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On the Use of Lower Saturation Criteria for Release of Latent Heat in NWP Models

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  • 1 National Meteorological Center, Washington, DC 20233
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Abstract

In several numerical models the large-scale release of latent heat is evaluated when the mixing ratio q exceeds a certain fraction (SATRH < 1) of its saturation value qs. The predicted mixing ratio at the end of a time step in the above case is always less than qs. It is shown that when a fractional value of SATRH is used in the model, the net heating of the atmosphere is significantly weaker than when the release of latent heat in the model is evaluated at supersaturated grid points only. Results of integrations with a symmetric hurricane model show that the intensity of the simulated storm is therefore weaker when a lower value of SATRH is used.

Abstract

In several numerical models the large-scale release of latent heat is evaluated when the mixing ratio q exceeds a certain fraction (SATRH < 1) of its saturation value qs. The predicted mixing ratio at the end of a time step in the above case is always less than qs. It is shown that when a fractional value of SATRH is used in the model, the net heating of the atmosphere is significantly weaker than when the release of latent heat in the model is evaluated at supersaturated grid points only. Results of integrations with a symmetric hurricane model show that the intensity of the simulated storm is therefore weaker when a lower value of SATRH is used.

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