|Author(s)||Sinha Bablu1, Sévellec Florian2, 3, Robson Jon4, Nurser George1|
|Affiliation(s)||1 : National Oceanography Centre, UK
2 : Laboratoire d'Océanographie Physique et Spatiale, Univ Brest CNRS IRD Ifremer, Brest, France
3 : Ocean and Earth science, University of Southampton, Southampton, UK
4 : National Centre for Atmospheric Science, Dept of Meteorology, University of Reading, UK
|Source||Journal Of Climate (0894-8755) (American Meteorological Society), 2020-09 , Vol. 33 , N. 18 , P. 8025-8045|
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.
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. Publisher's official version : https://doi.org/10.1175/JCLI-D-19-0874.1 , Open Access version : https://archimer.ifremer.fr/doc/00624/73629/