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Convective Closure Assumptions

 

Different from previous versions, V2.2, by default, uses a ``nonlinear tex2html_wrap_inline1877 '' scheme for convective closure assumption. It is in principle the same as the original Betts-Miller convective closure scheme but retains the nonlinear Clausius-Clapeyron dependence of tex2html_wrap_inline1879 (the convective moisture profile) on temperature in horizontal variations as well as vertical. In the original scheme, linearization is used about a reference profile at each level, which holds well through the tropics, but is beyond its range of validity in mid-latitudes in winter. The nonlinear scheme significantly reduces the excessive mid-latitude precipitation shown in the original model and prevents occurrence of negative humidity in mid-latitudes. The original linear scheme is commented out in qtcm.F.

Another convective closure assumption implemented but commented out in qtcm.F is called the `unshifted- tex2html_wrap_inline1881 scheme' or `U- tex2html_wrap_inline1881 scheme', which assumes that the convective temperature profile, tex2html_wrap_inline1881 , arises following a moist adiabat from the boundary layer without the shift used in the original Betts-Miller scheme to match the moisture sinks. This condition is indeed applied to the moisture sink term. It avoids explicitly specifying convective moisture profile. Simulations with this scheme produce similar results to the original linear scheme. Implications of this scheme and Comparison of the model results using different convective schemes are discussed in detail in Su et al. [10].



Hui Su
Thu Nov 16 00:53:31 PST 2000