An observational, stability-based estimate of 80 m wind speed offshore of North Carolina - seasonal patterns

Abstract

Winds at 80 m elevation have been estimated with a stability-based height adjustment scheme to study the feasibility of utility-scale wind energy offshore of North Carolina. Data sources are the daily ASCAT 10 m wind field as measured by the METOP-A satellite, the North American Regional Reanalysis (NARR) estimates of near-surface atmospheric temperature, pressure and humidity and the National Climate Data Center's optimally-interpolated Advanced Very High Resolution Radiometer (AVHRR-OI) sea surface temperature (SST). The study focuses on the 2008-2012 time period. The COARE V3.0 algorithm is used to provide the stability-based height adjustment scheme. Data from six buoys have been used to establish validity of the remotely-sensed and modeled fields. A variety of results were produced, including long-term average wind speeds, wind power density and capacity factor at hub height, and a monthly climatology of these quantities. In this note the focus is on seasonal variations utilizing the monthly climatologies. Using the climatologies the largest differences between the neutral and stability-based schemes occur in winter and spring when and where stable atmospheric conditions are most common. There is a significant difference in the annual variation of atmospheric stability north and south of Cape Hatteras. Only the inner shelf region is prone to stable conditions during winter and spring south of Cape Hatteras, whereas the full width of the shelf is prone to stable conditions from fall into early summer north of Cape Hatteras. Where stable conditions occur the stability-based 80 m wind speeds are 2-3 m/s greater than 80 m neutral wind speeds, and where unstable conditions occur the stability-based 80 m wind speeds are 0.5-1 m/s less than the 80 m neutral wind speeds. The result is a pattern in the 80 m stability-based winds with notably greater speeds near the coastline than expected from a neutral height adjustment.