Teleconnections of Tropical Pacific and Indian Ocean Oscillations with Monsoon Rainfall Variability over Southern Slope of the Central Himalayas

Abstract:

The inter-annual variability of monsoon rainfall over southern slope of the Himalayas (MROSSH) is largely affected by tropical Pacific and Indian Ocean oscillation because these large scale oceanic dynamics have pronounced impact on regional circulation over South Asia. Here we have tried to establish statistical relationship among Pacific and Indian Ocean Oscillations and MROSSH. Appropriate indices for ENSO, Indian Ocean dipole (IOD), Walker and Hadley circulations have been applied and their connection with MROSSH was investigated.

Analysis of APHRODITE data for the period 1979-2007 suggested the great spatial and temporal variation with 9 to 11 years cyclic oscillation, however, no clear trend was observed over the study period. Strong negative correlation is observed between MROSSH and Nino3.4 index (r=-0.50, p<0.01). IOD events have significant impact on MROSSH with countering effect over ENSO. The impact of El Nino (La Nina) on MROSSH is largely reduced by PIOD (NIOD) when composite of co-occurring El Nino-PIOD and La-Nina-NIOD is considered. There was a strong negative association (r=-0.589, p<0.01) between zonal Walker and meridional Hadley circulation. Both of those of tropical circulation were found to be tightly coupled with MROSSH. In particular MROSSH is positively correlated with Walker circulation (r=0.69, p<0.01) and negatively correlated with Hadley circulation (r=-0.632, p<0.01). In summary, the dynamic behavior and inter-annual variability of MROSSH is largely affected by tropical Pacific and Indian Ocean oscillation and associated atmospheric teleconnections.