Monday, 3 June 2002
An Intercomparison of MMCR and NCEP Global Model Clouds at the ARM SGP Site
In conjunction with the National Center for Environmental Prediction (NCEP), the University of Utah has been archiving (daily) column data from the NCEP Medium Range Forecast (MRF) model for various sites over the globe. Four of these sites coincide with ARM facilities at Manus, Nauru, Barrow, and the Southern Great Plains Central Facility. Within the past year, the MRF experienced a significant upgrade in its cloud scheme - switching from a diagnostic to prognostic large-scale condensate scheme. Additionally, the rh-based subgrid scale stratiform cloud fraction parameterization is now a function of both large-scale relative humidity and the predicted cloud water/ice. Herein we focus on the short-term prediction of cloud amount by comparing diurnal composites of MRF and MMCR cloud fraction (using 3 h forecasts from model forecast hours 12 to 48). We also examine the validity of the MRF random overlap assumption by estimating the actual cloud overlap using data obtained from the MMCR at the ARM sites. Statistics are presented for 2001 and stratified by season.