A Coupled Atmosphere-Ocean Model for Transient Climate
Change Studies
Gary L. Russell, James R. Miller, and David Rind
1995: Atmosphere-Ocean, 33 (4), 683-730
Abstract
A new coupled atmosphere-ocean model has been developed for
climate predictions at decade to century time scales. The atmospheric
model is similar to that of Hansen et al. [1983] except that the
atmospheric dynamic equations for mass and momentum are solved using
Arakawa and Lamb's [1977] C grid scheme, and the advection of potential
enthalpy and water vapor uses the linear upstream scheme [Russell and
Lerner, 1981]. The new global ocean model conserves mass, allows for
divergent flow, has a free surface and uses the linear upstream scheme
for the advection of potential enthalpy and salt. Both models run at
4° × 5° resolution, with 9 vertical layers for the atmosphere and 13
layers for the ocean. Twelve straits are included, allowing for
subgrid-scale water flow. Runoff from land is routed into appropriate
ocean basins. Atmospheric and oceanic surface fluxes are of opposite
sign and are applied synchronously. Flux adjustments are not used.
Except for partial strength alternating binomial filters [Shapiro,
1970] which are applied to the momentum components in the atmosphere
and oceans, there is no explicit horizontal diffusion.
A 120-year simulation of the coupled model starting from the
oceanic initial conditions of Levitus [1982] is discussed. The model
dynamics stabilize after several decades. The maximum northward ocean
heat flux is 1.4 × 10^15 W at 16°N. The model appears to maintain the
vertical gradients characterizing the separation between the upper and
deep ocean spheres. Inadequacies in the coupled model simulation lead
to decreasing temperature and salinity in the high latitude North
Atlantic and to a poor simulation of the northern North Atlantic
thermohaline circulation. The mass transport of the Gulf Stream is
about half of observed values, while the transports of the Kuroshio and
Antarctic Circumpolar Currents are similar to observations. Additional
deficiencies include a climate drift in the surface air temperature of
0.006°C/year due to a radiation imbalance of 7.4 W/m² at the top of the
atmosphere, and too warm temperatures in the eastern portions of
tropical oceans. The coupled model should be useful for delineating
modeling capabilities without the use of flux adjustments, and should
serve as a benchmark for future model improvements.
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