Vertical Eddy Heat Fluxes from Model Simulations

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  • 1 Center for Meteorology and Physical Oceanography, Massachusetts Institute of Technology, Cambridge, Massachusetts and NASA/Goddard Space Flight Center, Institute for Space Studies
  • 2 ST Systems Corporation, NASA/Goddard Space Flight Center, Institute for Space Studies, New York, New York
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Abstract

Vertical eddy fluxes of heat are calculated from simulations with a variety of climate models, ranging from three-dimensional GCMs to a one-dimensional radiative-convective model. The models’ total eddy flux in the lower troposphere is found to agree well with Hantel's analysis from observations, but in the mid- and upper troposphere the models’ values are systematically 30% to 50% smaller than Hantel's. The models nevertheless give very good results for the global temperature profile, and the reason for the discrepancy is unclear. The model results show that the manner in which the vertical eddy flux is carried is very sensitive to the parameterization of moist convection. When a moist adiabatic adjustment scheme with a critical value for the relative humidity of 100% is used, the vertical transports by large-scale eddies and small-scale convection on a global basis are equal; but when a penetrative convection scheme is used, the large-scale flux on a global basis is only about one-fifth to one-fourth the small-scale flux. Comparison of the model results with observations indicates that the results with the latter scheme are more realistic. However, even in this case, in mid- and high latitudes the large and small-scale vertical eddy fluxes of heat are comparable in magnitude above the planetary boundary layer.

Abstract

Vertical eddy fluxes of heat are calculated from simulations with a variety of climate models, ranging from three-dimensional GCMs to a one-dimensional radiative-convective model. The models’ total eddy flux in the lower troposphere is found to agree well with Hantel's analysis from observations, but in the mid- and upper troposphere the models’ values are systematically 30% to 50% smaller than Hantel's. The models nevertheless give very good results for the global temperature profile, and the reason for the discrepancy is unclear. The model results show that the manner in which the vertical eddy flux is carried is very sensitive to the parameterization of moist convection. When a moist adiabatic adjustment scheme with a critical value for the relative humidity of 100% is used, the vertical transports by large-scale eddies and small-scale convection on a global basis are equal; but when a penetrative convection scheme is used, the large-scale flux on a global basis is only about one-fifth to one-fourth the small-scale flux. Comparison of the model results with observations indicates that the results with the latter scheme are more realistic. However, even in this case, in mid- and high latitudes the large and small-scale vertical eddy fluxes of heat are comparable in magnitude above the planetary boundary layer.

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