AMIP II Diagnostic Subproject 5
Ocean surface fluxes of heat, momentum, buoyancy and their implied transports
Short title: Ocean surface fluxes
Peter J. Gleckler and Karl E. Taylor
Program for Climate Model Diagnosis and Intercomparison
Simulations made with coupled ocean-atmosphere models frequently "drift" away from the observed climate. The situation has improved in recent years (e.g., Boville et al., 1997), but the tuning required to minimize this drift remains a sensitive and unfortunate necessity. Identifying and understanding biases in the simulated air-sea exchange of heat, momentum and buoyancy is an important step towards resolving the climate drift in coupled ocean-atmosphere models. AMIP offers the opportunity to examine in detail surface fluxes simulated with AGCMs constrained by realistic sea surface temperatures (SST) and sea-ice conditions. This serves as a useful test to examine the readiness of an AGCM to be successfully (minimal drift) coupled to an OGCM.
For many of the AMIP I simulations the implied ocean heat transport in the Southern Hemisphere was equatorward. These unrealistic transports resulted from deficiencies in the simulated cloud-radiative effects (Gleckler et al., 1995). Additionally, systematic biases in the simulated surface heat fluxes were identified by direct comparison with observationally-based estimates (Randall and Gleckler, 1996 and Gleckler and Weare, 1997).
Simulated ocean surface fluxes and their implied meridional transports
need to be studied in further detail. The continuing primary objective
of this subproject is to identify and explain systematic errors by making
use of the best available observations. The emphasis on seasonal
climatologies (and not interannual variability) reflects that: 1) despite
prescribed SSTs, AGCMs do not yet adequetly simulate the seasonal cycle
of surface heat fluxes (Randall and Gleckler, 1996), and 2) observations
are sparse, and consequently it is believed that available composite climatologies
are more credible than estimates of interannual variability. However, several
recent satellite products show promise in capturing interannual variability
during part of the AMIP II period, and may deserve consideration for comparison
with the simulations. Regional field studies (e.g., TOGA-COARE intensive
flux array) may also prove useful. The proposed research consists
of the following:
- Evaluation of simulated global ocean seasonal climatologies of a) all terms of the surface energy balance b) surface wind stress c) buoyancy (freshwater flux)
- Evaluation of the annual mean implied meridional transports of heat, momentum and density in the Atlantic, Indian, Pacific and global oceans
- Attempt to identify the reasons for existing surface flux and transport biases (e.g., Gleckler et al., 1995).
Monthly mean model output needed:
- all surface and TOA radiative fluxes
- surface latent and sensible heat fluxes
- surface eastward and northward wind stress
- evaporation and precipitation
- cloud cover, surface wind speed (10m) and surface air temperature (2m)
Because of the large uncertainties associated with "state-of-the-art" observational estimates, it is likely that many of them will continue to be compared with models. Randall and Gleckler (1996) found that despite the large differences between the observational estimates, collectively they have helped to identify several important model biases. Thus it is expected that a diverse collection of observations will be used to study the AMIP simulations, including a variety of surface and satellite based estimates, reanalysis, and field studies.
da Silva, A.M., and S. Levitus, 1995: Atlas of Marine Surface Data, Vol. 2, U.S. Government Printing Office. DC.
Gleckler, P. J., D. Randall, G. Boer, R. Colman, M. Dix, V. Galin, M. Helfand, J. Kiehl, A. Kitoh, W. Lau, X. -Z. Liang, V. Lykossov, B. McAvaney, K. Miyakoda, S. Planton, and W. Stern, 1995: Cloud-radiative effects on implied oceanic energy transports as simulated by atmospheric general circulation models, Geophysical Research Letters, 22, 791-794
Gleckler, P. J. and Bryan C. Weare, 1997: Uncertainties in global ocean surface heat flux climatologies derived from ship observations. Journal of Climate (in press).
Randall, D.A., and P.J. Gleckler, 1996: Systematic biases in AGCM ocean surface heat fluxes. WCRP Workshop on air-sea flux fields for forcing ocean models and validating GCMS, WCRP-95, WMO/TD-No. 762.
For further information, contact the AMIP Project Office (email@example.com).
Last update: 18 June 1999. This page is maintained by firstname.lastname@example.org