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

Goswami, B. N. ; Kulkarni, J. R. ; Mujumdar, V. R. ; Chattopadhyay, R. (2009) On factors responsible for recent secular trend in the onset phase of monsoon intraseasonal oscillations International Journal of Climatology . ISSN 0899-8418

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Official URL: http://onlinelibrary.wiley.com/doi/10.1002/joc.204...

Related URL: http://dx.doi.org/10.1002/joc.2041

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
Source:Copyright of this article belongs to John Wiley and Sons, Inc.
Keywords:Monsoon Onset Phase; Intraseasonal Oscillation; Trends; Regional-large Scale Mechanism
ID Code:23841
Deposited On:01 Dec 2010 13:02
Last Modified:02 Jun 2011 08:09

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