Estudo da dependência dos parâmetros de identificação do meandro do vento com o acoplamento na camada limite atmosférica noturna

Abstract

The stable boundary layer (CLE) begins to develop after the sunset, when short-wave radiation from the Sun ceases and the Earth’s surface ceases to heat, in these conditions, due to the great radioactive loss of the earth’s surface, turbulence intensity is reduced by several orders of magnitude, in a regime with these characteristics the vertical levels are energetically decoupled. During one night, alternations can occur between intervals in which vertical levels are energetically decoupled and times when there is a large turbulent mixture, the transition between these two states occurs at a specific value of wind speed. In low turbulence regimes, which is a characteristic of a state of vertical energy decoupling, the flow near the surface is governed by phenomena of larger scales, such as submeso scales, among which we can mention the phenomenon of meander of the horizontal components of the wind, which is characterized by oscillation of the horizontal direction of the wind. The meander of the winds plays a fundamental role in the diffusion of scalars cite anfossi2005, in addition, most dispersion models fail to represent the influence of the meander, mainly because the meander of the winds is not yet fully understood and characterized, highlighting the relevance of this work, whose research theme is “Study of the dependence of the wind meander identification parameters with the coupling in the atmospheric nocturnal boundary layer” and has as objective to relate the state of atmospheric coupling with the occurrence of winds meander, using the velocity required for the coupling as the initial criterion for wind meander identification. For this, data from the experiment Fluxes Over Snow-covered Surfaces II (FLOSSII) will be submitted to two methods for the identification of meander characteristic parameters, the first being the adjustment of the autocorrelation of the data to the Autocorrelation Function (ACF) through of the loop parameter (m) and the meander period (T*) and the second the Hilbert-Huang Transform (HHT) using the marginal spectrum for meander period determination (T*). With the characteristic meander parameters, a statistical analysis will be performed using the classical criterion of weak wind (Ū > 1,5 ms-1 ) and the coupling speed (Ūcoup) to find one hour intervals in which there is the possibility of meander occurrence. Comparing the two criteria, the analyses performed show that the Ūcoup criterion found approximately 4 times more intervals, maintaining the same percentage of cases of possible meander, especially for the higher measurement levels. In sites that have high-level measurement towers, the criterion of Ū < 1,5 ms-1 may restrict most cases, while the coupling speed causes the natural separation of flow regimes. Thus allowing all possible cases to be analysed.