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A Gill-type mechanism for rainfall initiation over the rainshadow region
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  • Mohan S Thota,
  • Niranjan Kumar Kondapalli,
  • Madhulatha Akkisetti,
  • Rajeevan M
Mohan S Thota
National Centre for Medium Range Weather Forecasting

Corresponding Author:drmohanthota@gmail.com

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Niranjan Kumar Kondapalli
Atmosphere and Ocean Research Institute
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Madhulatha Akkisetti
Korean Institute of Atmospheric Prediction System
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Rajeevan M
Ministry of Earth Sciences
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This novel study explains a physical mechanism for the rainfall initiation over the southeast peninsular India (SEPI, referred to be a ‘rain shadow’ region) during the southwest monsoon season. Further, the contrasting rainfall patterns between the rain shadow region and central India (CI,) are also elucidated through the response of the maritime continent (MRC) convection. The MRC is found to be a prominent source for the initiation of wet spells over the rain shadow region (during which CI is in dry phase), with the rainfall anomalies over MRC leads SEPI by ~5-7 days. Evolution of convective anomalies resembles a classical Gill-type response, with a pair of Rossby waves on the poleward side of the convection center and Kelvin waves on the eastern side. Thus, the combined effect of large-scale circulation and moisture anomalies over MRC contributes to the preconditioning and subsequent positive rainfall anomalies over the rain shadow region.