Conservation of Moisture in a Hybrid Kuo-Type Cumulus Parameterization

Abstract

The conservation of moisture requirement used in a hybrid Kuo-type cumulus parameterization scheme is generalized so that the source of moisture for the cumulus process originates from all layers below the level of condensation, including the subcloud layer(s). This conservation scheme is distinctly different than those used with the traditional Kuo-type cumulus parameterizations, which do not include convective-scale vertical transport involving the subcloud layer(s). Numerical forecasts with the modified conservation scheme are compared with those obtained using the conventional approach that extracts the moisture from the grid-scale moisture field at the level of condensation. Radiosonde observations and Geostationary Operational Environmental Satellite (GOES) observed brightness temperatures for water vapor channel 3 (6.7 ?m) are used to verify the lower- and upper-tropospheric moisture fields, respectively. Forecast statistics, including precipitation as measured against rain gauge reports, are all improved by using the generalized moisture conservation approach. Removing moisture from the subcloud layer(s) helps stabilize the sounding and promotes self-regulation of the convection. Including the subcloud layer(s) also alters the evolution and duration of some moist convective events. In contrast, an unregulated subcloud layer encourages the moist parameterization to produce excessive precipitation.