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On factors responsible for recent secular trend in the onset phase of monsoon intraseasonal oscillations

Goswami, BN and Kulkarni, JR and Mujumdar, VR and Chattopadhyay, R (2010) On factors responsible for recent secular trend in the onset phase of monsoon intraseasonal oscillations. International Journal of Climatology, 30 (14). pp. 2240-2246.

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Abstract

The timing of the dramatic 'onset' and subsequent northward progression of the Indian summer monsoon (ISM) are unique features of the monsoon annual cycle and are strongly linked to planning of agricultural activity and water management. Here, we show that the northward propagation of the first episode of intraseasonal oscillation (ISO) associated with the onset phase of ISM has slowed down significantly during the past decade compared with prior decades. The slowdown is due to systematic weakening of two regional climatic features responsible for northward progression of the tropical convergence zone (TCZ) namely, the vertical easterly wind shear and the north-south gradient of the mean low-level humidity around the equator. Eastward shift of the Walker circulation associated with increasing strength of El Ninos appears to be responsible for weakening of the vertical wind shear over Indian monsoon region. The slow northward propagation during recent decades leads to a climatological sub-seasonal oscillation representing a predictable component of the onset phase of the ISM.

Item Type: Article
Additional Information: Copyright of this article belongs to Royal Meteorological Society
Uncontrolled Keywords: Agricultural activities; Annual cycle; Climatic features; Convergence zones; Indian monsoon; Indian summer monsoon; Intraseasonal oscillations; Monsoon onset; Regional-large scale mechanism; Secular trend; Trends; Unique features; Vertical wind shear; Walker circulation; Wind shears, Atmospheric thermodynamics; Planning; Water management, Tropical engineering, climate oscillation; monsoon; regional climate; trend analysis; Walker circulation; wind shear
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 28 May 2015 10:58
Last Modified: 28 May 2015 10:58
URI: http://moeseprints.incois.gov.in/id/eprint/766

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