A convective wake parameterization incorporated into the single-column (SCM) version of the NCAR Community Climate Model CCM3 is tested using observational data from 12 squall line cases to determine whether it can successfully reproduce convectively driven wakes in a global climate model. The key spatial, thermodynamic, and kinematic properties of the modeled versus tile observed wakes are examined, as these features determine the effects of the wakes on surface fluxes and the initiation of convection, effects that should be simulated correctly in general circulation models if deep convection and the resulting earth-atmosphere energy exchanges are to be adequately represented. Results from these simulations indicate that, while the SCM-convective wake scheme combination generally produced long-lasting squall/wake systems, the wakes were often too shallow, too warm, and too moist. These differences occurred despite the ability of CCM3's standard cumulus parameterization to provide the wake scheme with air whose thermodynamic properties were essentially unbiased, although poorly correlated to the case-by-case observations. As a result of these differences, the modeled wakes propagated at speeds that were somewhat lower than those observed. Despite these problems, it is also demonstrated that the wake scheme does act to significantly improve the response of the model's cumulus downdraft parameterization to case-to-case variations in the presquall environments; that is, it improves upon the correlation between the thermodynamic characteristics of the modeled downdrafts and the thermodynamic changes across the gust fronts of the observed wakes. A test case using an environmental wind and shear effect formulation derived from the mesoscale modeling work of Liu and Moncrieff demonstrated that the differences between previously published descriptions of these effects remain large enough to significantly affect cold pool behavior in the convective wake parameterization.
|Original language||English (US)|
|Number of pages||15|
|Journal||Monthly Weather Review|
|Issue number||6 II|
|State||Published - Jun 1999|
All Science Journal Classification (ASJC) codes
- Atmospheric Science