Diurnal Cycle of the Coastline Winds Profile Within the Surface Layer in the Alcântara Launch Center

The wind profile inside the surface layer has been studied at the Alcantara Space Center (ASC), located at the north part of northeast Brazil (2°S), right at the coastal line of Atlantic Ocean. The atmospheric flow is influenced by strong trade winds and surface contrasts (sea-continent). The InterTropical Convergence Zone is the dominant meteorological features and the zonal component (associated with the trade winds) is higher than the meridional wind (associated with the sea breeze). The objective of this study is to investigate if a sea breeze develops and whether its counterpart can be identified by the surface wind profile. This mesoscale circulation is embedded with the large scale trade winds pattern. The dataset used was obtained from continuous measurements with a mini wind profiler 4000 model (Atmospheric Science Corporation, Santa Clarita, CA, US) from surface up to 200 m ( 5 m height interval) from 90 days (March up to June), which corresponds the end of the wet season and transition to the dry period. Measurements of the atmospheric stability were made using an eddy correlation instrument (CSAT3A from Campbell Scientific Instrument, Logan, UT, US) in order to split the wind profiles within stratification classes. However, due to the high winds (surface winds are higher than 6-7 m/s most of the time) the neutral conditions are predominant more than 95% of the time. Consequently, the wind profile obeys the logarithmic law validating the Monin-Obhukov theory. The windspeed (WS) varies from approximately 4.0 m/s at 30 m height (minimum level of measurements) up to 9.0 m/s at the top layers (heights between 180-200 m). There is clearly a diurnal cycle of the WS being the strong winds occurring (within the whole layer) between 9 up to 14 local time (LT). For instance, at 50 m height the typical nighttime WS values are in the range 4.0 – 5.0 m/s, increasing it to 5.5 – 6.0 m/s at daytime. For 100 m height, this difference is from 7.0-7.5 m/s for nocturnal period and in the range 7.5-8.0 m/s for daytime. The wind direction (WD) is very persistent and constant within the layer showing a diurnal rotation: at late morning (9 – 11 LT) the WD is 67 degrees, rotating it to 57 degrees at 21-23 LT. Although this is a small difference, this northward shift is associated with intensification of the meridional component of the wind, associated with the terrestrial counterpart of the sea breeze developed due to the surface contrast.