Gd. Alexander et Wr. Cotton, THE USE OF CLOUD-RESOLVING SIMULATIONS OF MESOSCALE CONVECTIVE SYSTEMS TO BUILD A MESOSCALE PARAMETERIZATION SCHEME, Journal of the atmospheric sciences, 55(12), 1998, pp. 2137-2161
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).