Modelling of channelled winds in high wind areas of New Zealand
The areas of most interest for wind energy development in New Zealand are at gaps or low points in the main mountain ranges where mean speeds at a number of sites have been found to exceed 10 m/s. In these areas, the channelling of the winds by the mountains is shown by high frequencies of winds in the direction through the gap and by high mean speeds. WAsP (Wind Atlas Analysis and Application Programme), has been used to predict the mean speed and direction frequencies at ten anemometer stations in these areas, based on the wind frequencies at the 900 hPa level at radar-wind stations in the same areas. The use of the radar-wind data simplifies the wind-atlas computation in WAsP. The wind speed prediction at one relatively isolated hill is found to be very close to that observed. However at sites with more pronounced channelling, WAsP underpredicts both the mean speed and the predominance of the channelled directions. By applying parameters which simulate the presence of an inversion above the boundary layer, WAsP can be successfully used to predict the mean speed and direction frequencies at the stations affected by channelling. Analyses of the effect of map size on the wind prediction have shown the importance of the constraining influences of the large scale mountain systems on surface wind climate. In this way, WAsP has value as an analysis tool but the predictions lack generality in complex mountain systems.