An Evaluation of the diurnal cycle in the Multiscale Modeling Framework using satellite data

Multiscale Modeling Framework (MMF), or "superparameterization", was proposed to improve the representation of convection and clouds in general circulation models (GCMs). In MMF, a cloud resolving model (CRM) is implemented at each GCM column to replace traditional parameterizations. In this study, we evaluate diurnal cycles in MMF by applying an infrared (IR) brightness temperature and a precipitation radar (PR) reflectivity simulator to CRM grid data in MMF. Simulator results were then compared with infrared radiance data from Geo-stationary satellite and precipitation radar data from Tropical Rainfall Measurement Mission (TRMM). While the actual surface precipitation rate in the MMF has a reasonable diurnal phase and amplitude when compared with TRMM observations, the IR simulator results indicate an inconsistency in the diurnal anomalies of high-level clouds between the model and the Geo-stationary satellite data. Primarily due to its excessive high-level clouds, the MMF overestimates the simulated precipitation index (an indicator for deep convection activity) and fails to reproduce the observed diurnal cycle phase relationships among precipitation index, high-level clouds and upper troposphere relative humidity. The PR simulator results show that over the tropical oceans, the occurrence fraction of reflectivity in excess of 20 dBZ is almost one order of magnitude larger than the TRMM data at altitudes above 6 km. Both results suggest that the MMF oceanic convection is overactive. Furthermore, the joint distribution of simulated IR brightness temperature and PR reflectivity indicates that the most intense deep convection is found more often over tropical land than ocean, in agreement with previous observational studies.