Scale and Rossby number dependences of observed wind responses to ocean-mesoscale sea surface temperatures

Niklas Schneider, University of Hawai’i at Mānoa, International Pacific Research Center, Honolulu, United States
The horizontal-scale dependences of in-phase and lagged imprints of ocean-mesoscale sea surface temperatures on surface winds are investigated using daily AMSR-E radiometer and QuikSCAT scatterometer observations in the Southern Ocean. Spectral transfer functions separate underlying processes dependent on large-scale winds, horizontal wave-numbers and corresponding Rossby numbers. For Rossby numbers smaller than one, winds reflect modulations of the Ekman layer by sea surface temperature induced changes of hydrostatic pressure. Rossby numbers large compared to one suggest a balance of advection and modulations of vertical mixing. Corresponding impulse response functions reveal Doppler-shifted near-inertial lee waves excited by enhanced vertical mixing over warm sea surface temperature perturbations that interact with the downstream wake of warm air and low atmospheric pressure. Inertial turning of winds and hydrostatic pressure gradient forces strengthen the downwind convergence relative to the upwind divergence, and enhance the anticyclonic wind curl through near resonance on the right side of the wake. Time averaging smooths the response, and degrades the lee-wave.