Recorded presentation4B.1
Synoptic scale changes in surface heat fluxes due to wind waves
Mark A. Bourassa, COAPS/Florida State Univ., Tallahassee, FL
Surface turbulent stress in the tropical oceans has been shown (Kara et al. 2007) to be modified by swell (surface water waves generated by distant storms). For the published example for 0Z on January 1, 2005, the change in wind shear (U10 – Usfc) was modified by from -15% to +10%, and the monthly average was changed by from -10% to +5%. However, the focus of that study was the change in wind shear and the drag coefficient. Herein, the change in surface turbulent heat fluxes will be examined. Heat fluxes are dependent on the scalar wind speed rather than the vector wind speed; therefore, longer term averaged are likely to be more impacted by wave-related changes in the magnitude of the shear. These waves are typically driven by synoptic scale winds, and the resulting wave trains modify fluxes over a large portion of the ocean basin. Preliminary results for the tropical Pacific show wave-induced biases in the scalar wind speed: roughly -12% in the western equatorial Pacific Ocean, and roughly +8% in the eastern Pacific Ocean. The impact of waves on biases in surface turbulent heat fluxes will be discussed. In the tropical Pacific Ocean, the surface heat flux is overestimated in the West and underestimated in the East. In contrast, the surface wind shear in the Southern Ocean is on averaged deceased, resulting in reduced surface heat fluxes. In regions along shorelines and SST fronts, the changes in atmospheric characteristics (temperature and humidity) are well correlated with changes in wind. These changes must also be considered when investigating wave-related biases. The importance of these considerations will be shown to vary regionally and seasonally.
Session 4B, Basin-Scale Forcing of Synoptic Weather Patterns
Tuesday, 13 January 2009, 8:30 AM-9:45 AM, Room 128B
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