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Surging of global surface temperature due to decadal legacy of ocean heat uptake

Sinha, Bablu; Sévellec, Florian; Robson, Jon; Nurser, George. 2020 Surging of global surface temperature due to decadal legacy of ocean heat uptake. Journal of Climate, 33 (18). 8025-8045. https://doi.org/10.1175/JCLI-D-19-0874.1

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Abstract/Summary

Global surface warming since 1850 consisted of a series of slowdowns (hiatus) followed by surges. Knowledge of a mechanism to explain how this occurs would aid development and testing of interannual to decadal climate forecasts. In this paper a global climate model is forced to adopt an ocean state corresponding to a hiatus (with negative Interdecadal Pacific Oscillation, IPO, and other surface features typical of a hiatus) by artificially increasing the background diffusivity for a decade before restoring it to its normal value and allowing the model to evolve freely. This causes the model to develop a decadal surge which overshoots equilibrium (resulting in a positive IPO state) leaving behind a modified, warmer climate for decades. Water mass transformation diagnostics indicate that the heat budget of the tropical Pacific is a balance between large opposite signed terms: surface heating/cooling due to air-sea heat flux is balanced by vertical mixing and ocean heat transport divergence. During the artificial hiatus, excess heat becomes trapped just above the thermocline and there is a weak vertical thermal gradient (due to the high artificial background mixing). When the hiatus is terminated, by returning the background diffusivity to normal, the thermal gradient strengthens to pre-hiatus values so that the mixing (diffusivity x thermal gradient) remains roughly constant. However, since the base layer just above the thermocline remains anomalously warm this implies a warming of the entire water column above the trapped heat which results in a surge followed by a prolonged period of elevated surface temperatures.

Item Type: Publication - Article
Digital Object Identifier (DOI): https://doi.org/10.1175/JCLI-D-19-0874.1
ISSN: 0894-8755
Date made live: 11 Jun 2020 13:28 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/527944

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