Air-sea exchange processes

Bradley, E.F. Dr; Telephone (02) 6246 5575; Facsimile: (02) 6246 5560; frank.bradley@cbr.clw.csiro.au

Research organisation: CSIRO Land and Water, GPO Box 821, Canberra ACT 2601

Collaborators: CSIRO, Divisions of Oceanography and Atmospheric Research; Flinders Institute of Atmospheric and Marine Science, NOAA Environmental Technology Laboratory, Woods Hole Oceanographic Institution, Oregon State University, University of Hawaii.

Objectives:

Through participation, aboard R/V Franklin, in the international TOGA Coupled Ocean-Atmosphere Response Experiment (COARE) to the western Pacific warm pool, to:

• study turbulent and radiative heat exchange in the tropical oceans surrounding Australia,
• attempt closure of heat and freshwater budgets in the tropical oceans,
• develop an improved model to obtain air-sea fluxes using bulk methods,
• participate in coordination and validation of all COARE surface datasets.

Methodology:

The TOGA-COARE Intensive Observing Period was conducted in the western Pacific warm pool from November 1992 to February 1993, involving 15 ships, 7 aircraft and many fixed moorings, from several nations. R/V Franklin participated with two month-long cruises, co-ordinated with the other ships and aircraft to provide comprehensive and continuous measurements of atmospheric and oceanic physical variables during this period. Particular attention was paid to the accuracy of measurement, in order to achieve the COARE goal of 10 W/m2 for net air-sea heat exchange, as needed to validate the performance of improved coupled GCMs. Problems specific to the warm pool environment are a strongly convective atmosphere, light winds, and strong sensitivity of atmospheric response to small SST variations. The latter are themselves complicated by the effects of strong solar heating and high rainfall, affecting density stratification of the upper ocean.

Progress:

The two COARE cruises were undertaken successfully, and a large volume of high-quality atmospheric and oceanic data obtained; this has been added to international archives of COARE data. Some results have been published, but there remains the potential for further analysis toward the understanding of tropical climate processes. Maximum benefit flowed to individual participants in COARE through close collaboration during the post-experiment data analysis phase. The project was extended beyond the previously estimated date, through the appointment of Dr Bradley as co-chair of the COARE Air-Sea Interaction Working Group, convened to coordinate all surface meteorology and air-sea flux observations, and co-chair of the committee organising an international COARE review conference in Boulder, Colorado, 7-14 July 1998. The Proceedings of this conference will be published by WCRP as a monograph of COARE scientific results to date. Other outcomes are:

• observation and physical description of the diurnal warming and flux-generated cool skin of the upper ocean,
• development of a bulk flux algorithm for tropical oceans, taking account of convective conditions, light winds and the sensible heat contributed to the ocean by rainfall; it also includes models for the diurnal warming and cool skin, to obtain true skin temperature (this algorithm is being increasingly used in other regions and applications, e.g satellite estimation of surface stress and heat fluxes),
• correction of the standard equation used to compute downwelling longwave radiative flux from pyrgeometers,
• evaluation of the errors in rainfall measurement by optical and funnel gauges aboard ship, and recommendations for their use in obtaining ground truth for remote sensing of rainfall over the ocean.

The COARE project has benefited subsequent tropical air-sea interaction studies. A finding that the contributions of vertical and horizontal advection to the ocean heat and freshwater budgets were unexpectedly large, led to changes in methodology, resulting in successful closure of those budgets in the Indian ocean warm pool. Work in the Indian ocean is continuing.

Period: starting date 1991-07; completion date 1995-07

Status: completed

Keywords: COARE, climate, air-sea fluxes, radiation, rainfall, SST

Publications:

Bradley, E.F and Lukas, R.B. (editors) (1999). Proceedings of the TOGA-COARE International Conference - COARE98 (Boulder, Colorado, USA, 7-14 July 1998), WCRP, Geneva, Switzerland.

Bradley, E.F. and Weller, R.A. (1995). Joint Workshop of the TOGA COARE Flux and Atmospheric Working Groups. Boulder, Colorado, USA, 11-13 July 1995, TOGA COARE International Project Office, University Corporation for Atmospheric Research, Boulder, USA, 35pp.

Bradley, E.F. and Weller, R.A. (1995). Third Workshop of the TOGA COARE Air-Sea Interaction (Flux) Working Group. University of Hawaii, Honolulu, USA, 2-4 August 1995, TOGA COARE International Project Office, University Corporation for Atmospheric Research, Boulder, USA, 34pp.

Bradley, E.F. and Weller, R.A. (1997). Fourth Workshop of the TOGA COARE Air-Sea Interaction (Flux) Working Group. Woods Hole Oceanographic Institution, Mass., USA, 9-11 October 1996, TOGA COARE International Project Office, University Corporation for Atmospheric Research, Boulder, USA, 61pp.

Bradley, E F, Moncrieff, M. and Weller, R.A. (1997). Joint Workshop of the TOGA COARE Air-Sea Interaction (Flux) and Oceans Working Groups, and GEWEX GCSS-WG4. NCAR, Boulder, USA, 16-19 May 1997, TOGA COARE International Project Office, University Corporation for Atmospheric Research, Boulder, USA.

Bradley, E.F., Godfrey, J.S., Coppin, P.A. and Butt, J.A. (1993). Observations of net heat flux into the surface mixed layer of the western equatorial Pacific Ocean. Journal of Geophysical Research 98, 22521-22532.

Burns, S.P., Khelif, D., Friehe, C.A., Williams, A.G., Hignett, P., Grant, A.L.M., Hacker, J.M., Rogers, D.P., Bradley, E.F., Weller, R.A., Cronin, M.F., Anderson, S.P., Fairall, C.W. and Paulson, C.A. (submitted). Comparisons of aircraft, ship, and buoy meteorological measurements from TOGA COARE. Journal of Geophysical Research.

Chinman, R., Bradley, E.F., Busalacchi, A., Eriksen, C., Godfrey, J.S., Guzler, D., Hacker, P., Hu, D., Johnson, R., Lukas, R., Marks, F., Nakazawa, T., Redelperger, J-L., Takeuchi, K., Weller, R.A. (1995). Summary report of the TOGA-COARE International Data Workshop. Toulouse, France, 2-11 August 1994. (TOGA COARE International Project Office, University Corporation for Atmospheric Research, Boulder, USA)

Donlon, C.J., Keogh, S.J., Baldwin, D.J., Robinson, I.S., Ridley, I., Sheasby, T., Barton, I., Bradley, E.F., Nightingale, T. and Emery, W. (1998). Solid state radiometer measurements of sea surface skin temperature. Journal of Atmospheric and Oceanic Technology 15, 775-787.

Fairall, C.W., Bradley, E.F., Rogers, D.P., Edson, J.B., and Young, G.S. (1996). Bulk parameterization of air-sea fluxes for Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Response Experiment. Journal of Geophysical Research 101, 3747-3764.

Fairall, C.W., Persson, P.O.G., Bradley, E.F., Payne, R.E. and Anderson S.P. (1998). A new look at calibration and use of Eppley Precision Infrared Radiometers. Part 1: Theory and application. Journal of Atmospheric and Oceanic Technology 15, 1230-1243.

Fairall, C.W., Bradley, E.F., Godfrey, J.S., Wick, G.A., Edson, J.B., and Young, G.S. (1996). Cool-skin and warm-layer effects on sea surface temperature. Journal of Geophysical Research 101, 1295-1308.

Godfrey, J.S., Bradley, E.F., Coppin, P.A., Pender, L., McDougall, T.J., Schulz, E.W., and Helmond, I. (1999). Measurements of upper ocean heat and freshwater budgets near a drifting buoy in the equatorial Indian ocean. Journal of Geophysical Research (in press).

Grachev, A.A., Fairall, C.W. and Bradley, E.F. (1999). Convective profile constants revisited. Boundary-Layer Meteorology (submitted).