Simulações de linhas de instabilidade continentais e a formação de correntes de densidade superficiais ricas em ozônio

Abstract

The main objective of this work is to better understand the increase of ozone (O3) in the surface by influence of density currents formed by the cold air of the downdrafts coming from mesoscale convective systems, using data measured in Central Amazonia, at the Manacapuru experimental site of the GoAmazon project (Observations and Modeling of the Green Ocean Amazon), reanalysis of the ECMWF Era-Interim (European Center for Medium-Range Weather Forecasts) and numerical simulations of the atmosphere with the Brazilian Regional Atmospheric Modeling System (BRAMS) model, version 5.3. To investigate surface O3 increases, the data measured in Manacapuru and ECMWF Era-Interim reanalysis were used first. Through these data, between April 10 and 14, 2014, an O3 "plume" located in the middle troposphere was observed, together with the increase in the concentrations of this gas at the surface. The images of the satellite in the infrared channel referring to this period were analyzed, and the images of the day 04/14 showed the passage of two lines of instability (LIs) by Manacapuru, the first passed at dawn and the second in the afternoon. It was observed that these LIs did not form on the North / Northeast coast of South America by the action of the sea breeze, as it commonly occurs. We then used the analysis of surface synoptic charts to understand the formation of these convective systems, and these have suggested that LIs developed within the continent, influenced by a Frontal System that reached south-eastern South America during this period. Thus, these LIs were called the Continental Instability Lines (LICONs). The experimental data measured near the surface were then examined on 04/14, and it was found that during the passage of the LICONs there were strong downdrafts in Manacapuru, since high precipitation rates and increases in the horizontal wind velocity were observed, as well as increases in atmospheric pressure, air density and surface O3 levels. Additionally, there were also sharp declines in the potential equivalent temperature values and the mixing ratio. Numerical simulations using the JULES-CCATT-BRAMS model were used to understand the three-dimensional structure of the chemistry and thermodynamics of the atmosphere during the passage of these LICONs. The simulations were able to capture the main chemical and thermodynamic characteristics of the atmosphere during the presence of the first LICON observed at dawn on 04/14. The simulation results showed that downdrafts from LICON bring cooler, drier, dense air to the surface. This downdrafts air column passed by the O3 “plume" in the middle troposphere, formed rich gas density currents and low level jets were induced near the surface and spread the O3. Finally, this cleaner air column reduced surface carbon monoxide (CO) levels, and higher O3 levels were responsible for the increase in surface nitrogen dioxide (NO2).