Escalas temporais do transporte turbulento em um sítio micrometeorológico no bioma Caatinga

Abstract

Turbulence is the primary mechanism for scalar transport in the lower troposphere, often posing a challenge for its study, particularly when its intensity is low and flows depend on sporadic turbulence occurrences and non-turbulent scale mechanisms. This makes estimates of surface exchanges quite imprecise. In the turbulent vortex covariance method, a time window of 30 minutes is commonly used for averaging; however, this window may not be suitable under strongly stable conditions. Therefore, selecting an appropriate time window for estimates is crucial to achieve satisfactory results. Understanding turbulence scales and their influence on the total flux is of great importance. For temporal scale studies using the Harr wavelet transform, it is necessary to decompose series of length 2n into series of different resolutions. This enables the identification of spectra and co-spectra associated with the variance and covariance of the series at different resolutions, revealing various temporal scales and their contributions to total transport. This study observed that turbulent transport temporal scales exhibit different behaviors based on the time of day, turbulence intensity varying between day and night, and flow regimes. With the reduction of turbulence temporal scales under strongly stable atmospheric conditions, spectral and co-spectral peaks show higher values compared to weakly stable nights, where turbulence is well-developed, and the turbulent scale dominates surface transports. It's also evident that submeso scales play a significant role in surface fluxes, especially under low turbulence intensity conditions.