Controles exercidos pelo vento médio e pela turbulência nos fluxos e gradientes verticais de escalares na camada limite atmosférica

Abstract

In the present work, the control that the average wind and turbulence exert on the air temperature, concentrations of water vapour, carbon dioxide (CO2) and methane (CH4) in the atmospheric boundary layer is studied. The goal is to understand whether gradients and vertical fluxes of scalars respond differently to mean wind variations. A multi-resolution spectral decomposition is used to address how the patterns found depend on their timescale and wind speed. In addition, the vertical gradients of the scalars measured at different heights in the atmosphere, the terms of the turbulent flux budget equations and covariances between temperature and scalars have also been analyzed in relation to the mean wind speed. Aiming at understanding the behavior of these scalars, this study was developed in three different regions, covering landscapes that experience the intensification of greenhouse gas emissions, located in the Southeast and South of Brazil. In the southeast, the experimental site is located in the city of Linhares - ES, close to a thermoelectric plant and to the ocean. In this experimental site, the study period comprised 9 nights, of which two of them were a case study. There was consistent wind decay throughout this period, with a stable boundary layer corresponding to the transition from weak to very stable regime. In the south, the experimental sites are on the Pampa biome, one of them is located in the city of Aceguá in a grassland with cattle and the other site is located in the city of Cachoeira do Sul in the middle of an irrigated rice field. In these experimental sites, the period comprises 21 and 18 days, respectively, of which both the night and day periods were studied. Descending sensible heat, ascending CO2 and CH4 fluxes were consistently observed at night, regardless of the stable boundary layer regime. Ascending fluxes of latent heat were observed in the region where there was a water layer and of both signs in the other regions. Sensible and latent heat fluxes are positively related to mean wind speed. The same does not happen with gas fluxes, which increase up to a certain wind speed and then decay.