Using The WRF Model To Simulate Flow Through California’s Altamont Pass

The generation of electrical power by extracting the energy of the wind has become a significant source of energy for many parts of the world including the United States. In fact, wind power has been the fastest growing source of energy during the last fifteen years. California's Altamont Pass is the site of the earliest intensive development of wind energy. Today there are hundreds of operational wind turbines located in the pass making is a data rich location very suitable for model research studies.

The Altamont Pass is a gap in the series of hills between the San Francisco Bay area and the San Joaquin Valley. Strong near-surface winds often develop there as a part of a thermally direct circulation driven by the temperature difference between the hot valley to the east and the cooler maritime air to the west. The generally southwesterly winds tend to be strongest in the warm season, and often reach a peak during the nighttime hours, with mean monthly wind speeds as high as 20 m/s.

To properly support operational wind farms, there is a need for 0-48 hour forecasts of wind power generation to within 10-20% accuracy. This requirement in turn demands highly accurate localized forecasts of the wind speed and generation at the wind turbine height (usually about 50 m above the surface). The flow is often shallow (~100 m) and strongly interacts with the complex terrain, with strong variations on scales of hundreds of meters. Forecasting these winds and the resulting wind power generation has been a challenging problem. A group at The University of California, Davis has used a wind tunnel to simulate neutral boundary layer flow through the Pass, attempting to predict flow at individual wind turbine sites. MESO, Inc. has used its MASS model at 100 m resolution with the same goal, accurately representing the spatial pattern of wind speeds in the Pass for a range of conditions.

The 2.0 version of the Weather Research and Forecasting (WRF) model has been developed by the National Center for Atmospheric Research (NCAR) and various government agencies as a next-generation community mesoscale model suitable for application to a wide range of atmospheric problems. In this research, the WRF model will be used to simulate the flow through the Altamont Pass at high resolution in order to examine its suability to support wind energy operations. Results will be compared to those from the other methods described above.