For well over 300 years, the monsoon has been considered to be a gigantic land–sea breeze driven by the land–ocean contrast in surface temperature. In this paper, this hypothesis and its implications for the variability of the monsoon are discussed and it is shown that the observations of monsoon variability do not support this popular theory of the monsoon. An alternative hypothesis (whose origins can be traced to Blanford’s (1886) remarkably perceptive analysis) in which the basic system responsible for the Indian summer monsoon is considered to be the Intertropical Convergence Zone (ITCZ) or the equatorial trough, is then examined and shown to be consistent with the observations. The implications of considering the monsoon as a manifestation of the seasonal migration of the ITCZ for the variability of the Indian summer monsoon and for identification of the monsoonal regions of the world are briefly discussed.
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It is a pleasure to acknowledge the monsoon experts, the late D R Sikka, Drs T N Krishnamurti and P V Joseph, from whom I have learnt a great deal, stimulating discussions over many years with Profs J Srinivasan, G S Bhat, Ravi Nanjundiah and other colleagues at CAOS and insights gained from comments of Profs Mark Cane and S G H Philander, contributed significantly to my understanding of the monsoon problem. This paper could not have been written without the fruitful interaction with Drs P A Francis, Sajani Surendran and K Rajendran. A detailed and careful review by Dr D Shankar and useful suggestions by the reviewers helped considerably in improving the paper.
Corresponding editor: N V Chalapathi Rao
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Gadgil, S. The monsoon system: Land–sea breeze or the ITCZ?. J Earth Syst Sci 127, 1 (2018). https://doi.org/10.1007/s12040-017-0916-x
- Indian summer monsoon
- monsoonal regions
- intertropical convergence zone
- equatorial trough
- heat lows