Tropical response to extratropical forcing in a coupled climate model: A comparison between the Atlantic and Pacific Oceans

The tropical ocean response to the extratropical forcing is quantitatively estimated using a coupled climate model. This work compares the responses in tropical Atlantic and tropical Pacific. For the tropical sea surface temperature (SST), the response magnitudes in the tropical Atlantic and Pacific are comparable. However, for the tropical thermocline temperature, the response in the Atlantic can be two times of that in the Pacific. The maximum temperature change in the tropical Pacific is located in the east and at the depth of around 200 m, which is mainly related to the eastern boundary shallow subduction from the extratropical Southern Pacific. The maximum temperature change in the tropical Atlantic is located in the west and at the depth of about 500 m, well below the equatorial thermocline in the Atlantic. This may be related to the western boundary Kelvin wave propagating from the Northern midlatitude Atlantic. The Kelvin waves can be generated by the anomalous Ekman downwelling in the mid-high latitude and propagate along the intermediate isopycnal level outcropped there. The different responses in the tropical Atlantic and Pacific are also closely related to the different changes in the meridional overturning circulations. The Pacific shallow overturning circulations (or the subtropical cells, STCs) are nearly symmetrical to the equator and tend to change symmetrically to the external forcing. The Atlantic overturning circulation is much more complicate because it consists of two components: the shallow STCs and the deep meridional overturning circulations. The interaction between them makes the tropical Atlantic oceanic response to extratropical forcing more nonlinear.