Quantifying the Mesoscale Rectification of Latent Heat Flux
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2022
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University of Hawaii at Manoa
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Abstract
Ocean mesoscale fronts and eddies can impact large scale features due to nonlinear rectification. This project quantifies the rectification of ocean mesoscale sea surface temperature, wind speed, and specific humidity to the large-scale latent heat flux. We quantified nonlinearities caused by (1) the Clausius Clapeyron relation, (2) the positive correlation of sea surface temperatures and wind speed at the mesoscale, and (3) the covariability of wind speed and specific humidity. A Taylor Expansion to the second order of the latent heat flux around the large-scale wind speed, sea surface temperature, and specific humidity is used to estimate the nonlinear rectification of the three nonlinearities for the Gulf Stream, Kuroshio Extension, and Agulhas Return Current. We conducted two trials. Trial 1 utilized satellite observations of wind speed, sea surface temperature, and an estimated specific humidity to calculate nonlinearity (1) and (2). Trial 2 utilized ERA5 reanalysis of wind speed, sea surface temperature, and specific humidity to calculate all three nonlinearities. The average of the rectification terms are small for each trial, and generally range from -0.5 to 1.8 W/m^2 with some regional exceptions. Results indicate that in Trial 1, the rectification from Clausius Clapeyron ranges from 0.09 to 3.85 W/m^2 and the rectification from the sea surface temperature-wind covariability ranges from -4.06 to 4.39 W/m^2 depending on the region. In Trial 2, the rectification from Clausius Clapeyron ranges from 0.05 to 3.74 W/m^2, the sea surface temperature-wind covariability ranges from -14.92 to 14.19 W/m^2, and the wind-specific humidity covariability ranges from -9.30 to 7.91 W/m^2. Results find that the Clausius Clapeyron term exhibits a dependence on background wind speed and both covariability terms exhibit a dependence on wind direction. All rectification terms exhibit a strong dependence on filter size and humidity. The Taylor Expansion in Trial 1 had a low error, however, the results from Trial 2 were highly variable and exhibited a large error that is directly related to the Clausius Clapeyron term. On large spatial and temporal averages, the rectification is modest but can be important at times over strong mesoscale sea surface temperature variance and under particular background wind conditions.
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Ocean temperature--Mathematical models, Ocean-atmosphere interaction--Mathematical models, Heat flux, Mesometeorology
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