Turbulence, shear and stability influences on lower boundary-layer wind profiles

Sodar measurements provide a wealth of information about the state of the lower atmospheric boundary layer. Such information is crucial for the accurate assessment of the wind resource at a site, as well as being important for predicting wind turbine power performance. Data provided at 10 m height intervals include horizontal wind speed, wind direction, vertical wind speed and flow inclination, vertical turbulence intensity, and signal amplitude profiles. In addition, with each sodar an array of surface meteorological parameters are collected that may include any of the following: wind speed and direction, temperature, humidity, solar radiation, and precipitation.

For this paper we have compiled data from 30 locations out of the more than 130 sodar campaigns we have conducted in North America and Hawaii, representing a range of terrain and cover types. Using a variety of stability measures and classifications derived from the sodar data and the ancillary measurements, we will show how the wind profile varies over longer periods, for example, seasonally, in response to stability effects, as well as over periods of a few hours in response to transient phenomena. Wind profile variation will be related to turbine power performance and illustrated using animated sequences of wind profiles.