Picture: Breaking wave. Credit: Matt Hardy (Unsplash)

Our climate records suffer from large uncertainties in surface heat budget over the Southern Ocean. To better understand the biases and ultimately improve the quality of our climate records, CLEX researches and their collaborators undertook in situ measurements using the NOAA Physical Sciences Division flux system during the Clouds, Aerosols, Precipitation, Radiation, and Atmospheric Composition over the Southern Ocean (CAPRICORN) experiment in 2016.  

The researchers compared the surface heat fluxes calculated from the in situ data using the COARE 3.5 bulk algorithm against estimates from a range of products including the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) product, the Australian Integrated Marine Observing System (IMOS) routine observations, and the Objectively Analyzed Air–Sea Heat Fluxes (OAFlux) project hybrid dataset.

The ERA-Interim and OAFlux data were further compared with the Southern Ocean Flux Station (SOFS) air–sea flux moored surface float deployed for a year.

The results show the ERA-Interim and OAFlux estimate sensible heat flux Hs accurately to within ±5Wm-2 and latent heat flux Hl to within ±10 W m-2.

ERA-Interim gives a positive bias in Hs at low latitudes and in Hl at high latitudes, and OAFlux displays consistently positive bias in Hl at all latitudes.

No systematic bias with respect to wind or rain conditions was observed. Although some differences in the bulk flux algorithms were noted, these biases can be largely attributed to the uncertainties in the observations used to derive the flux products.

Paper: Bharti, V., E. Schulz, C. W. Fairall, B. W. Blomquist, Y. Huang, and A. Protat, S. T. Siems, M. J. Manton, 2019: Assessing surface heat flux products with in situ observations over the Australian sector of the Southern Ocean.  Journal of Atmospheric and Oceanic Technology36. 2019.