Combined interplay of the Atlantic multidecadal oscillation and the interdecadal Pacific oscillation on rainfall and its extremes over Indian subcontinent

摘要

This study provides a pertinent ground for acquiring deeper insight about the low-frequency variability of precipitation and its extremes over India and its homogeneous monsoon regions under the combined interplay of both the Atlantic multidecadal oscillation (AMO) and the interdecadal Pacific oscillation (IPO). The percent of variance in the total/heavy rainfall on decadal-to-multidecadal timescales that can be attributed to these oceanic indices is 88.3/76.7 % for west central and 84.4/72.6 % for northeast regions, which implies that the recent changes in rainfall and it extremes over respective regions is mainly caused by internal natural variability. The opposite phases of AMO and IPO together modulates the total/moderate rainfall over west central and northeast regions in an asymmetric manner; whereas their warm phase stimulates the heavy rainfall over west central region, while their opposite phases together influences the precipitation extremes over northeast region. Based on the projected conditions of these oceanic indices the outlook for west centralortheast regions is fairly good/bad and these regions will experience above-/below-normal precipitation in the upcoming decade or two. The rainfall over northwest region is mainly influenced by the IPO and this region will also likely to receive above-normal precipitation in the upcoming decade or so due to the present cold phase of IPO. Wind circulation pattern divulges that during the warm phase of AMO the southwesterlies over Indian region are strengthened by the equatorial Atlantic winds coming through the equatorial Africa, while in the cold phase of IPO it gets strengthen by the easterlies from the equatorial Pacific.