Low atmosphere flow at the Alcântara Space Center

The atmospheric flow, in the region where the main Brazilian Space Launching Center (CLA) is located at Alcântara, MA, Brazil, is influenced by strong trade winds ( > 5 m s-1) and surface contrasts. The CLA is located near the equator (2 19' 10'' S) right at the coastal line. The coast at that region has complex contour. It is surrounded by water at northwest (NW), north (N), east (E), and southeast (SE). The water body in the NW and N represents a small branch of the ocean projecting southwest (SW) inland, while the area in the south (S) is a major bay and in the east is the Atlantic Ocean. The fact that CLA is near the equator, with strong trade winds, and with complex coastal contour, makes it a unique site in terms of thermal induced circulations cases (e. g. sea–land breezes) already studied. So far, only one or two aspects together, of the three above mentioned, have been investigated. For instance a series of works done for Kennedy Space Center at Cape Canaveral in Florida have dealt with the issue of complex coastal region and moderate-strong background flows, but away from the equator. Oliveira and Fitzjarrald (1993) have investigated the land-river breezes in a river delta region, near the equator in the Amazon, but with no strong background flows. Thus, the objective of the present work is to characterize the local flow and to determine to what extend the local thermal contrasts affect the local circulation. To do such we analyze several years of radiosonde data taken at CLA, plus surroundings onshore and offshore locations, and wind measurements taken by a 70 m tall tower at the region. The results indicate that the convective boundary layer (CBL) is typically 600 m deep, and the wind direction within it is predominantly from NE. The advection of the marine boundary layer (MBL) inland guarantees a quasi-steady inversion height for the CBL, as far as 7 km inland. The winds within the boundary layer (BL) and just above it show 24-hours cycles. From midnight to noon, the BL wind seems to increase and rotate clockwise, while in afternoon to late evening it seems to decrease and rotate counterclockwise. Above the boundary layer between 1000 m and 1500m, the wind shows almost an opposite behavior but with a smaller rotation. The entire rotations, for BL and above it, are about 45 degrees or less around NE, showing no reversal in the flow direction. It is likely that any horizontal pressure gradient resulting from the thermal contrast between land and sea is not strong enough or do not have component anti-parallel strong enough to cancel or overcome the trade winds.