Testing clouds and radiation in atmospheric models

Date: 19.11.2015

Time: 11:00 - 12:00

Place: Nordlys, DMI

Contact: Cathrine Fox Maule

Classically the criteria to assess the quality of an atmospheric model are the synoptic variables: Pressure, wind speed, wind direction, temperature, relative humidity, precipitation and cloud cover. In recent years, the surface radiation balance and cloud properties have been added to this list of essential atmospheric climate variables (e.g. GCOS-195 2015). Today we have very good forecasts of pressure and wind, reasonable forecasts of temperature, relative humidity and precipitation, but forecasting clouds and fog remains one of the biggest issues with operational numerical weather prediction (NWP). Climate models also give very different cloud radiative forcings. Within the ALADIN-HIRLAM consortium and the IEA SHC expert group on solar resource assessment and forecasting, tests have been performed of NWP models that include testing the internal calculations of optical properties and radiative transfer, and the bottom line solar irradiance as measured at the surface. The results illustrate the challenges that remain in cloud forecasting and the usefulness of assessing the quality of solar irradiance forecasts. A particular focus is given to high temporal and spatial variability, also at sub-grid level in the models, and how this affects the large scale radiation balance.