The Non-Linear Interplay Among ENSO, ENSO Modoki, IOD and Monsoon
Abstract:The El Nino/Southern Oscillation (ENSO), ENSO Modoki and Indian Ocean Dipole (IOD) have distinct impacts on the climate variation of the Indian Ocean rim countries. The Indian summer monsoon rainfall is seen to be positively influenced by the positive phase of the IOD and in recent decades it could reduce the effects arising from concurrent El Nino events of the Pacific. Unlike the positive influences on the summer rainfall arising from the positive IOD events, a proportionate opposite relationship is not observed for some of the negative IOD events, for example, the events of 2005 and 2013. The teleconnections arising from negative IODs to East Asia, particularly associated with La Ninas, appear somewhat similar to that of positive IOD events. This non-linearity stems from the complex interactions among the phenomena of the tropical Indian and Pacific Oceans; such as the phases of IOD and ENSO, and their concurrences. Also, the unique land-sea distribution in the Indian Ocean and associated stronger than normal atmospheric convections over India and surrounding seas contribute to this non-linearity.
The Southeast Asian monsoon is on the other hand seen to be influenced by tropical and extra tropical climate variations. ENSO and ENSO Modoki usually dominate the rainfall variability during spring and fall seasons. However, regional monsoon and extratropical climate modes influence the rainfall variations during summer and winter seasons, respectively. While the associated monsoon variability, which mostly arises in the Indian Ocean, is easier to understand and predict, the associated extratropical climate variations in winter (such as the Siberian and High and Aleutian Low) are difficult to comprehend and predict owing to their non-linear interactions with other modes of climate variations.