|Last update: Tuesday, 30-Sep-2008 16:11:54 CEST|
Eddy Features in the Ocean Surface Wind Field from Multifrequency HF Radar, Field Anemometers and a Meteorological Model
Jessica A. Drake, John F. Vesecky, and Kenneth Laws
Frank L. Ludwig and Calvin C. Teague
Jeffery R. Paduan
Features in the ocean surface wind field are seldom observed at spatial scales below many tens to hundreds of kilometers because of sparse measurements at sea and the same is often true over land. We have developed a system to utilize both HF radar and surface anemometer measurements to synthesize a wind field map with a resolution of about 5 km covering both coastal sea and land. Previously we have demonstrated how multifrequency HF radar observations can be used to estimate ocean wind vectors on a 3 km grid to an accuracy of about 1.5 m/s and 25° in speed and direction respectively using 4 frequency radar data from Multifrequency Coastal Radar (MCR) systems. Here we summarize results of adapting these methods to the currently available mix of MCR and single frequency Codar, SeaSonde systems on and near Monterey Bay. First, we briefly demonstrate the operation of our HF radar surface wind measurement system over Monterey Bay, California. We then report on application of the winds on continuous streamline surfaces (WOCSS) method to assimilate these HF wind estimates together with anemometer measurements from land and from ocean buoys in the observational area. Software has been developed to collect the necessary data from both radars and anemometers and generate wind field maps on a 5 km grid with a latency of about an hour. The results cover the sea and land area from the north end of San Francisco Bay to beyond the south end of Monterey Bay (180 km) and about 140 km from east to west over San Francisco and Monterey Bays and surrounding land and ocean. Further, we present observations (stills & movie) of a 15 km-sized surface wind eddy near the north end of Monterey Bay that persists for 2 to 3 hours. Wind eddies on Monterey Bay have been deduced from anemometer data by Archer, Ludwig, et al. and are thought to be a common cause of fog in the Santa Cruz city area. The observations presented here provide a detailed map of the wind field, especially over the ocean, and thus provide the data to study these eddies more quantitatively. We hope that routine observations of this type will be assimilated into regional weather forecast models, e.g. COAMPS, and contribute to more skillful weather forecasts in coastal regions.