An improved south Asian summer monsoon index with Monte Carlo test
Shi Neng (施能)ab, Gu Jun-Qiang (顾骏强)c, Yi Yan-Ming (易燕明)b, Lin Zhen-Min (林振敏)d
a Nanjing University of Information Science and Technology, Nanjing 210044, China; b Guangzhou Institute of Tropical and Oceanic Meteorology, Guangzhou 510080, China; c Zhejiang Meteorological Science Research Institute, Hangzhou 310017, China; d Meteorological Bureau of Guangxi Province, Nanning 530022, China
Abstract The Indian monsoon intensity index suggested by Webster and Yang (WY index) is optimized and improved in this paper. At first, the area (40$^{\circ}$E--110$^{\circ}$E, 0$^{\circ}$--20$^{\circ}$N) for calculating the zonal wind-shear between 850hPa and 200hPa in the WY index is optimized and adjusted according to the significance test of differences of wind fields. Then the regionally averaged zonal wind is computed over the optimized area. Finally, the optimal linear combination of the zonal winds at the two levels is performed using the regression method, thus defining a new broad-scale circulation index for the interannual variability of the south Asian summer monsoon, i.e. the improved south Asian summer monsoon index. Results indicate that the improved south Asian summer monsoon index has two advantages: its correlation with the All Indian Summer Monsoon Rainfall index is higher than that of WY index, and its computational domain of circulation is also larger than that of WY index. The computational results based on the 1948--98 NCAR/NCEP wind data indicate that the correlation of the improved SASM index with the All Indian Summer Monsoon Rainfall index is higher than that of WY index by 0.27.
Received: 14 October 2004
Revised: 10 November 2004
Accepted manuscript online:
Fund: Project supported by the National Natural Science Foundation of China (Grant Nos 40275031 and 40275028).
Cite this article:
Shi Neng (施能), Gu Jun-Qiang (顾骏强), Yi Yan-Ming (易燕明), Lin Zhen-Min (林振敏) An improved south Asian summer monsoon index with Monte Carlo test 2005 Chinese Physics 14 844
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