Investigation of Approaching Ocean Flow and its Interaction with Land Internal Boundary Layer

The Alcântara Launch Center is located near the Brazilian Northeastern coastline downwind of a cliff 40 m high. Furthermore, the flow transition fro m open ocean past by the coastline generated an internal boundary layer (IBL) due to the roughness step change. The flow is main ly driven by the Trades, although the interaction with land-sea circulat ion may not be negligible. These features modify the ocean wind ocean profile as measured over land at the coastal site. We present here an ongoing research aiming to characterize the wind profile, wh ich would serve as input flow profile in wind tunnel experiments and for gas dispersion studies. We analyzed the data of wind speed and direction collected between 1995 and 1999 by six aerovanes mounted in a 70-m height tower located about 200 m downwind the cliff. To study the diurnal and annual patterns of the wind profile the stored mean values of 10 min were monthly and hourly averaged. A simple estimate of the IBL height by assuming a dependence on the upwind distance of the shore as suggested in the literature were carried out. IBL height ranges from 30 to 40 m at tower location and being higher between 10 and 15 Local Time (LT). The wind profile power-la w shows an alpha exponent greater (up to 0.35) than those encountered in the literature (about 0.10-0.11) for open ocean wind profile. The step change in the surface roughness cannot alone exp lain such a change in the alpha exponent. Other causes such as temperature step change and the cliff elevation certainly p lay a ro le to be still addressed.