Abstract
Palghat gap (~ 76.5°E; 10.75°N) is a narrow gap in the Western Ghats mountain chain of south India. Strong westerly winds flow from its exit during the Indian summer monsoon season (June to September, JJAS). Climatological three-dimensional structure of these exit winds is presented using thirty years (1983–2012) ‘Indian Monsoon Data Assimilation and Analysis’ regional reanalysis data. These exit winds initially accelerate, attain their maximum speed around 77.5°E, slow down thereafter. This wind flow is prominently seen between the surface and ~ 700 hPa in the vertical, ~ 77°E and ~ 80°E in the zonal and ~ 10.5°N and 11.5°N in the meridional directions. We refer these strong winds as the Palghat Gap Exit Jet (PGEJ). Core of the PGEJ is found ~ 950 hPa with its axis passing along ~ 10.8°N. Direction of the PGEJ is steady throughout JJAS. To understand the possible reasons behind the formation of PGEJ, detailed analysis using four years (2009–2012) of reanalysis data is carried out. PGEJ fluctuates from diurnal to intraseasonal (30–60 days) time scales. On diurnal scale, strength and zonal extent of the PGEJ are stronger and wider respectively around mid-night whereas weaker and shorter respectively around noon. Also, PGEJ is shallow during night but relatively deeper during day. On intraseasonal time scale, PGEJ is stronger (weaker) than its seasonal mean strength during active (break) monsoon phase. Besides, PGEJ becomes stronger when synoptic scale monsoon low-pressure systems pass over the northwest Bay of Bengal and adjoining monsoon trough region. Presence of PGEJ only during JJAS with characteristic variabilities of the Indian summer monsoon and its close association with monsoon trough collectively suggest that it is an integral part of the Indian summer monsoon circulation.
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Data availability
The data sets used for this study are available at (i) https://rds.ncmrwf.gov.in, (ii) https://mosdac.gov.in, and (iii) https://climate.copernicus.eu.
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Acknowledgements
We sincerely thank the Director, Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram for his keen interest and useful discussions during the study. We are thankful to NCMRWF and ERA for providing reanalysis data. BS and SS thankfully acknowledge their research studentship offered by Vikram Sarabhai Space Centre, Thiruvananthapuram.
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Sathiyamoorthy, V., Swathi, B. & Samuel, S. Characteristics of the strong winds on the exit region of the Palghat gap during the Indian summer monsoon season. Clim Dyn 62, 239–255 (2024). https://doi.org/10.1007/s00382-023-06915-3
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DOI: https://doi.org/10.1007/s00382-023-06915-3