7B.4 Role of synoptic- and meso-scales in the momentum budget in a coastal environment: multi-year observational and modeling study

Jimenez, Pedro A., CIEMAT, J. Vila-Guerau de Arellano, Wageningen University, J. Dudhia, National Center for Atmospheric Research, and Fred C. Bosveld, Royal Netherlands Meteorological Institute

We investigate the combined role of synoptic- and meso-scales in the momentum budget in a coastal environment. The analysis is based on observations of the wind profile within the lowest 200 m of the atmosphere recorded during a 10 year period (2001 - 2010) at a tower in the Cabauw Experimental Site for Atmospheric Research (CESAR, The Netherlands); and WRF simulations at high horizontal resolution of 2 km spanning the complete observational period. In analyzing the whole period, results indicate that WRF is able to reproduce the inter-annual wind variability but with a tendency to be too geostrophic. In the study of the intra-annual variability, we find a different behavior between the Winter and the Summer season being the Spring and Autumn transition seasons. Briefly, the winter momentum budget shows a weak intradiurnal variability. The synoptic scale controls the shape of the near surface wind profile that is characterized by a weaker and more ageostrophic winds near the surface than at higher altitudes within the planetary boundary layer as a result of the frictional turning. In turn, during summer, mesoscale circulations associated with the differential heating of land and sea become important including a stronger intradiurnal component that is responsible for an oscillation of the near surface winds around the geostropic direction with the maximum departure in the afternoon. The contribution of this mesoscale component depends on the specific orientation of the coast. Our findings stress the importance to evaluate and understand the performance of WRF with multi-year observational/simulated data sets in order to determine the limitations of surface layer and boundary-layer parameterizations.