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Interannual variability of indian summer monsoon arising from interactions between seasonal mean and intraseasonal oscillations

Suhas, E and Neena, JM and Goswami, BN (2012) Interannual variability of indian summer monsoon arising from interactions between seasonal mean and intraseasonal oscillations. Journal of the Atmospheric Sciences, 69 (6). pp. 1761-1774.

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Abstract

Asignificant fraction of interannual variability (IAV) of the Indian summer monsoon (ISM) is known to be governed by "internal" dynamics arising from interactions between high-frequency fluctuations and the annual cycle. While several studies indicate that monsoon intraseasonal oscillations (MISOs) are at the heart of such internal IAV of the monsoon, the exact mechanism through which MISOs influence the seasonal mean monsoon IAV has remained elusive so far. Here it is proposed that exchange of kinetic energy (KE) between the seasonal mean and MISOs provides a conceptual framework for understanding the role of intraseasonal oscillations (ISOs) in causing IAV and interdecadal variability (IDV) of the ISM. The rate of KE exchange between seasonal mean and ISOs is calculated in frequency domain for each Northern Hemispheric summer season over the ISM domain, using 44 yr of the 40-yr ECMWF Re-Analysis (ERA-40) data. The seasonal mean KE and the rate of KE exchange between seasonal mean and ISO shows a significant relationship at both the 850- and 200-hPa pressure levels. Since the rate of KE exchange between seasonal mean and ISO is found to be independent of known external forcing, the variability in seasonal mean KE arising from this exchange process can be considered as an internal component explaining about 20 of IAV and about 50 of IDV. Contrary to the many modeling studies attributing the weakening of tropical circulation to the stabilization of the atmosphere by global warming, this paper provides an alternative view that internal dynamics arising from scale interactions might be playing a significant role in determining the decreasing strength of the monsoon circulation.

Item Type: Article
Additional Information: Copyright of this article belongs to American Meteorological Society.
Uncontrolled Keywords: Annual cycle; Conceptual frameworks; Ecmwf re-analysis; Exchange process; External forcing; Frequency domains; High frequency HF; Indian summer monsoon; Inter-decadal variability; Interannual variability; Internal dynamics; Intraseasonal oscillations; Intraseasonal variability; Modeling studies; Monsoon circulations; Monsoons; Pressure level; Scale interactions; Seasonal mean; Summer season, Atmospheric thermodynamics; Dynamics; Global warming; Upper atmosphere, Tropical engineering, annual cycle; annual variation; decadal variation; kinetic energy; monsoon; seasonal variation; summer
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 27 Dec 2013 07:33
Last Modified: 27 Dec 2013 07:33
URI: http://moeseprints.incois.gov.in/id/eprint/491

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