South Asian Summer Monsoon Index (SASMI)

The South Asian summer monsoon index (SASMI) is defined as an area-averaged seasonally (JJAS) dynamical normalized seasonality (DNS) at 850 hPa within the South Asian domain (5°-22.5°N, 35°-97.5°E) (Li and Zeng, 2002, 2003, 2005).

The SASM contains two independent components, Southwest Asian Summer Monsoon (SWASM) over the Southwest Asia (2.5°-20°N, 35°-70°E) and Southeast Asian Summer Monsoon (SEASM) over the Southeast Asia (2.5°-20°N, 70°-110°E), with quite different dynamical influences on the monsoon rainfall over the South Asia (Wang and Fan, 1999; Li and Zeng, 2002). The summer monsoon indices over the Southwest and Southeast Asia are abbreviated to SWASMI and SEASMI, respectively.

                                                                       The South Asian Summer Monsoon Index (SASMI)

 The normalized time series of SASMI (a), SASMI1 (b) and SASMI2 (c) for the period of 1948-2023.

The summer here is JJAS. The thick solid lines indicate 9-year Gaussian-type filtered values.

Correlation maps between the seasonal (June-September) rainfall over the South Asian and (a) SASMI, (b) SASMI1, and (c) SASMI2 for the period of 1979-97. The shaded areas indicate significant at the 95% confidence level.

 Correlation between precipitation and the SASMI (shading) and regression of 850-mb winds against the monsoon index (vectors) for June, July, August and September from 1979 to 2006, respectively. The shaded areas and vectors indicate significant at the 95% confidence level.

 Correlation between precipitation and the SASM1I (shading) and regression of 850-mb winds against the monsoon index (vectors) for June, July, August and September from 1979 to 2006, respectively. The shaded areas and vectors indicate significant at the 95% confidence level.

 Correlation between precipitation and the SASM2I (shading) and regression of 850-mb winds against the monsoon index (vectors) for June, July, August and September from 1979 to 2006, respectively. The shaded areas and vectors indicate significant at the 95% confidence level.

Related References

• Li, J. P., J. Feng, and Y. Li, 2011: A possible cause of decreasing summer rainfall in northeast Australia. Int. J. Climatol., 31, doi: 10.1002/joc.2328. PDF
• Li, J. P., Z. W. Wu, Z. H. Jiang, and J. H. He, 2010: Can global warming strengthen the East Asian summer monsoon?. J. Climate, 23, 6696-6705. PDF
• Feng, J., J. P. Li, and Y. Li, 2010: A monsoon-like Southwest Australian circulation and its relation with rainfall in Southwest Western Australia. J. Climate, 23: 1334-1353. PDF
• Wang, B., Z. W. Wu, J. P. Li, J. Liu, C. P. Chang, Y. H. Ding, and G. X. Wu, 2008: How to measure the strength of the East Asian summer monsoon. J. Climate, 21, 4449-4462. PDF
• Li, J. P., and Q. C. Zeng, 2005: A new monsoon index, its interannual variability and relation with monsoon precipitation. Climatic and Environmental Research, 10(3): 351-365. PDF　
• Li, J. P., and Q. C. Zeng, 2003: A new monsoon index and the geographical distribution of the global monsoons. Adv. Atmos. Sci., 20, 299-302. PDF 　
• Li, J. P., and Q. C. Zeng, 2002: A unified monsoon index. Geophysical Research Letters, 29(8), 1274, doi:10.1029/2001GL013874. PDF 
• Zeng, Q. C., and  J. P. Li, 2002: On the Interaction between Northern and Southern Hemispheric Atmospheres and the Essence of Tropical Monsoon. Chinese Journal of Atmospheric Sciences, 26, 207-226. PDF
• Li, J. P., and Q. C. Zeng, 2000: Significance of the normalized seasonality of wind field and its rationality for characterizing the monsoon. Science in China (D), 43(6): 647-653. PDF