Ocean-atmosphere energy exchange along mid-latitude SST fronts

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Tuesday, 6 January 2015: 2:45 PM
224A (Phoenix Convention Center - West and North Buildings)
Larry W. O'Neill, Oregon State Univ., Corvallis, OR; and T. Haack

Sea surface temperature (SST) frontal zones are areas of strong energy exchange between the ocean and atmosphere. Here, we investigate the pathways of energy transfer between the ocean and atmosphere at the oceanic mesoscale using satellite and buoy observations and numerical simulations. Mesoscale variations in SST associated with meanders in SST fronts, eddy-like features, and singular sharp fronts cause large spatial perturbations in the surface sensible, latent, and radiative heat fluxes. Over warm SST perturbations, sensible and net radiative heat flux perturbations are generally around 10-20 W m-2 per degC SST, while latent heat flux perturbations can exceed 40 W m-2 per degC SST. The net heating at the surface of the atmospheric boundary layer causes an adjustment of the lower atmosphere mass and turbulence fields, which culminates in larger surface wind stresses over warm SST and weaker stresses over cool SST. From an energy perspective, the atmosphere thus converts oceanic thermal and radiative energy into oceanic mechanical energy via the mesoscale surface wind stress response to SST driven by the SST-induced surface heat and radiative flux responses. The conversion process, however, is quite inefficient: only roughly O(1%) of the thermal and radiative energy input into the base of the atmosphere from SST-induced surface heating perturbations is returned to the ocean locally via mechanical energy input from the SST-induced surface wind stress perturbations. We investigate the fate of the remaining energy input into the atmosphere from ocean-atmosphere interactions associated with mesoscale SST perturbations. Using numerical simulations from the COAMPS mesoscale prediction system, we find that, in these simulations, energy is redistributed vertically and horizontally through transport by the large-scale wind. SST perturbations also generate significant anomalies in total potential energy of the atmosphere. Because of these energy transport and potential energy production perturbations, energy flow between the atmosphere and ocean is not generally local but can involve influences from the large-scale distribution of the mesoscale SST field. Finally, the largest terms in the energy budget are associated with the latent heat input into the atmosphere. Preliminary results suggest that the largest rectification effect of mesoscale SST perturbations on the atmosphere occurs through water vapor transport and phase transitions. Potential implications of these energy flow processes on the large-scale state of the atmosphere and ocean circulation will also be discussed.