Influence of Indian Ocean Dipole on Poleward Propagation of Boreal Summer Intraseasonal Oscillations

R. S. Ajayamohan FRCGC, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan

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Suryachandra A. Rao FRCGC, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan

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Toshio Yamagata FRCGC, Japan Agency for Marine-Earth Science and Technology, Yokohama, and Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan

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Abstract

The influence of the Indian Ocean dipole (IOD) on the poleward propagation of boreal summer intraseasonal oscillations (BSISOs) is examined using observed datasets. This study finds that coherent (incoherent) poleward propagation of precipitation anomalies from 5°S to 25°N are observed during negative (positive) IOD years. Disorganized poleward propagation of BSISO in the south equatorial Indian Ocean is observed during positive IOD years. The rationale behind such an anomaly in the poleward propagation of BSISO in contrasting IOD years is identified based on the theory of northward-propagating BSISO, which suggests the influential role of air–sea interaction on the genesis and propagation of BSISO. It is found that the mean structure of moisture convergence and meridional specific humidity distribution undergoes radical changes in contrasting IOD years, which in turn influences the meridional propagation of BSISO. This study assumes significance, considering the critical role of BSISO in modulating the seasonal mean summer monsoon rainfall.

* Current affiliation: Canadian Centre for Climate Modelling and Analysis, Victoria, British Columbia, Canada.

+ Current affiliation: Indian Institute of Tropical Meteorology, Pune, India.

Corresponding author address: R. S. Ajayamohan, Canadian Centre for Climate Modelling and Analysis, University of Victoria, P.O. Box 1700, STN CSC, Victoria, BC V8W 2Y2, Canada. Email: ajayanrs@gmail.com

Abstract

The influence of the Indian Ocean dipole (IOD) on the poleward propagation of boreal summer intraseasonal oscillations (BSISOs) is examined using observed datasets. This study finds that coherent (incoherent) poleward propagation of precipitation anomalies from 5°S to 25°N are observed during negative (positive) IOD years. Disorganized poleward propagation of BSISO in the south equatorial Indian Ocean is observed during positive IOD years. The rationale behind such an anomaly in the poleward propagation of BSISO in contrasting IOD years is identified based on the theory of northward-propagating BSISO, which suggests the influential role of air–sea interaction on the genesis and propagation of BSISO. It is found that the mean structure of moisture convergence and meridional specific humidity distribution undergoes radical changes in contrasting IOD years, which in turn influences the meridional propagation of BSISO. This study assumes significance, considering the critical role of BSISO in modulating the seasonal mean summer monsoon rainfall.

* Current affiliation: Canadian Centre for Climate Modelling and Analysis, Victoria, British Columbia, Canada.

+ Current affiliation: Indian Institute of Tropical Meteorology, Pune, India.

Corresponding author address: R. S. Ajayamohan, Canadian Centre for Climate Modelling and Analysis, University of Victoria, P.O. Box 1700, STN CSC, Victoria, BC V8W 2Y2, Canada. Email: ajayanrs@gmail.com

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