Impact of El Nino & La Nina on Indian Monsoon

There is a general association between El Nino and monsoon drought for South Asia. What is this El Nino factor? How far it is influencing the monsoon of our country? Prof. (Dr.) C.KRajan, Chair for Climate / Environmental Changes , SCMS Cochin School of Business, explains all about this
intriguing environmental issue. Dr. Rajan who has published 75 research papers and few books was Former Director of Centre for Monsoon Studies, CUSAT.El-Nino-weather-phenomenon

El Nino is a phenomenon which exists from ancient times. It was discovered clearly only in recent times by using sensors put on satellites. At first, El Nino was viewed as a local phenomenon. In the 1950s and 1960s, however, data became available on oceanic conditions across the entire Pacific, and oceanographers realised that the unusual conditions were not confined to the coast of Peru and Ecuador. The warm surface waters that appear there are only one aspect of changes in the oceanic circulations of the entire tropical Pacific Ocean, which significantly alter the sea-surface temperature patterns of the Pacific.

There is a general association between El Nino and monsoon drought for South Asia (and La Nina with monsoon flood). One of the main mechanisms involved is via perturbations to the Walker Circulation. So, an El Nino warming, which generates anomalous precipitation and hence ascent in the central-to-east Pacific also generates anomalous subsidence over the Indian Ocean region. This acts to suppress convection, providing a large and seasonal-scale background on which the monsoon can operate. Though monsoon is experienced during June to September, El Nino Southern Oscillation (ENSO) normally peaks in December-February. So how do we choose which year to refer to an ENSO event?

The answer for South Asia is normally in the ENSO developing year – in other words, the summer before the ENSO peak. So, El Ninos developed in 2002 and 2009, for example, affected the monsoons in those years. There is growing evidence of diversity in types of El Nino events, which is commonly referred to as traditional/East Pacific El Nino versus Central Pacific El Nino. These latter events are thought to have a larger impact on the Indian monsoon. Hence, the relatively small but central Pacific events like 2002 and 2009 have a large influence on monsoon drought, whereas the large East Pacific event of 1997 does not. Whatever the large, seasonal-scale forcing, intra-seasonal variability can give much greater variance in monsoon rainfall.

(Read the full article in the July Issue of Safety Messenger Magazine 2015 )

Author: SubEditor

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