Surface level wind gusts and turbulence in the Alcantara Launch Center - Brazil

Brazilian rockets are launched from Alcântara Launch Center (ALC), whose location close to equator is privileged for launching of geosynchronous satellites. The nearest atmospheric layer from the surface is the one with high temporal and space variability. In addition, turbulence and sudden change of wind velocity may affect straightforward the rockets' structure as well as its trajectory. The geographic and topographic features around make the ALC a special case from the micrometeorological point of view, as it locates in the Atlantic Ocean seaboard nearby a cliff about 40-m high. Thus, the characterization of the surface boundary layer and, particularly, the internal boundary layer, is very important. We present data of wind turbulence and gusts collected for 10 days during the dry season in 2008. Synoptic conditions were fair weather with clear sky and no precipitation occurred during the whole field campaign. A set of 10 masts equipped with aerovanes (model 05103 from R.M. Young) was deployed to measure wind speed and direction at the sample rate of 0.5 Hz. Time series were averaged over 10-minutes time interval and stored in a data-logger CR-7 Campbell Scientific Instrument. Turbulence intensity (standard deviation over mean speed), gust factor (max speed over mean speed), and gust amplitude (maximum speed minus mean speed) were computed from the available dataset. Results show that the wind direction is predominant from ENE, with the mean vector wind direction of 60 degrees, in agreement with the Trades regime. The diurnal cycle of wind direction averaged over all aerovanes is strongly marked varying from 45 to 75 degrees and it has a peak value at about 1000 LST (-3hours). Both mean vector wind speed and mean vector wind direction are not symmetrically distributed about the mean value ; wind speed trends to be below the mean value (skewness = 0.51) and wind direction trends to be above the mean value (skewness = –0.45). The mean wind vector speed averaged over all days and over all aerovanes presents values ranging from 5.0 to 6.5 m/s. Minimum and maximum speed are about 3.0 and 9.0 m/s, respectively. Time series show that the gusts and turbulence are intensified between 0800 and 1300 LST, likely due to the interaction between the sea breeze and trade regime. Turbulence intensity, gust factor, and gust amplitude are strongly correlated to each other: their maximum values take place about 1000 LST. Turbulence intensity values are between 0.13 and 0.27, whereas gust factor and gust amplitude are between 1.3 and 1.8 m/s, and 2.2 and 4.3 m/s, respectively. Such a characterization of wind behavior and turbulence within the surface boundary layer is very important to guarantee the safety during rocket launchings from ALC.