THE USE OF CLOUD-RESOLVING SIMULATIONS OF MESOSCALE CONVECTIVE SYSTEMS TO BUILD A MESOSCALE PARAMETERIZATION SCHEME

A method is described for parameterizing thermodynamic forcing by the mesoscale updrafts and downdrafts of mesoscale convective systems (MCS s) in models with resolution tao coarse to resolve these drafts. The p arameterization contains improvements over previous schemes, including a more sophisticated convective driver and inclusion of the vertical distribution of various physical processes obtained through conditiona l sampling of two cloud-resolving MCS simulations. The mesoscale param eterization is tied to a version of the Arakawa-Schubert convective pa rameterization scheme that is modified to employ a prognostic closure. The parameterized Arakawa-Schubert cumulus convection provides conden sed water, ice, and water vapor, which drives the parameterization for the large-scale effects of mesoscale circulations associated with the convection. In the mesoscale parameterization, determining thermodyna mic forcing of the large scale depends on knowing the vertically integ rated values and the vertical distributions of phase transformation ra tes and mesoscale eddy fluxes of entropy and water vapor in mesoscale updrafts and downdrafts. The relative magnitudes of these quantities a re constrained by assumptions made about the relationships between var ious quantities in an MCS's water budget deduced from the cloud-resolv ing MCS simulations. The MCS simulations include one of a tropical MCS observed during the 1987 Australian monsoon season (EMEX9) and one of a midlatitude MCS observed during a 1985 field experiment in the Cent ral Plains of the United States (PRE-STORM 23-24 June).