Northeast monsoon rainfall variability over south peninsular India vis‐à‐vis the Indian Ocean dipole mode

Abstract

Whereas the June through to September southwest summer monsoon season over the Indian subcontinent has been the main focus of research, the October through to December northeast monsoon season over south peninsular India has received less attention. Hence, this study focuses on the northeast monsoon rainfall (NEMR) variability using historical data for a 131 year period and its relationship with the neighbouring Indian Ocean sea-surface temperature (SST).Based on the observed available rainfall data, a time series of NEMR over the coherent south peninsular India has been developed. Similarly, an index to quantify the Indian Ocean dipole mode (IODM), exhibiting warm (cool) waters over the equatorial western (southeastern) Indian Ocean, has been developed using GISST data for the same period. The dynamics of the NEMR-IODM relationship are examined with the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis data.Interannual and decadal variabilities in NEMR reveal alternate epochs of above-and below-normal rainfall. The epochs tend to last for about a decade or two. Rainfall epochs near the equatorial Indian Ocean tend to last for about a decade. No long-term trends in NEMR are noted. On the other hand, the decadal variability in the IODM reveals a dominance of the negative phase during the earlier decades (1880-1920) and a positive phase during recent decades , with suppressed activity in between. Long-term variability in the IODM clearly reveals an increasing trend, which could be related to greenhouse warming. Further, the NEMR variability is enhanced during the decades when the IODM exhibits its active phase, and is suppressed during the decades when the IODM is inactive.The NEMR and the IODM are directly related, suggesting that the positive (negative) phase enhances (suppresses) the northeast monsoon activity. During the positive phase, the anomalous flow pattern shows winds converging and suggesting moisture transport from the southeast Indian Ocean and the Bay of Bengal towards south peninsular India. In contrast, the negative phase reveals winds diverging and transporting moisture away from the south Indian region. The anomalous SST and circulation features associated with the positive IOD/excess rainfall and negative IOD/deficient rainfall are consistent and clearly bring out the coupled ocean-atmosphere dynamics over the Indian Ocean. These results show the direct influence of the IODM phenomenon on the interannual and decadal NEMR variability over south India.

Northeast monsoon over India: variability and prediction

“…Kripalani and Kumar (2004) showed that the IOD also influences the NEMR variability. In this section, the ENSEMBLES MME results were analysed to examine whether the ENSEMBLES MME captures the observed relationship with ENSO and IOD.…”

“…significantly above normal (63% and 55% respectively). The increasing trend in the NEMR during the recent years could be related to the increasing trend in the positive phase of the Indian Ocean Dipole Mode (Kripalani and Kumar, 2004). The inter-annual variability of the NEMR is linked to the El Niño/Southern Oscillation (ENSO), Indian Ocean Dipole and the EQUINOO (De and Mukhopadhyay, 1999;Bhanu Kumar et al, 2004;Kripalani and Kumar, 2004;Zubair and Ropelewski, 2006;Kumar et al, 2007;Sreekala et al, 2011).…”

“…Studies of the NEMR variability are limited (Ramaswamy, 1972;Dhar and Rakhecha, 1983;Singh and Sontakke, 1999;Balachandran et al, 2006). Some of the previous studies related the NEMR variability with ocean-atmosphere phenomena such as El Niño/Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) (Bhanu Kripalani and Kumar, 2004;Zubair and Ropelewski, 2006;Kumar et al, 2007). Some recent studies have shown that the interannual variability of the NEMR is significantly influenced by ENSO and that this relationship has strengthened during the recent years.…”

“…Seasonal monsoon rainfall (in cm) during the northeast monsoon season (October to December) averaged over the period 1951-2004. to stronger easterly wind anomalies and anomalous low-level moisture convergence over the north Indian Ocean. Kripalani and Kumar (2004) have shown that the NEMR over the south peninsula and the IOD mode are directly related, suggesting that the positive (negative) phase of the IOD enhances (suppresses) the northeast monsoon activity. Balachandran et al (2006) have examined the local and teleconnective association between the NEMR and the global surface temperature anomalies (STAs) using the monthly gridded surface air temperature data for the period 1901-2004.…”

Decadal variability of the Indian Ocean dipole

“…Several theories have been proposed for this decadal ENSO (see Zhang et al [1997] and Luo et al [2003] for details and references). Recently, Kripalani and Kumar [2004] found decadal epochs in seasonally stratified IOD index. In this context, we here examine the possibility of the existence of a decadal IOD using observed data sets and a coupled general circulation model (CGCM).…”