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Volume 9, issue 1 | Copyright
Earth Syst. Dynam., 9, 285-297, 2018
https://doi.org/10.5194/esd-9-285-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Mar 2018

Research article | 20 Mar 2018

Sensitivity of the tropical climate to an interhemispheric thermal gradient: the role of tropical ocean dynamics

Stefanie Talento1,2 and Marcelo Barreiro1 Stefanie Talento and Marcelo Barreiro
  • 1Department of Atmospheric Sciences, Institute of Physics, Universidad de la República, Montevideo, 11400, Uruguay
  • 2Department of Geography, Climatology, Climate Dynamics and Climate Change, Justus Liebig University of Giessen, 35390  Giessen, Germany

Abstract. This study aims to determine the role of the tropical ocean dynamics in the response of the climate to extratropical thermal forcing. We analyse and compare the outcomes of coupling an atmospheric general circulation model (AGCM) with two ocean models of different complexity. In the first configuration the AGCM is coupled with a slab ocean model while in the second a reduced gravity ocean (RGO) model is additionally coupled in the tropical region. We find that the imposition of extratropical thermal forcing (warming in the Northern Hemisphere and cooling in the Southern Hemisphere with zero global mean) produces, in terms of annual means, a weaker response when the RGO is coupled, thus indicating that the tropical ocean dynamics oppose the incoming remote signal. On the other hand, while the slab ocean coupling does not produce significant changes to the equatorial Pacific sea surface temperature (SST) seasonal cycle, the RGO configuration generates strong warming in the central-eastern basin from April to August balanced by cooling during the rest of the year, strengthening the seasonal cycle in the eastern portion of the basin. We hypothesize that such changes are possible via the dynamical effect that zonal wind stress has on the thermocline depth. We also find that the imposed extratropical pattern affects El Niño–Southern Oscillation, weakening its amplitude and low-frequency behaviour.

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In a series of simulations, with models of different complexity, we analyse the role of the tropical ocean dynamics in the transmission of information when an extratropical thermal forcing is imposed. In terms of annual means we find that the tropical ocean dynamics oppose the remote extratropical signal. However, changes in the sea surface temperature seasonal cycle in the equatorial Pacific Ocean become significant only once the tropical ocean dynamics are incorporated.
In a series of simulations, with models of different complexity, we analyse the role of the...
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