Atlantic Niño modulation of the Indian summer monsoon through Asian jet

Abstract The Indian rainfall and the Atlantic Niño peaks during summer month and have inverse relationship. This relationship has been revisited in the current study and it is found that the Atlantic Niño significantly influences a dipole pattern of rainfall in the north–east and the north-western parts of India. The positive phase of the Atlantic Niño intensifies the inter-tropical convergence zone, as a result of this local tropospheric warming, over the equatorial east Atlantic and west Africa, owing to the enlargement of the upper-troposphere divergence. This provokes meridional stationary wave owing to the stronger meridional transfer of energy, as the influences of background jet-streams are minimal over North Africa and Europe. This results in the consecutive anomalous negative, positive, and negative geopotential heights (GPHs) over the tropical east Atlantic, Mediterranean, and north–west Europe, respectively. The north–west Europe acts as the center of action for the propagation of a Rossby wave train zonally oriented toward central Asia reinforcing positive GPH anomaly over there. The positive GPH anomaly reduces the Asian subtropical westerly jet-stream east of the Caspian Sea, owing to the reduction in the upper-troposphere divergence toward the Indian subcontinent and caused for above (below) normal north–east (north–west) Indian summer monsoon rainfall. The atmospheric general circulation model captures general characteristics of wave pattern and changes in the Asian jet when correlated with Atlantic Niño with considerable skill.