OCEAN WINDS OCEAN WIND Ocean wind is defined

OCEAN WINDS

OCEAN WIND • Ocean wind is defined as the motion of the atmosphere relative to the surface of the ocean. • Most common reference height for near surface ocean wind measurements: 10 meters above sea level.

MEASUREMENT OF OCEAN WIND In situ • Buoys, ships or platforms through mechanical anemometer. Remote Sensing • Ground-based – Ground-based Doppler radar: using inbound and outbound radial velocities. • Airborne – Passive microwave: based on distinct roughness pattern of ocean surface caused by motion of air above the ocean surface (“brightness”) which can be only observed by passive microwave radiometers; with right combination specific microwavelengths and processing algorithms, the “brightness” can be translated to near-surface wind speed. E. g. SSM/I, SSMIS, TMI, AMSR-2, AMSR-E, GMI. – Active microwave: based on the characteristic of centimetre-scale ocean surface waves known as capillary waves (Bragg scattering) which can be observed by specifically tuned airborne radars. These airborne radars transmit microwave pulses of energy to the ocean surface, which immediately scatters a portion of the reflected energy back to the radar. Once the radar cross section is normalized, the near -surface wind speed can be computed as a function of the backscattered energy. Active radar system can combine measurements from different azimuth angles to derive the approximate direction of the wind. E. g. Wind. Sat, Quik. Scat, Sea. Winds, ASCAT.

REANALYSIS WIND DATA • Combination of wind data from in situ and remote sensing wind data into numerical weather prediction model. • E. g. – Climate Forecasting System Reanalysis (CFSR) – Climate Four Dimensional Data Assimilation (CFDDA) – Modern Era-Retrospective Analysis for Research and Applications (MERRA) – National Centres for Environmental Prediction (NCEP)/ National Centre for Atmospheric Research (NCAR) Reanalysis – European Centre for Medium Range Weather Forecast (ECMWF) Reanalysis (ERA -Interim) • Global atmospheric reanalysis from 1979, continuously updated in real time. • 128 available atmospheric parameters.