WRF and The Marine Planetary Boundary Layer Olav Krogsæter 1,2 Joachim Reuder 2 Gard Hauge 1 1 StormGeo / 2 University of Bergen, Norway olav.krogsaeter@stormgeo.com 1. Introduction Offshore wind energy is a rapidly growing field worldwide, both in a scientific, engineering, and in an economical point of view. In Europe 140 GW offshore wind projects are already in different planning stages, and at the time of writing 1136 offshore wind turbines are installed and connected to the European power grid. By 2020 the offshore wind power's economical potential in Europe is between 60% and 70% of the projected electricity demand 1 The are many different scientific aspects between onshore and offshore wind energy. Perhaps the most obvious one is that we are dealing with a moving surface at the bottom boundary, namely ocean waves. Not very complex compared with valleys and mountains, as we have onshore, but complex enough to significantly alter both the mean and turbulent behaviour of the wind field in the Marine Boundary Layer (MBL), compared with a flat non-moving surface. Some LES-studies have already shown how the waves influences the wind field in the MBL, e.g. Sullivan et.al. (2010). Here we will show some preliminary results on important atmospheric parameters connected to offshore wind energy in the MBL. To perform these sensitivity tests we have run the WRF-model for a whole year with 5 different PBL-schemes. The initialization- and boundary data are from the ERA-Interim dataset from ECMWF in England. The results are primarily compared with observations from the German research platform FINO1 in Southern North Sea. From this platform there exists meteorological and oceanographical observations back to 2004 with both wind (1 Hz and 10 Hz time resolution) and temperature measurements for every 10th meter from 30 to 100 m above sea level. 2. Experiment setup WRF3.2.1 is used throughout this study, and is run on a Cray XT4 system at Uni Computing in Bergen, Norway, with 384 CPUs for this project. 1 http://www.ewea.org/index.php?id=203 2.1 Resolution Three two-way nested domains are used with 27, 9, and 3 km horizontal resolution, Figure 1. The outermost domain is covering the whole NE-Atlantic, included Iceland, such that the main Low pressure systems, which almost always are moving in from the west, are within the domain. The vertical resolution is 20 m from 0 m to 200 m. 50 m from 200 m to 500 m. 100 m from 500 m to 1000 m. 250 m from 1000 m to 5000 m. 500 m from 5000 m to 20 000 m. The time step had to be set to 120s to fulfil the CFL-criteria. 2.2 Physics schemes Micro physics: New Thompson scheme with ice, snow and graupel, suitable for high resolution simulations. Long wave and short wave radiation: RRTMG schemes. Land-surface: RUC land surface model, six soil layers, multilayer snow and frozen soil. Cumulus parametrization: Grell 3D scheme with shallow convection turned on. Whether to use or not to use cumulus Figure 1: Horizontal domain and the German research platform Fino1.