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Evaluating and Improving NWP Forecast Models for the Future: How the Needs of Offshore Wind Energy Can Point the Way

Abstract

Future needs of both the offshore wind-energy industry and NWP model improvement can be met with high-quality profile measurement arrays from new-generation remote sensors

To advance the understanding of meteorological processes in offshore coastal regions, the spatial variability of wind profiles must be characterized and uncertainties (errors) in NWP-model wind forecasts quantified. These gaps are especially critical for the new offshore wind-energy industry, where wind-profile measurements in the marine atmospheric layer spanned by wind-turbine rotor blades, generally 50–200 m above sea level (ASL), have been largely unavailable. Here, high-quality wind-profile measurements were available every 15 min from NOAA/ESRL’s High-Resolution Doppler Lidar (HRDL) during a month-long research cruise in the Gulf of Maine for the 2004 New England Air Quality Study. These measurements were compared with retrospective NWP-model wind forecasts over the area using two NOAA forecast-modeling systems (NAM and RAP). HRDL profile measurements quantified model errors, including their dependence on height above sea level, diurnal cycle, and forecast lead time. Typical model wind-speed errors were ~2.5 m s−1 and vector-wind errors, ~4 m s−1. Short-term forecast errors were larger near the surface—30% larger below 100 m than above, and largest for several hours after local midnight, biased low. Longer-term, 12-h forecasts had the largest errors after local sunset, biased high. At more than 3-h lead times, predictions from finer-resolution models exhibited larger errors. Horizontal variability of winds, measured as the ship traversed the Gulf, was significant and raised questions about whether modeled fields, which appeared smooth in comparison, were capturing this variability. If not, horizontal arrays of high-quality, vertical-profiling devices will be required for wind-energy resource assessment offshore. Such measurement arrays are also needed for improving NWP models.

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