Análise de estruturas coerentes na camada superficial estável em Candiota, RS, através da função intermitência
AbstractCoherent structures of the ramplike kind were observed in Superficial Boundary Layer’s measurements at Candiota site, under stable stratification conditions. To establish their characteristics, micrometeorological data obtained on 4 measurement campaigns, which happen on July, 1994, and February, May, and November, 1995, were analyzed. Data was measured at a 12 m tower, with a sonic anemometer, a thin wire thermometer, a Kripton hygrometer, and two Gill anemometers. The temporal series were submitted to a quality control method, which selected 255 files, making up a total of almost 49 hours of data. To identify coherent structures on temporal series of temperature and humidity fluctuation, the conditional sampling technique named intermittent function was applied. The frequency distribution of coherent structures’ duration detected on the temperature and humidity series during the four periods are of the exponential type, typical of flat terrain. For temperature, the most frequent interval of the frequency distribution during winter is of 10 to 14.3 s, while, in the other seasons, the most frequent interval is of 14.3 to 18.6 s. Other characteristics were also evaluated, such as the number of structures every 20 minutes, which is around 25; the intermittent factor, which represents the time occupied by the structures, and it is of 60%; the intensity of the structures, which is between 0.2 and 0.3 ºC for temperature and of 0.13 and 0.23 g/kg for humidity; and the contribution of those structures to sensible and latent heat , which is of around 45% for the former and 60% for the later. Since intensity of coherent structures in temperature series decreases with the stability parameter, the coherent structures of ramplike kind might be merged with the smaller scale turbulence in the region near neutrality. The influence of the tower and instruments on the characteristics of the coherent structures was also evaluate, and it was determined that they cause no significant interference.
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