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The role of Amazon river runoff on the multidecadal variability of the Atlantic ITCZ

Jahfer, S and Jahfer, S and Vinayachandran, PN and Vinayachandran, PN and Nanjundiah, RS and Nanjundiah, RS and Nanjundiah, RS (2020) The role of Amazon river runoff on the multidecadal variability of the Atlantic ITCZ. In: Environmental Research Letters, 15 (5).

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Official URL: https://dx.doi.org/10.1088/1748-9326/ab7c8a


Climate model projections for the 21st century predict an elongated dry season in the Amazon basin, potentially reducing the discharge into the equatorial Atlantic Ocean. In order to understand the climatic role of Amazon runoff into the ocean, sensitivity experiments were carried out using the Community Earth System Model (CESM). Without Amazon runoff, the Atlantic Meridional Overturning Circulation (AMOC) strengthens and the associated increase in northward heat transport induces a positive temperature anomaly in the North Atlantic Ocean with a spatial structure similar to the positive phase of the Atlantic Multidecadal Variability (AMV). A positive phase of AMV developed in the absence of Amazon runoff triggers a bipolar seesaw in SST across the thermal equator with warming to the north and cooling to the south. The boreal summer rainfall in the tropical Atlantic Ocean sector responds to this change in SST by displacing the intertropical convergence zone (ITCZ) to the north of its mean position. An alternate experiment by doubling the Amazon runoff shows a weakening of AMOC and AMV and a southward shift in the summer-time ITCZ. In both the experiments, we find that the largest change in rainfall is exhibited over the region where the AMV-induced decadal variability in rainfall is prominent, confirming the source of rainfall variability. Based on sensitivity experiments by varying the runoff, we propose that the Amazon discharge can affect the multidecadal variabilities, the AMOC and AMV, and thereby the low-frequency variability of rainfall over the tropical North Atlantic Ocean and northwest Africa. We conclude that the freshwater input from the Amazon plays a significant role in the sustained wet and dry climatic phases of rainfall events over the tropical North Atlantic Ocean and West African nations and thus have an impact on the regional hydrological cycle and economy. © 2020 The Author(s). Published by IOP Publishing Ltd.

Item Type: Journal Article
Publication: Environmental Research Letters
Publisher: Institute of Physics Publishing
Additional Information: Copy right for this article belongs to Institute of Physics Publishing
Keywords: Climate models; Rain; Runoff; Tropics, Atlantic meridional overturning circulations; Decadal variability; Intertropical convergence zone; Low frequency variability; Multidecadal variability; North Atlantic Ocean; Rainfall variability; Temperature anomaly, Oceanography, air-sea interaction; decadal variation; intertropical convergence zone; runoff, Amazon River; Atlantic Ocean
Department/Centre: Division of Mechanical Sciences > Divecha Centre for Climate Change
Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited: 26 Nov 2020 10:45
Last Modified: 26 Nov 2020 10:45
URI: http://eprints.iisc.ac.in/id/eprint/66051

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