On the relationship between east equatorial Atlantic SST and ISM through Eurasian wave
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The dominant mode of July–August (JA) seasonal variability of Indian summer monsoon rainfall (ISMR) are obtained by performing empirical orthogonal function (EOF) analysis. The first dominant mode of ISMR and its relationships with the sea surface temperature (SST), pressure level wind and geopotential height (GPH) fields are examined using gridded datasets for the period 1979–2014. The principal component of the first leading mode (PC1) obtained in the EOF analysis of JA rainfall over Indian landmass is highly correlated with north-west and central India rainfall, and anti-correlated with east-equatorial Atlantic SST (EEASST). The positive EEASST anomaly intensifies the inter-tropical convergence zone over Atlantic and west equatorial Africa which generates stationary wave meridionally, as meridional transfer of energy is strong, as the influence of background jet-streams are minimal over North Africa and Europe. The anomalous positive and negative GPH are generated over sub-tropics and extra-tropics, respectively, due to the stationary wave. This increases the climatological background steep pressure gradient between sub-tropics and extra-tropics consisting of anomalous negative GPH field over north-west (NW) Europe and vice versa for negative EEASST anomaly. The anomalous positive GPH over NW Europe acts as center of action for the propagation of a Rossby wave train to NW India via Europe consisting of anomalous high over NW of India. This intensifies the Tibetan High westward which reinforces the outbreak of monsoon activities over central and NW India.
KeywordsSouth-west monsoon Indian landmass Tibetan high Rossby wave Empirical orthogonal function Principal component Stationary wave
The author wish to thank to the Editor and two anonymous reviewers for their insightful comments that helped improving the manuscript. The data have been taken from Web sites and all data sources are duly acknowledged. Computational and graphical analyses required for this study have been completed with the free softwares xmgrace, NCL and Ferret.
- Kripalani RH, Kulkarni A (1996) Assessing the impacts of El Nino and non—El Nino related droughts over India. Drought Netw News 8:11–13Google Scholar
- Miller FR, Keshavamurthy RN (1968) Structure of an Arabian Sea summer monsoon system, I.I.O.E. Meteorological Monograph1, (East-West Center Press, Honolulu), 94Google Scholar
- Rajeevan M, Bhate J, Kale JD, Lal B (2006) High resolution daily gridded rainfall data for the Indian region: analysis of break and active monsoon spells. Curr Sci 91:296–306Google Scholar
- Rajeevan M, Gadgil S, Bhate J (2008) Active and break spells of Indian summer monsoon, NCC Research Rep. 7, India Meteorological Department, PuneGoogle Scholar
- Saji NH, Goswami BN, Vinayachandran PN, Yamagata T (1999) A dipole mode in the tropical Indian Ocean. Nature 401:360–363Google Scholar
- Shukla J (1987) Interannual variability of monsoon. In: Fein JS, Stephens PL (eds) Monsoons. Wiley, New York, pp 399–464Google Scholar
- Sikka DR (1980) Some aspects of the large-scale fluctuations of summer monsoon rainfall over India in relation to fluctuations in the planetary and regional scale circulation parameters. Proc Ind Acad Sci (Earth Planet Sci) 89:179–195Google Scholar