Jatos de baixos níveis na Camada Limite Noturna Amazônica e Sua Influência no Transporte de Escalares

Abstract

This work is a long-term study aimed at investigating the structure of the turbulent flow during the occurrence of Low Level Jets (LLJs) in the Nocturnal Boundary Layer (NBL) in Central Amazonia. The experimental data for this work came from the ATTO (Amazon Tall Tower Observatory) project, which has micrometeorological sensors installed on two towers, one 80m high and the other 325m high. These towers collect data on temperature, wind speed components (u, v and w), gases (H2O and CO2), among others. The data used in this study was collected from July 2021 to January 2022. This data was used to identify the presence of LLJ’s in the Amazonian NBL. Descriptive statistics were carried out on the parameters of height, direction and wind speed for the events detected. After detecting the LLJ events during the period studied, a classification of events into LLJ’s with a signal and LLJ’s without a signal was implemented, based on their impacts at the level of the forest canopy. Seven events from each class were separated to obtain dimensionless and composite profiles of momentum and sensible heat fluxes, temperature, wind speed, turbulent kinetic energy, as well as H2O and CO2 concentrations. A number of 132 LLJ events were detected, with July having the highest number of events. The average parameters of the LLJ's are: height of 130m, direction of the 30.39ºand a wind speed of 3.6m/s. As for the effects of the presence of LLJ’s, it can be seen that the LLJ class with a signal promotes intense wind shear, which increases the fluxes of momentum and sensible heat and doubles the turbulent kinetic energy during its occurrence. It can be concluded that the height of the Night Boundary Layer and the Residual Layer, as well as the characteristics of the topography of the ATTO site, directly interfere with the parameters and formation of LLJ’ss in the region. In addition, there is an indication that there is a dimensionless speed threshold for the action of the LLJ to promote downward mixing.