Five-day Cycle of the Surface Wind in the Alcântara Launch Center During the Dry Quarter

3. Departamento de Controle do Espaço Aéreo, Centro Integrado de Meteorologia Aeronáutica, Rio de Janeiro, RJ, Brazil

Abstract: The Alcântara Launch Center (Centro de Lançamento de Alcântara, CLA) is the main launch site for the Brazilian aerospace vehicles and located on the northern coast of Northeast Brazil. The 5-day cycle (C5d) is a variability in the 3-9 days band that is found in the surface wind data at CLA during the dry quarter (September to November). This study aimed to characterize C5d and find out the main atmospheric factors related to the C5d phases, VMAX (VMIN), which contains the more intense (weaker) winds. Surface wind data measured at CLA and ERA-Interim reanalysis data for the dry quarter over the course of 9 years – 1996-1999, 2005, 2012-2015 – were used. Wavelet transform was applied to the observed data to obtain C5d features, while reanalysis data for a number of cases were used to obtain the average large-scale factors related to C5d phases. Results showed that C5d period is concentrated around 5 days, C5d occurs frequently and its active periods occur in about 1/3 of dry quarter days. The distribution of wind speed and direction for C5d phases showed that, from VMAX to VMIN, the surface wind over CLA weakens (reduction from 9-12 m/s to 9-6 m/s) and rotates counterclockwise (from ENE to NE direction). To obtain the distinct features between the C5d phases, 35 cases that represent typical cases of C5d during active periods were analyzed. Results showed that, from VMAX to VMIN, the South Atlantic Subtropical High (SASH) weakens or propagates eastwards for all cases, while the North Atlantic Subtropical High (NASH) weakens or propagates northwards for about 3/4 of cases. Therefore, SASH could be regarded as the main driver of C5d, while NASH could be considered as an important complementary forcing of C5d.