Causative Analysis of Continuous Drought in Southwest China from Autumn 2009 to Spring 2010
Based on the 1951—2010 daily Compound Index (CI) and atmospheric circulation monitoring index provided by National Climate Center, the daily precipitation data of the 335 stations in the Southwest China, the daily NCEP/NCAR reanalysis data and the daily OLR data of NOAA, the distribution of the drought patterns in the Southwest China was analyzed by using the REOF method, and the characteristics of atmospheric circulation anomalies such as western Pacific subtropical high (WPSH), Indian Burma trough, convection activities, water vapor transportation, and vertical motion of the continued drought from autumn 2009 to spring 2010 in the Southwest China were revealed according to the composite analysis and correlation analysis methods. It was found that the extreme drought occurred in the medium strength and central pattern El Ni〖AKn~D〗o background, instead of statistical typical La Ni〖AKn~D〗a background. The results indicated that influenced by the central type El Ni〖AKn~D〗o, the anti Walker circulation caused the significantly abnormal sinking movement around 120°E in the equator and a strong abnormal anti cyclone in the South China Sea and the surrounding areas of Southeast Asia. At the same time, the Southwest China was affected by the abnormal northwest air stream. By both influences, an obvious airflow divergence area occurred in the lower troposphere and its persistence was the key cause for the extreme drought.