Indication for Biases in Dry Intrusions and the Marine Boundary Layer Over the Azores in ECMWF Short-Term Forecasts and Analyses

The model representation of dry intrusions (DIs) and the marine boundary layer (MBL) is analyzed in the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS). For this purpose, a DI classification at the Azores is combined with observation, short-term background forecast and analysis data from the IFS data assimilation system. The background exhibits a cold bias in the descending DI, which is possibly related to a cold bias in the MBL below through vertical mixing. At the surface, simulated wind speeds are underestimated and directions are veered compared to the observations. The errors are reduced in the analysis except for near-surface wind and humidity biases. We hypothesize that these biases are connected through underestimated surface latent heat fluxes. Such persistent biases potentially influence local weather and midlatitude weather evolution as cyclones are supplied with moisture from the cold sector influenced by DIs.