Collaborative Research 

Atlantic Air-Sea fluxes from satellites, their variability and analysis of ocean models
Department of Atmospheric and Oceanic Science
University of Maryland, College Park

Understanding why oceanic heat flux estimates differ


Background
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An in depth comparison between the French Research Institute for Exploitation of the Sea (IFREMER)* heat flux estimates with those from Woods Hole Oceanographic Institution (WHOI)** was performed. One is based on satellite observations and the other one, on a combination of inputs from assimilation of remotely sensed, buoy and ship data, and numerical analyses. The study focuses on the Atlantic sector (70W-30E, 45S-45N) during 1996-2005 for daily, monthly, and annual time scales

The fluxes as well as the parameters that enter the bulk formulae are evaluated against buoy observations from the Prediction and Research Moored Array in the Atlantic (PIRATA; data as available at http://www.pmel.noaa.gov/pirata/); since WHOI uses PIRATA observations to adjust errors in its flux estimates, we also use independent data from three buoy experiments that are not used in assimilation by WHOI. These are:  FETCH (the "flux, etat de la mer, et teledetection en conditions de fetch variable"), the Baltic Sea Swell Experiment (BASE), and ROMEO, which was part of a field program off the North Carolina coast of the United States. It is shown that the differences in latent heat flux estimates are likely due to differences in specific humidity used in deriving these two products while those in sensible heat flux are likely due to differences in air temperature (Figure 1) (Santorelli et al., 2011).

 

Figure 1. Annual mean difference between the IFREMER and WHOI datasets during 1996-2005 for (a) sea surface temperature, (b) specific air humidity, (c) surface wind speed and (d) air temperature (units  are degrees Celsius for  sea surface and air temperature, gkg-1 for specific air humidity and ms-1 for surface wind speed).

Experiments were conducted with satellite based estimates of specific air humidity and air temperature (Jackson et al. (2006, 2009)) in the IFREMER approach based on the COARE3.0 algorithm. Resulting estimates of latent and sensible heat fluxes at two buoy locations from the PIRATA array (12N, 38W and 4N, 38W) are illustrated (Figures 2 and 3). This resulted in significant improvements in both sensible and latent heat estimates by the IFREMER method.

Figure 2  Comparison of the 12N, 38W PIRATA weekly-averaged (a) latent heat and (b) sensible heat flux to IFREMER_1, WHOI and IFREMER_2, IFREMER SST and 10m wind speed and Jackson et al. (2009). 10m specific air humidity and air temperature) estimates. The time span is 2/1/99-12/26/05; there were 107 values available or comparison. A table of statistics, including bias, RMSD and correlation coefficient is included (units are Wm-2)


Figure 3  Comparison of the 4N, 38W PIRATA weekly-averaged (a) latent heat and (b) sensible heat flux to IFREMER_1,WHOI and IFREMER_2 (IFREMER_1 SST and 10m wind speed and Jackson et al. 10m specific air humidity and air temperature) estimates. The time span is 2/15/99-12/26/05; there are 138 values available for comparison. A table of statistics, including bias, RMSD and correlation coefficient is included (units are Wm-2).

*http://cersat.ifremer.fr/layout/set/print/news/products_informations/new_release_of_satellite_turbulent_fluxes_1992_2007

 **http://oaflux.whoi.edu/heatflux.html

These two products were selected due to availability of daily values.

Note: IFREMER_1 denotes results from the original IFREMER approach; IFREMER_2 denotes results from IFREMER_1 when temperature and humidity are replaced with values from Jackson et al. (2009).

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Please send questions or comments to srb@atmos.umd.edu.
 Chuan Li cli-at-atmos.umd.edu
Last Modified on 2014-03-05