Spectral analysis of the T-REX high-frequency towers data

Many unresolved issues exist in the analysis of the turbulence measurements in complex mountainous terrain. For calculation of means and higher order moments, time series are needed that are long enough to include all the relevant low-frequency contributions to the process that is addressed. Also, the time series must be sampled at rates fast enough to capture all the high-frequency contributions. Improper choices of averaging times and sampling rates can compromise statistics which leads to wrong representation of turbulence.

The Terrain-induced Rotor Experiment (T-REX) has provided an unprecedented data set that allows the investigation of temporal and spatial turbulence characteristics in a variety of atmospheric conditions in complex terrain. Three towers were installed by NCAR at three different locations in the Owens Valley. Each tower was 35 m tall and instrumented with multiple CSAT3 ultrasonic anemometers collecting data with a sampling rate of 60 Hz. A case study is presented of a high wind event over the Owens Valley that occurred on 02 March 2006 during the T-REX Intensive Observation Period 1. On the basis of the spectral analysis of the towers data, we are looking for the proper time averaging scale in order to define turbulent perturbations which are used for the evaluation of turbulent properties during this event. Results of this study could lead to important recommendations for the analysis and parameterization of turbulence in complex terrain.