Model IAP/LASG1: Elaborations

Participation

Model IAP/LASG1 is an entry in the CMIP1 intercomparison only.

Spinup/Initialization

The procedure for spinup/initialization to the simulation starting point of the IAP/LASG coupled model for the CMIP intercomparison was as follows:

The atmospheric model (including soil moisture/temperature and snow cover/depth) was initialized from a previous simulation with prescribed SSTs (cf. Wu et al. 1996).

The oceanic model was spun up for 1700 years from an at-rest initial state with zonal-mean temperature and salinity specified from Levitus (1982). During the spinup, the model was forced by observed wind stresses after Hellerman and Rosenstein (1983), heat fluxes after Haney (1971) using observed atmospheric variables of Esbensen and Kushnir (1981), and Levitus (1982) observations of skin surface salinity (cf. Zhang et al. 1996, Yu 1997).

The atmospheric and oceanic models were coupled (cf. Zhang et al. 1992) and integrated for a total of 200 years using a monthly anomaly exchange scheme (cf. Liu et al. 1996 and Yu and Zhang 1997) that functions as a flux correction for heat and momentum. The ocean model's surface salinity also was restored to Levitus (1982) observations. Data from years 131 through 180 of the coupled simulation were supplied to CMIP I.

Land Surface Processes

Land surface processes are simulated following the Xue et al. (1991) modification of the SiB model of Sellers et al. (1986). Within the single-story vegetation canopy, evapotranspiration from dry leaves includes detailed modeling of stomatal and canopy resistances; direct evaporation from the wet canopy and from bare soil is also treated. Precipitation interception by the canopy is simulated, and its infiltration into the ground is limited to less than the hydraulic conductivity of the soil.

Soil temperature is determined in two layers by the force-restore method of Deardorff (1978). Soil moisture, which is predicted from diffusion equations in three layers, is increased by infiltrated precipitation and snowmelt, and is depleted by evapotranspiration, direct evaporation, and drainage. Both surface runoff and deep runoff from gravitational drainage are simulated.

Sea Ice

Sea ice is represented as a horizontally uniform slab without snow or leads. Brine rejection processes are not parameterized; instead, an enhanced but seasonally invariant salinity forcing similar to that of England (1993) is imposed near Antarctica to account for the effects on the thermohaline circulation.

The ice albedo is a constant 0.5 and the solar penetration through the ice is set to 0.068. Ice formation, accretion, and ablation are determined by the net balance among the atmospheric heat fluxes at the top surface of the ice, the oceanic turbulent heat flux at the bottom of the ice, and the conductive heat flux within the ice. The atmospheric heat flux is calculated after Haney (1971) in the same way as over open ocean, except for inclusion of the ice albedo and latent heat of evaporation. The heat flux at the ice bottom is proportional to the temperature of the underlying ocean and the salt-water freezing point temperature. A simple thermodynamic model after Semtner (1976) and Parkinson and Washington (1979) calculates temperatures within the sea ice from one-dimensional heat equations.

Sea ice rheology and dynamics are neglected.

Chief Differences from Closest AMIP Model

The principal features of the IAP/LASG atmospheric model are documented by Wu et al. (1996). Besides a reduction in horizontal resolution (to R15), the chief differences from the closest AMIP model, BMRC BMRC2.3 (R31 L9) 1990, include:

Atmospheric Dynamics

As an alternative to the AMIP model formulation, the atmospheric equations are expressed as perturbations from the state of a reference atmosphere in order to reduce truncation errors near mountains (cf. Zeng 1979).

Radiation

The k-distribution method of Shi (1981) and Wang (1996) replaces the radiation scheme of the AMIP model.

Cloud Formation

The diagnostic cloud formation scheme described by Liu et al. (1997) replaces that of the AMIP model.

Land Surface Processes

The Simple SiB (SSiB) land surface scheme of Xue et al. (1991) replaces that of the AMIP model . The resulting land surface climate is described by Liu and Wu (1997).

References

Deardorff, J.W., 1978: Efficient prediction of ground surface temperature and moisture, with inclusion of a layer of vegetation. J. Geophys. Res., 83, 1889-1903.

England, M.H., 1993: Representing the global-scale water masses in ocean circulation models. J. Phys. Oceanogr., 23, 1523-1552.

Esbensen, S.K., and Y. Kushnir, 1981: Heat budget of the global ocean: Estimates from surface marine observations. Report No. 29, Climate Research Institute, Oregon State University, Corvallis, Oregon, 271 pp.

Haney, R.L., 1971: Surface thermal boundary condition for ocean circulation models. J. Phys. Oceanogr., 1, 241-248.

Hellerman, S., and M. Rosenstein, 1983: Normal monthly wind stress over the world ocean with error estimates. J. Phys. Oceanogr., 13, 1093-1104.

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

Liu, H., X.-Z. Jin, X.-H. Zhang, and G.-X. Wu, 1996: A coupling experiment of an atmosphere and an ocean model with a monthly anomaly exchange scheme. Advances in Atmospheric Sciences, 13, 133-146.

Liu, H., and G.-X. Wu 1997: Impacts of land surface on July mean climate and onset of the monsoon: A study with an AGCM plus SSiB. Adv. Atmos. Sci., 14, No. 3, 289-308.

Liu, H., X.-H. Zhang, and G.-X. Wu, 1998: Cloud feedback on SST variability in the Western Equatorial Pacific in a CGCM. Adv. Atmos. Sci. (in press).

Parkinson, C.L. and W.M. Washington, 1979: A large-scale numerical model of sea ice. J. Geophys. Res., 84, 311-337.

Sellers, P.J., Y. Mintz, Y.C. Sud, and A. Dalcher, 1986: A simple biosphere model (SiB) for use within general circulation models. J. Atmos. Sci., 43, 505-531.

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

Shi, G.-Y., 1981: An accurate calculation and representation of the infrared transmission function of the atmospheric constituents. Ph.D. Thesis, Department of Atmospheric Science, Tohoku University of Japan, 191 pp.

Wang, B., 1996: On the radiation transfer models for climate simulation. Ph.D. Thesis, Institute of Atmospheric Physics/Chinese Academy of Sciences, Beijing, China, 92 pp. (in Chinese).

Wu, G.-X., L. Hui, Y.-C. Zhao, and W.-P. Li, 1996: A nine-layer atmospheric general circulation model and its performance. Advances in the Atmospheric Sciences, 13, 1-18.

Xue, Y.-K., P.J. Sellers, J.L. Kinter II, and J. Shukla, 1991: A simplified biosphere model for global climate studies. J. Climate, 4, 345-364.

Yu, Y.-Q., 1997: Design of a sea-air-ice coupling scheme and a study of numerical simulation of interdecadal oscillation of climate. Ph.D. thesis, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, 130 pp. (in Chinese).

Yu, Y.-Q., and X.-H. Zhang, 1997: A modified sea-air-sea ice coupling scheme. To appear in Chinese Bulletin (in Chinese).

Zeng, Q.-C., 1979: Physical and Mathematical Basis of Numerical Weather Prediction. Science Press, Beijing, 543 pp. (in Chinese).

Zhang, X.-H., N. Bao, R.-C. Yu, and W.-Q. Wang, 1992: Coupling scheme experiments based on an atmospheric and an oceanic GCM. Chinese Journal of Atmospheric Sciences, 16(2), 129-144.

Zhang, X.-H., K.-M. Chen, Z.-Z. Jin, W.-Y. Lin, and Y.-Q. Yu, 1996: Simulation of thermohaline circulation with a twenty-layer oceanic general circulation model. Theoretical and Applied Climatology, 55, 65-88.

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

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