Linhas de instabilidade e trocas turbulentas na interface floresta amazônica-atmosfera

Abstract

Squall lines (SLs) are convective phenomena that frequently occur in the tropical atmosphere and have been widely investigated by the scientific community. In this work, high-frequency experimental data were collected at the Amazon Tall Tower Observatory (ATTO) site during two years, one of which was considered “normal” (2014) and the other was a year of strong El Niño (2015), and the satellite images of the central region of the Amazonia. The objective was to investigate whether there is influence in El Niño years on the number of occurrence of SLs and consequently on the impact that these phenomena exert on precipitation, temperature, relative humidity, radiation and turbulent fluxes calculated by the turbulent eddies correlation method. For this, the average daily cycles of these magnitudes were used for different seasons and years. The results showed an increase in the occurrence of SLs in El Niño years. It was noted that during the presence of SLs, the following occurred: 1) high precipitation rates (on average 11.5 mm per event) being higher in El Niño years; 2) temperature decay of 2 and 2.5°C in 2014 and 2015, respectively; 2) temperature decay of 2 and 2.5 °C in 2014 and 2015, respectively; 3) increase in wind speed by 1.5 and 2 m s⁻², in 2014 and 2015; 4) decrease in shortwave radiation by more than 50% in 2014 and more than 70% in 2015, caused by cloud cover that reduced the passage of radiation; and 5) increase in relative humidity, being higher in the El Niño year. Regarding turbulent fluxes, there was a decrease of 35 W m⁻² in 2014 and 25 W m⁻² in 2015 in the sensible heat flux, and 90 W m⁻² in latent heat in the two years at the time of the SLs occurrence and the momentum flux presented values 3 times greater than the values registered hours before the occurrence of SL. The CO2 flux, on the other hand, had a increase of 13 and 22 μmol m⁻² s⁻¹ in 2014 and 2015, respectively, at the time of the occurrence of SLs due to the decrease in incident radiation, which impacted on the photosynthetic rates of plants. It is believed that these results are important, since the transport of water vapor and CO2 and consequently the hydrological and CO2 cycles can be altered by the presence of SLs and the occurrence of the El Niño. Consequently, in a scenario of climate change, where El Niños and SLs are expected to be more frequent, people's quality of life can be compromised.