Short description of TropFlux

The TropFlux project aims at providing daily, timely, accurate air-sea heat and momentum flux data for the entire 30°N-30°S region. Wind stresses and the four components of net surface heat flux are currently available for the entire 1979 to July 2012 period. We are currently working on a regular (~monthly) update of the TropFlux product until 3-4 months behind realtime, which should be available in 2013.

TropFlux is largely derived from a combination of ERA-I re-analysis data for turbulent and longwave fluxes, and ISCCP surface radiation data for shortwave flux. All input products are bias- and amplitude-corrected on the basis of Global Tropical Moored Buoy Array data, before surface net heat flux and wind stresses are computed using the COARE v3 bulk algorithm. A precise description of the flux computation procedure, as well as a detailed evaluation against other timely, daily air-sea heat flux alternatives (OAFLUX, NCEP, NCEP2, ERA-I) is provided in Praveen Kumar et al. 2012. The wind stress product is described, evaluated and compared against other widely used products (QuikSCAT, NCEP, NCEP2, ERA-I) in Praveen Kumar et al. 2013

We believe that this product offers the following advantages:

• better variability and less biases than re-analysis fluxes (and equivalent or slightly better than the best performing products: OAFLUX for heat fluxes and ERA-I for wind stresses) ,
• available until July 2012, and soon updated every month, lagging realtime by ~3 months,
• a simple estimate of surface shortwave radiation is provided from OLR data, as a near-realtime alternative to the more accurate but irregularly updated ISCCP data.

The TropFlux product has been developed under a collaboration between the Laboratoire d'Océanographie: Expérimentation et Approches Numériques (LOCEAN) from Institut Pierre Simon Laplace, France and National Institute of Oceanography/CSIR, India. Bilateral scientific visits to France and India have been supported by Institut de Recherche pour le Développement, France.

Data format

The following variables are provided:

• surface net short wave radiation (swr, W/m^2, positive downward)
• surface net longwave radiation (lwr, W/m^2, positive downward)
• latent heat flux (lhf, W/m^2, positive downward)
• sensible heat flux (shf, W/m^2, positive downward)
• net air-sea flux (netflux, W/m^2, positive downward)
• zonal wind stress (taux, N/m^2, positive eastward)
• meridional wind stress (tauy, N/m^2, positive northward)
• wind stress module (tau, N/m^2, positive)
• wind module at 10m height (ws, m/s, positive)
• Specific humidity at 2m height (q2m, g/kg, positive)
• Air temperature at 2m height (t2m, degC)
• Bulk sea surface temperature (sst, degC)

The data is provided in NetCDF format, with one file per variable for the complete dataset. Daily (almost 1Gb per file) and monthly (32Mb per file) average data are proposed. The data is provided on a 1° resolution grid (with the same land-sea mask than for the OAFLUX project, http://oaflux.whoi.edu/ ). There are 60 points in latitude at -29.5, -28.5, ..., 28.5 (positive north of the equator). There are 350 points in longitude at 30.5, 31.5, ..., 379.5 (eastward of the Greenwich meridian). This choice on longitude has been made: to avoid including points with only land (in central Africa)and to avoid cutting through a tropical ocean.

References

Praveen Kumar, B., J. Vialard, M. Lengaigne, V. S. N. Murty, M. J. McPhaden, 2012: TropFlux: Air-Sea Fluxes for the Global Tropical Oceans - Description and evaluation, Climate Dynamics, 38, 1521-1543, doi:10.1007/s00382-011-1115-0

Praveen Kumar, B., J. Vialard, M. Lengaigne, V. S. N. Murty, M. J. McPhaden, M.F. Cronin and F. Pinsard and K. Gopala Reddy, 2013: TropFlux wind stresses over the tropical oceans: evaluation and comparison with other products, Climate Dynamics, 40(7-8), 2049-2071, doi:10.1007/s00382-012-1455-4