Análise climatológica da refratividade atmosférica na região da Ilha de Trindade

Abstract

The Brazilian coastal region has an intense maritime traffic, composed by several types of ships. In order toguarantee navigation safety, such vessels are equipped with communication and detection equipment, radios andradars, and the performance of these equipment is strongly influenced by propagation of electromagneticconditions in the atmosphere. This propagation is associated to refractive conditions in the layers near the surfaceof the sea which, in turn, depends on the vertical distribution of the water vapor and temperature in the air. Theobjective of this study is to evaluate the atmospheric refractivity conditions, using the modified refractivity index(M), as described by Oliveira Jr et al. (2005). Therefore, a previous climatology of the vertical profile M, in theperiod from 2006 to 2016, and the variability of propagation profile conditions were analyzed in function ofdifferent synoptic situations. Vertical profiles of M were calculated using the daily radio soundings informationfrom the meteorological station of Trindade Island (-20o50'; -29o31'). For the whole period, 10 cases wereclassified as superrefraction condition, 2991 as standard condition and only 1 as subrefraction. During theanalysis, it was verified that values of M classified as normal or superrefraction were associated with a markedvertical gradient of specific humidity and mixing ratio. In the superrefraction episodes, it was also verified thepresence of high pressure systems, favoring the intensification of the upward movements and, thus, inhibiting thecontribution of humidity to higher levels of the atmosphere.