Evaluation of forecasted southeast Pacific stratocumulus in the NCAR, GFDL, and ECMWF models

Forecasts of southeast Pacific stratocumulus at 20°S and 85°W during the East Pacific Investigation of Climate (EPIC) cruise of October 2001 are examined with the ECMWF model, the Atmospheric Model (AM) from GFDL, the Community Atmosphere Model (CAM) from NCAR, and the CAM with a revised atmospheric boundary layer formulation from the University of Washington (CAM-UW). The forecasts are initialized from ECMWF analyses and each model is run for 3-5 days to determine the differences with the EPIC field observations.

Observations during the EPIC cruise show a well-mixed boundary layer under a sharp inversion. The inversion height and the cloud layer have a strong and regular diurnal cycle. A key problem common to the models is that the planetary boundary layer (PBL) depth is too shallow when compared to EPIC observations.