On the predominance of unstable atmospheric conditions in the marine boundary layer offshore of the U.S. northeastern coast

This paper reports on research that looked at wind data collected offshore along the Northeast Unitied States. The paper's main finding is that atmospheric conditions around Cape Wind are predominantly turbulent, or unstable, which is very different from prevailing data from European offshore wind farms in the Baltic Sea and the North Sea. Wind conditions at Cape Wind were shown to be unstable between 40 and 80 percent of the time, depending on season and time of day, The abstract of the paper is provided below. The full paper can be accessed from the links on this page.


The marine boundary layer of the northeastern U.S. is studied with focus on wind speed, atmospheric stability, and turbulent kinetic energy (TKE), the three most relevant properties in the context of offshore wind power development.

Two long-term observational data sets are analyzed. The first one consists of multilevel meteorological variables measured up to 60 m during 2003–2011 at the offshore Cape Wind tower, located near the center of the Nantucket Sound. The second data set comes from the 2013–2014 IMPOWR campaign (Improving the Modeling and Prediction of Offshore Wind Resources), in which wind and wave data were collected with new instruments on the Cape Wind platform, in addition to meteorological data measured during 19 flight missions offshore of New York, Connecticut, Rhode Island, and Massachusetts.

It is found that, in this region: (1) the offshore wind resource is remarkable, with monthly average wind speeds at 60 m exceeding 7 m s1 all year round, highest winds in winter (10.1 m s1 ) and lowest in summer (7.1 m s1 ), and a distinct diurnal modulation, especially in summer; (2) the marine boundary layer is predominantly unstable (61% unstable vs. 21% neutral vs. 18% stable), meaning that mixing is strong, heat fluxes are positive, and the wind speed profile is often nonlogarithmic (~40% of the time); and (3) the shape of the wind speed profile (log versus nonlog) is an effective qualitative proxy for atmospheric stability, whereas TKE alone is not.

Archer Et Al 2016 Journal Of Geophysical Research Atmospheres

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Source: http://onlinelibrary.wiley....

JUL 18 2016
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