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Indian summer monsoon intra-seasonal oscillation associated with the developing and decaying phase of El Nino

Pillai, PA and Chowdary, JS (2016) Indian summer monsoon intra-seasonal oscillation associated with the developing and decaying phase of El Nino. International Journal of Climatology, 36 (4). pp. 1846-1862.

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Abstract

The present study investigates the characteristics of active and break cycles associated with the Indian summer monsoon (ISM) during developing and decaying phase of El Niño and in the years in which Indian Ocean Dipole (IOD) co-occurred with El Niño (co-occurred years). Observations show that break days are more in number (∼2–3 times) and long lasting (∼15–20 days) than active days in El Niño developing summers and vice versa for decay years. During El Niño developing years, northward propagation is well organized with significant anomalies in both active and break phases. The increased convection associated with active phase persists longer over Indian Ocean, than over the monsoon region, while the reduced convection in break phase propagates faster from ocean to land and persists there for a longer time. Compared to break events, active events have slower (faster) propagation over the monsoon (oceanic) region during El Nino decay years. The present study put forward the argument that the contrasting persistent circulations over Indo-western Pacific regions favour particular phase of intra-seasonal oscillation (ISO) in developing and decay phase of El Nino. These long-lasting circulations advect anomalous dry (moist) air to ISM region for longer period, resulting in long-lasting break (active) events in El Niño developing (decay) years. During co-occurrence years, the number of break (active) days is reduced by two to three times compared to the developing (decaying) phase of El Niño. It is found that 30- to 60-day scale ISO is strongly modulated, than 10 - to 20-day scale, by the changes in seasonal mean state associated with El Nino. Thus, this study demonstrates that the ISO characteristics such as its variance, northward propagation, spatial distribution and duration of active and break days are strongly modulated by seasonal background anomalies over the Indo-Pacific region.

Item Type: Article
Additional Information: Copyright of this article belongs to Royal Meteorological Society
Uncontrolled Keywords: Indian summer monsoon;intra-seasonal oscillation;El Niño;northward propagation;background anomalies;active–break cycles
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 08 Apr 2017 09:11
Last Modified: 08 Apr 2017 09:11
URI: http://moeseprints.incois.gov.in/id/eprint/4353

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