Wind Direction Analysis

In the next couple of months wind direction measurements will be available over the current WERA footprint.

A new technique for measurements of wind direction was developed by Lucy Wyatt, by measuring the directional spectrum of high-frequency ocean wave using HF radar (Wyatt L.R., L.J. Ledgard,C.W. Anderson, 1997. “Maximum likelihood estimation of the directional distribution of 0.53Hz ocean waves.” Journal of Atmospheric and Oceanic Technology, 14 591-603). This new technique is based on Donelan's directional spreading model (Donelan, M. A., J. Hamilton, and W. H. Hui, 1985: Directional spectra of wind-generated waves. Philos. Trans. Roy. Soc. London, Ser. A; 315, 509-562). The wind direction is determined from the difference in amplitude of the two main Bragg peaks in the radar power spectrum at each grid point across the coverage area.

The directionality of the surface winds lies in the Doppler spectra at each of the radar cells (>5000). Wind directions are estimated using the ratio of the two Bragg peaks in the spectrum. Inferring the surface winds requires an assumption concerning the wind only drives the local wind waves (Wyatt 2005) where the waves are derived from the second-order returns in the Doppler spectra.