Model CCSR: Elaborations

Participation

Spinup/Initialization

• First stage: The model atmosphere is integrated for 20 years starting from the initial conditions for the AMIP experiment.  The last 15 years of this simulation is used for ocean spinup as described in the third stage below.

• Second stage: The ocean model is integrated for 2000 years with acceleration from static, isothermal, isohaline initial conditions.  The ocean surface conditions are restored to climatology--Levitus (1982) SST and SSS and Hellerman and Rosenstein (1983) wind stress.

• Third stage: The ocean model is integrated for 4000 years with the atmospheric fluxes obtained in the first-stage spinup. The ocean surface conditions are restored to the same climatology as in the second-stage spinup, except that the SST are modified for the last 2000 years, according to the AMIP data.  Initial flux-adjustment terms for heat and salinity are obtained.

• Fourth stage:  The atmosphere and ocean models are coupled, and the system is integrated for 40 years, with the surface conditions restored to climatology as in the third stage.  Additional flux-adjustment terms are obtained for heat and salinity.
• Fifth stage:  The coupled model is run for 80 years with the flux adjustment terms for heat and salinity obtained above.  The last 40 years of this run constitutes the CMIP data set.

Land Surface Processes

• The skin temperature of soil and land ice is predicted by a heat diffusion equation that is discretized in 3 layers with a zero-flux lower boundary condition; heat capacity and conductivity are spatially uniform values. Surface snow is treated as part of the uppermost soil layer, and thus modifies its heat content, as well as the heat conduction to lower layers.

• Soil liquid moisture is predicted in a single layer according to the "bucket" formulation of Manabe et al. (1965) The moisture field capacity is a spatially uniform 0.15 m, with surface runoff occurring if the predicted soil moisture exceeds this value. Snowmelt contributes to soil moisture, but if snow covers a grid box completely, the permeability of the soil to falling liquid precipitation becomes zero. For partial snow cover, the permeability decreases proportional to increasing snow fraction.

• Soil moisture is depleted by surface evaporation; the evaporation efficiency beta is not determined solely by the ratio of soil moisture to its saturation value, but is limited by the specified stomatal resistance of the vegetation. Other effects of vegetation, such as the interception of precipitation by the canopy and its subsequent reevaporation, are not included.

• Continental runoff is returned to the oceans, by means of a river transport model (cf. Miller et al. 1994). Runoff instantaneously increases the river and lake mass of a grid box, which is also affected by the local balance of precipitation and evaporation. For each continental grid box, a river direction file indicates the downstream routing to one of the 8 neighboring grid boxes. The river mass flux out of a grid box is computed as a function of the river and lake mass that lies above the local sill depth, an effective flow speed that depends on the local orography gradient, and the mean distance to the downstream neighbor. The flow speed is prescribed as a constant 0.3 m sec^-1.

Sea Ice

References

Levitus, S., 1982: Climatological atlas of the world's oceans. NOAA Professional Paper 13, 173 pp.

Manabe, S., J. Smagorinsky, and R.F. Strickler, 1965: Simulated climatology of a general circulation model with a hydrologic cycle. Mon. Wea. Rev., 93, 769-798.

Miller, J.R., G.L. Russell, and G. Caliri, 1994: Continental scale river flow in climate models. J. Climate, 7, 914-928.

Semtner, A.J., 1976: A model for the thermodynamic growth of sea ice in numerical investigations of climate.  J. Phys. Oceanogr., 6, 379-389.
 

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CMIP Documentation Directory

Last update 15 May, 2002.  This page is maintained by Tom Phillips (phillips@pcmdi.llnl.gov).
 

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