Indian Journal of Science and Technology

Abstract

In this paper the relationship between the two dominant modes of the atmospheric low frequency oscillation viz. ENSO (El Nino Southern Oscillation) and NAO (North Atlantic Oscillation) is examined prior to the onset of the Indian summer monsoon season (June-September) and during the monsoon period. The analysis is carried out for 107 years of data (1881-1987). From the analysis it is observed that relationship between ENSO and NAO is an inverse before the monsoon season starts and during the monsoon season the relationship between these low frequency modes is direct. The relationship again becomes the inverse after the withdrawal of the monsoon. Behaviour of these two oscillations are monitored for the contrasting monsoon years (i.e. deficient and excess monsoon years). The study reveals that these two oscillations are improper phase in deficient monsoon years but in excess monsoon years these oscillations are in proper phase.

Key words: North Atlantic Oscillation, Southern Oscillation and Indian summer monsoon