precipitation in 2006 was the least since 1959. The
extremely severe drought in the ESC in summer 2006 was closely related to the persistent anomalies of the atmospheric circulation
in the same period, i.e., anomalies of mid-high latitude atmospheric circulation, western Pacific subtropical high (WPSH),
westerlies, South Asian high, lower-level flow, water vapor transport, vertical motion, and so on. Droughts usually occur
when the WPSH lies anomalously northward and westward, or anomalously weak and eastward. The extreme drought in summer 2006
was caused by the former. When the WPSH turned stronger and shifted to the north and west of its normal position, and the
South Asian high was also strong and lay eastward, downdrafts prevailed over the ESC and suppressed the water vapor transfer
toward this area. At the same time, the disposition of the westerlies and the mid-high latitude circulation disfavored the
southward invasion of cold air, which jointly resulted in the extremely severe drought in the ESC in summer 2006. The weak
heating over the Tibetan Plateau and vigorous convective activities over the Philippine area were likely responsible for the
strong WPSH and its northwestward shift in summer 2006. |
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Keywords: | the east of Southwest China extremely severe drought anomalous atmospheric circulation |
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