The Recent Role of the Indian Ocean to ENSO Diversity

Increased warming of the Indian Ocean SST influences the tropical atmosphere by strengthening the Pacific Walker circulation, which intensifies the easterly trade winds and thereby increases the ocean heat content and sea level in the western tropical Pacific.

In order to see the mechanisms that result from the persistent warming an experiment whereby the heat flux over the Indian Ocean only is increased in a fully coupled model, mimicking the observed decadal trend, possibly due to the effects of greenhouse warming. The model was run for a hundred years and compared to a control run that differs only in the addition of the increased heat flux over the Indian Ocean. The main result is to see an increase in the easterlies over the western tropical Pacific as well as a westward shift and a weakening of the ENSO variance, as in central Pacific (CP) El Ninos.

From 1980-2000 was a period of strong east Pacific (EP) ENSOs, whereas following the 1999 La Nina until 2014 has been a period of CP ENSOs. In order to better understand the characteristics of CP and EP ENSOs two experiments were conducted. Using a fully coupled GCM two 100-year flux adjusted experiments were made, one based on 1980-2000 and the other on 2001-2014. The results of these experiments along with a comparison to the warm Indian Ocean experiment will be presented.

Within the context of these studies will be comments on the 2014 and 2015 ENSO forecasts.