Giorgio Graffino, Riccardo Farneti, Fred Kucharski, Franco Molteni

The importance of subtropical and extratropical zonal wind stress on Pacific Subtropical Cells (STCs) strength is assessed through several idealized numerical experiments performed with a global ocean model. Different zonal wind stress anomalies are employed, and their intensity is strengthened or weakened with respect to the climatological value throughout a suite of simulations.
Strengthened (weakened) zonal wind stress anomalies result in increased (decreased) STCs meridional mass and energy transport. Upwelling of subsurface water into the tropics is intensified (reduced), a distinct cold (warm) anomaly appears in the equatorial thermocline and up to the surface, resulting in significant tropical sea surface temperature (SST) anomalies.
Results hold for both subtropical and extratropical anomalies, suggesting the potential impact of mid-latitude atmospheric modes of variability on tropical climate.
Finally, the remotely-driven response is compared with a set of locally-forced simulations, where an equatorial zonal wind stress anomaly is imposed. A dynamically distinct response is achieved, whereby the equatorial thermocline adjusts to the wind stress anomaly resulting in significant equatorial SST anomalies as in the remotely-forced simulations. Significant anomalies in the Indonesian throughflow are generated only when equatorial wind stress anomalies are applied, leading to remarkable heat content anomalies in the Indian Ocean.
Equatorial wind stress anomalies experiments do not involve modifications of STC transports, but could set up the appropriate initial conditions for a tropical-extratropical teleconnection, involving both Hadley cells and STC anomalous transports.