Comparing models and observations of boundary-layer clouds at Graciosa Island

Description

We use the Atmospheric Radiation Measurement Mobile Facility (AMF) data set at Graciosa Island, Azores, spanning May 2009–December 2010, to evaluate the performance of two numerical weather prediction models in predicting boundary-layer clouds in this subtropical marine environment. We are particularly interested in quantifying how well these models can simulate the diurnal cycle as well as synoptic-to-seasonal variability in low clouds. We compare the AMF observations to column predictions by the National Center for Atmospheric Research Global Forecasting System (NCEP GFS) and the European Center for Medium-Range Weather Forecasting (ECMWF), as well as to satellite observations. Preliminary results indicate that model errors in winds are larger than expected, possibly due to island effects. Errors in temperature occur primarily due to errors in the boundary-layer depth. Relative humidity errors are large.