Surface wind response to oceanic fronts

Qingtao Song, University of Rhode Island

Abstract

The surface wind response in mesoscale to oceanic front was analyzed by using a combination of scatterometer (NSCAT and QuikSCAT) wind data and Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature (SST) data in conjunction with numerical simulations made with Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5). ^ MM5 simulations of the response of the marine atmospheric boundary layer (MABL) to a sharp SST front are compared with observations made during the Frontal Air-Sea Interaction Experiment (FASINEX) in the North Atlantic. The fully three-dimensional (3D) MM5 with the Medium-Range Forecast (MRF) boundary-layer model captures the appropriate boundary-layer physics at the mesoscale for moderate wind speeds quite well as indicated by the good agreement in observed and modeled properties for Frontal Air-Sea Interaction Experiment (FASINEX). ^ Scatterometer wind data are then combined with Gulf Stream north wall positions digitized from SST fields. Each scatterometer pass was paired with the Gulf Stream path closest in time. All match-ups were then visually examined and only those for which the Gulf Stream presented a reasonably straight segment over which the wind field was free of atmospheric fronts or large curvature were selected. Ten match-ups met these criteria for the period studied. ^ The response of the scatterometer wind field to the SST/current front was analyzed in detail for these ten cases using MM5. The importance of pressure gradients induced by changes in air temperature, moisture, and vertical mixing across oceanic front is studied in the momentum budget analysis. Our findings suggest that the perturbation pressure resulting from the thermal forcing by the front accounts for the decrease in wind speed when moving from warm to cold water and the increase observed in the converse. The dynamical forcing associated with strong surface currents is also shown to modify scatterometer-derived winds. Finally the numerical simulations suggest that the dynamical and thermal effects are very nearly additive. ^

Subject Area

Physical Oceanography|Atmospheric Sciences

Recommended Citation

Qingtao Song, "Surface wind response to oceanic fronts" (2006). Dissertations and Master's Theses (Campus Access). Paper AAI3225330.
http://digitalcommons.uri.edu/dissertations/AAI3225330

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