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Climate Variability & Change

We propose to investigate seasonal and spatial variability of the coupling between surface winds and sea surface temperature (SST) over mid-latitudes on spatial scales of O(100-1000 km), in what is loosely considered the oceanic mesoscale. Over these spatial scales, QuikSCAT wind stress and microwave SST fields show that surface winds are stronger over warm SST and weaker over cool SST. These SST-induced wind stress perturbations vary seasonally by a factor of two to five in accordance with the ambient large-scale wind speed; calm summertime winds dramatically mute the SST-induced mesoscale wind stress field, leading to a seasonal pulsing of the stress perturbations over mid- latitudes observed very clearly in scatterometer wind stress fields. Despite the large amplitude of this seasonal stress pulsing, its impacts on ocean circulation, ocean dynamics, and dynamical structure of the atmospheric boundary layer are largely unknown and will form the primary basis of our proposed research. Our specific objectives are threefold: 1) Analyze the atmospheric and oceanic consequences of the seasonal pulsing of the SST-induced mesoscale wind stress field over mid-latitudes and identify the dynamical mechanisms governing the atmospheric and oceanic responses. 2) Investigate geographical variations of the mesoscale wind-SST coupling and governing dynamical mechanisms. 3) Investigate the spatial and temporal scales in which the wind-SST coupling changes from a positive correlation in which the ocean forces an atmospheric response to a negative correlation in which the atmosphere drives an oceanic response. To meet these goals, we will supplement analysis of satellite-derived measurements of QuikSCAT scatterometer surface winds, microwave SST, and merged sea surface height (SSH) with high-resolution numerical simulations of the atmosphere and ocean using the U.S. Navy’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) model. Feedback effects onto the ocean will be investigated observationally using wind stress, SSH, and SST and compared with mechanisms proposed from ocean modeling and analytical studies. Dynamical consequences of the seasonal wind stress pulsing will be investigated from COAMPS atmospheric and oceanic simulations in both coupled and uncoupled modes over select mid-latitude oceanic frontal regions, whose topics will include: mass and heat transports and baroclinic structure of the major western boundary currents, eddy kinetic energy, Ekman upwelling perturbations, eddy propagation and structure, Rossby wave propagation and the seasonally- and geographically-varying momentum budget in the atmospheric and oceanic boundary layers. Findings from the model simulations will be used to gain insight into seasonal and geographical variability observed from satellite. Finally, we will use satellite wind and SST observations to investigate the dependence of the wind-SST coupling on spatial scale to determine the length scales at which the positive correlation between surface winds and SST becomes negative. The proposed research addresses the NASA strategic objective of conducting a program of research to advance Earth observation from space and to improve scientific understanding of the coupled climate system through interdisciplinary ocean-atmosphere research. It contributes to the particular OVWST-ROSES focus areas by utilizing multi-year QuikSCAT scatterometer wind observations for oceanographic, meteorological, and climate research. Furthermore, we anticipate that rigorous comparisons between the satellite observations and the COAMPS simulations will lead to improvements in the simulation of mesoscale ocean-atmosphere coupling in operational COAMPS forecasts in support of the NASA-ROSES strategic objective to "improve the impact and effectiveness of scatterometer and related ocean surface vector wind measurements for operational uses" through improvements in short-term climate forecasting.

Project PI: Tracy Haack/Naval Research Laboratory

Naval Research Laboratory Marine Meteorology Division Monterey, CA 93943-5502

Email: haack@nrlmry.navy.mil

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Started: Sep 29, 2010

Last Activity: Mar 16, 2011

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