Comparison of MM5 and meteorological buoy winds from British Columbia to northern California

Abstract

Numerical ocean modelling requires reliable marine wind fields for accurate simulation of ocean circulation. This study compares winds from the University of Washington operational Pennsylvania State/National Center for Atmospheric Research Mesoscale Model 5 (MM5) atmospheric model to winds observed at coastal meteorological buoys from British Columbia to northern California, in order to assess their suitability for use in regional ocean modelling for the ECology and Oceanography of Harmful Algal Blooms (ECOHAB) program. Two three-month study periods from 2003 were chosen: summer (July to September), which is most important for the growth of toxic Pseudo-nitzschia off the Washington State coast, and fall (October to December) when downwelling favourable winds comforce the onshore movement of potentially contaminated shelf water. MM5 12-km resolution model wind speeds ranged from 81 to 101% of observed wind speeds. Mean winds were well modelled in the summer, but showed a 35° (average) clockwise direction bias in the fall compared to buoy winds. Winds were strongest in the diurnal and 2-5 day period weather bands in both seasons; spectral coherences between the model and observed winds in both firequency bands were highest (0.66-0.93) off the Washington State coast and northern Vancouver Island. In isolated near-shore cases, model wind characteristics were significantly different from those observed due to near-shore processes that were not accurately captured by the model. © Canadian Meteorological and Oceanographic Society.