Abstract
The present study addresses the depiction of regional features in the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) real-time products associated with the onset of Indian summer monsoon 2006 along the west coast of India. This study attempts to understand some atmospheric dynamical processes that give rise to the northward shifting of the convergence zones in the sub-daily scale leading to the onset over Mumbai. The comparison of analysis and forecast shows that NCEP GFS appears to follow the analysis till 24 h, but deviates thereafter. The most notable feature in analyses is the distinct meridional asymmetries in the vorticity field with respect to the convection center. It is identified that the equivalent barotropic structure of vorticity north of the convection center is the main forcing for the northward movement of convergence zones. The composite meridional–vertical structure of each term in the vorticity budget reveals the importance of convective term in the upper atmosphere (700–200 hPa) and the stretching term in the lower atmosphere (1,000–700 hPa) with a lesser contribution of the tilting term. From an analysis of a simplified vorticity equation by retaining these dominant terms and by comparing the evolution of the diabatic heating, it is concluded that the inaccuracies in the model’s representation of convection led to the weakening of barotropic westerlies in the forecast.
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Acknowledgments
The authors are thankful to Director Indian Institute of Tropical Meteorology for providing all necessary infrastructural facilities. They would also like to thank the anonymous reviewers for their constructive comments, which improved the quality of the study. The authors wish to thank the National Centers for Environmental Prediction, USA for online access to their Global Forecast System real-time products. The use of daily weather charts and reports published by the India Meteorological Department is acknowledged with thanks. The Grid Analysis and Display System (GrADS) used for preparing diagrams is gratefully acknowledged.
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Taraphdar, S., Sanjay, J. & Mukhopadhyay, P. On northward movement of convergence zones along west coast of India in a real-time forecast. Meteorol Atmos Phys 104, 177–189 (2009). https://doi.org/10.1007/s00703-009-0025-8
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DOI: https://doi.org/10.1007/s00703-009-0025-8