Dynamic Response of the Ocean to Global Warming

Scott Power, Bureau of Meteorology Research Centre
GPO Box 1289K, Melbourne, VIC 3001, AUSTRALIA
s.power@bom.gov.au, Phone: +613 9669 4578, Fax: +613 9669 4660 

Background/Objectives

Ocean temperature is expected to change in response to global warming. Part of this results from the direct uptake of anomalous surface heat. This heat, together with changes in the wind-stress and freshwater fluxes can also alter ocean currents and mixing rates, and this too can effect the way heat is distributed within the ocean. We might call this latter effect the "dynamic" response to global warming. The purpose of this sub-project is to estimate the magnitude of this dynamic effect over the first 80 years of transient CO2 experiments in coupled GCMs. We also wish to determine the relative importance of the dynamic response, how it arises, where it is large and which particular fluxes are most important in driving it. Recent work suggests that the dynamic effect acts to boost the surface response on these time-scales by over 30% (Power 1998). This is based on the results obtained from one particular model only (Power et al. 1993, Colman et al. 1995) and so it is worth testing the conclusions drawn in a variety of other models, especially in the models which exhibit less climate drift.

Method

The method used will be similar to that described by Power (1998) and is similar in philosophy to that described by Power and Hirst (1997). We will use the surface fluxes from the CGCMs (both control and perturbed values) to drive an ocean model and a hybrid coupled model (Power et al. 1995). The heat will be used to drive the temperature equation and a passive tracer equation, in order to estimate the dynamic response to heating.

Fields Required

The following 4x20 year mean fields are required from both the control and perturbed integrations:
  1. wind-stress (zonal and meridional)
  2. total heat flux
  3. total freshwater flux
  4. 3-D ocean T and S
  5. sea-ice thickness and concentration
  6. overturning in various basins

References

Colman et al. 1995: A non-flux corrected transient CO2 experiment using the BMRC coupled atmopshere/ocean GCM. Geophys. Res. Lett., 22, 3047-3050.

Power et al. 1993: The BMRC coupled atmosphere/ocean/sea-ice model. BMRC Res. Rep.

Power, SB, 1998: On the dynamic response of the ocean to global warming. J. Phys. Oceanogr. (submitted).

Power, SB, and AC Hirst, 1997: Eddy parameterization and the oceanic response to idealized global warming. Climate Dyn., 13, 417-428.

Power, SB, et al. 1995: Stochastic variability at the air-sea interface on decadal time-scales. Geophys. Res. Lett., 22, 2593-2596.

Other relevant publications by the PI:

Power 1995: Climate drift in a global OGCM. J. Phys. Oceanogr., 25, 1025-1036.

Power and R. Kleeman, 1993: Multiple equilibria in a global OGCM. J. Phys. Oceanogr., 23, 1670-1681.

Power et al., 1994: On the stability of the NADWF in a global OGCM. J. Phys. Oceanogr., 24, 904-916.

Power et al. 1995: Modeling the atmospheric response to long-lived SST anomalies in the North Atlantic. J. Climate, 8, 2161-2180.

Power and Kleeman, 1994: Surface heat flux parameterization and the response of OGCMs to high latitude freshening. Tellus, 46A, 86-95.

Kleeman and Power, 1995: A simple atmospheric model of surface heat flux for use in ocean modeling studies. J. Phys. Oceanogr., 25, 92-105.