Monday, 9 July 2012: 11:30 AM
Essex Center/South (Westin Copley Place)
The Alcântara Launch Center is the Brazilian space port and it is located at a coastline (Lat 02o19'03", Lon 44o22'06") downwind of a cliff 40-m high in the NE Brazil. The gases and particulate released during the launches are of concern, making the study of dispersion mandatory. The flow transition from open ocean past by the coastline generated an internal boundary layer (IBL) due to the roughness step (from smooth to rough surface) change and that cliff. The flow is mainly driven by the trade winds, although the interaction with land-sea circulation may not be negligible. These features modify the ocean wind profile as measured over land. One way to study dispersion is by means of wind tunnel simulation. Similarity criteria demand that the incoming flow profile (among other quantities) be similar to the observed wind ocean profile. We present preliminary results characterizing the wind profile, which would serve as input flow profile for dispersion studies. We analyzed observations of wind speed and direction collected between 1995 and 1999 by six aerovanes mounted in 70-m height tower standing about 200 m downwind of the cliff. To study the diurnal and annual patterns of the wind profile the stored mean values of 10 min were hourly and monthly and averaged. A simple estimate of the IBL height was carried out by assuming an incoming flat-profile flow and a dependence on the upwind distance of the shore as suggested by Pendergrass and Arya (1984). IBL height ranges from 30 to 40 m at tower location, being higher during the period of more intense turbulence (between 10 and 15 LT). The wind power-law profile above the IBL height shows an alpha exponent greater (up to 0.35) than those encountered in the literature (about 0.100.11) for open ocean wind profile. This result indicates that IBL height is probably greater and that the step change in the surface roughness cannot explain alone the observed profiles. Other causes such as temperature step change and the cliff elevation certainly play a role to be still addressed.
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