On the Weakening Relationship Between the Indian Monsoon and ENSO

Abstract

Analysis of the 140-year historical record suggests that the inverse relationship between the El Nino-Southern Oscillation (ENSO) and the Indian summer monsoon (weak monsoon arising from warm ENSO event) has broken down in recent decades. Two possible reasons emerge from the analyses. A southeastward shift in the Walker circulation anomalies associated with ENSO events may lead to a reduced subsidence over the Indian region, thus favoring normal monsoon conditions. Additionally, increased surface temperatures over Eurasia in winter and spring, which are a part of the midlatitude continental warming trend, may favor the enhanced land-ocean thermal gradient conducive to a strong monsoon. These observations raise the possibility that the Eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal level despite strong ENSO events.

Interdecadal change of the boreal summer circumglobal teleconnection (1958–2010)

“…In particular, the ENSO property including period, amplitude, spatial structure, and propagation has been changed [Wang, 1995;An and Wang, 2000], and the ENSO-ISM relationship has weakened [Kumar et al, 1999] but the ENSO-WNP/EASM relationship strengthened [Wang et al, 2008a]. A natural question arises as to whether the tropicalextratropical teleconnection has been changed associated with this global climate regime shift.…”

Combining regional moist static energy and ENSO for forecasting of early and late season Indian monsoon rainfall and its extremes

“…Yet the strong correlation that existed before~1980 has subsequently shrunk and become insignificant [Krishna Kumar et al, 1999]. Although this diminished correlation has brought some understanding of how different parts of the tropical Pacific relate to monsoon rainfall [Krishna Kumar et al, 2006], the weakened correlation has made prediction difficult.…”

“…Linear regression is the standard method used, but nonlinear and multimodel combination methods have been proposed [Rajeevan et al, 2007], and regardless, the skills are limited by the strength of the predictors to monsoon rainfall. Although a combination of such predictors once engendered optimism [e.g., Shukla and Mooley, 1987], marked variations in correlations with ENSO indices in recent years cast doubt on such predictors [e.g., Krishna Kumar et al, 1999Kumar et al, , 2006. In general, such predictors when applied to the entire monsoon season account for less than 20% of the variance in observed monsoon rainfall over India [e.g., Delsole and Shukla, 2002].…”

Perspectives on the non-stationarity of the relationship between Indian and East Asian summer rainfall variations

“…Given the impact of ENSO on both Indian and East Asian summer monsoon variability (Wang, Wu, and Lau 2001), ENSO is likely a factor involved in the long-term changes in the Indian-East Asian summer rainfall relationship through changes its impacts on either the Indian or East Asian summer monsoon (Kumar, Rajagopalan, and Cane 1999;Wu and Wang 2002). Hu et al (2005) indicated that ENSO may reinforce the connection between Indian and North China summer rainfall variations.…”