Vertical energy flux at ENSO time scales in the subthermocline of the Southeastern Pacific

The question of how energy is redistributed in the ocean has renewed the interest for the processes leading to midlatitude subthermocline variability at low frequency. Here we investigate a process that has been disregarded although potentially relevant for climatic studies dealing with the planetary energy budget. The focus is on the Southeastern Pacific where an efficient oceanic teleconnection takes place, linking the remote surface equatorial momentum forcing with the subthermocline through the vertical propagation of low-frequency long-wavelength extratropical Rossby waves (ETRW). A high-resolution model is used to document the vertical energy flux associated with ETRW at interannual to decadal time scales. The analysis of a long-term (1958-2008) simulation reveals that the vertical energy flux can be interpreted to a large extent as resulting from the coastally forced ETRW as far south as 35 degrees S, so that heat content variability can be predicted along theoretical trajectories originating from the coast below the thermocline. It is shown that the vertical energy flux associated with the El Nino Southern Oscillation forms beams below the thermocline that account for a large fraction of the total vertical energy flux at interannual time scales. Extreme El Nino events are the dominant contributor to this flux, which is hardly impacted by mesoscale activity. The energy beams experience a dissipation processes in the ocean below 1000 m that is interpreted as resulting from vertical turbulent diffusion. Our results suggest that the ETRW at ENSO time scales are strongly dissipated at the surface but still can modulate the heat content in the deep ocean of the Southeastern Pacific