Analysis of the Mean Forcing Fields Simulated By the Two-level, Mintz-Arakawa Atmospheric Model

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  • 1 The Rand Corporation, Santa Monica, Calif.
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Abstract

The global distributions of the mean January surface wind stress, the net diabatic heating rate, and the net rate of moisture addition as simulated in a 30-day integration with the two-level, Mintz-Arakawa atmospheric general circulation model are presented. The latitudinal distributions of the zonal averages of these forcing fields are shown to be in reasonable agreement with the available observations. The most prominent discrepancies are evidently due to the model's simulation of excessive convective precipitation (and the associated convective latent heating) in the Tropics, especially in the Northern (winter) Hemisphere. The zone of simulated tropical precipitation extends some 15° poleward of the observed position and results in a corresponding distortion of the field of evaporation-minus-precipitation (or moisture-addition rate).

In determining the monthly mean forcing fields, one must be particularly accurate in accumulating the (convective) precipitation rate during the integration; the customary use of 6-hourly fields results in a sampling error as large as 25 percent for even the zonally averaged rainfall. With the exception of a small sampling error in the mean rate of absorption of solar radiation, the components of the other forcing fields are satisfactorily determined by 6-hourly data.

Abstract

The global distributions of the mean January surface wind stress, the net diabatic heating rate, and the net rate of moisture addition as simulated in a 30-day integration with the two-level, Mintz-Arakawa atmospheric general circulation model are presented. The latitudinal distributions of the zonal averages of these forcing fields are shown to be in reasonable agreement with the available observations. The most prominent discrepancies are evidently due to the model's simulation of excessive convective precipitation (and the associated convective latent heating) in the Tropics, especially in the Northern (winter) Hemisphere. The zone of simulated tropical precipitation extends some 15° poleward of the observed position and results in a corresponding distortion of the field of evaporation-minus-precipitation (or moisture-addition rate).

In determining the monthly mean forcing fields, one must be particularly accurate in accumulating the (convective) precipitation rate during the integration; the customary use of 6-hourly fields results in a sampling error as large as 25 percent for even the zonally averaged rainfall. With the exception of a small sampling error in the mean rate of absorption of solar radiation, the components of the other forcing fields are satisfactorily determined by 6-hourly data.

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