Análise de tendências e fatores determinantes da intensificação de Sistemas Convectivos de Mesoescala e Linhas de Instabilidade na costa Norte-Nordeste da América do Sul

Abstract

The objective of this work was to determine the convective patterns and precipitation associated with the Mesoscale Convective Systems and Squall Lines on the North-Northeast coast of South America and investigate the main variations related to synoptic, regional and local factors. In addition, dynamic and thermodynamic variables were evaluated, as well as the possible factors responsible for their seasonal, interannual and daily variability and long-term trends. Brightness temperature data from satellites were used to evaluate the frequency and intensity of Mesoscale Convective Systems and Squall Lines during the period from 1998 to 2017. The identification and classification of Squall Lines followed a semi-objective method based on brightness temperature thresholds. The relationship with environmental conditions was assessed based on data from Reanalysis ERA5 and radiosondes carried out in the study area. Additionally, a composition analysis was performed to identify the variability patterns of Squall Lines of strong intensity and conditions without the occurrence of Squall Lines during years of ENSO. The profiles of potential equivalent temperature, zonal and southern wind speed and mixing ratio showed more pronounced differences during the month of April for El Niño conditions in the occurrence of strong Squall Line. As for long-term trends, changes in spatial patterns of air temperature and precipitation have occurred along the North-Northeast coast of South America in the past two decades. The tendency to increase the Sea Surface Temperature in the North Tropical Atlantic region was persistent and acted together with the dynamics and thermodynamics of the low atmosphere in favor of a higher occurrence of Mesoscale Convective Systems and Squall Lines. It was found that the most heated Sea Surface Temperature over the North Atlantic Tropical and Tropical Pacific oceans (this acting indirectly) favored the occurrence of intense Mesoscale Convective Systems and Squall Lines. This influence occurs due to the combined effect of the dynamic condition, associated with the Sea Surface Temperature patterns of the Tropical Pacific, and the thermodynamic condition, forced by the heating of the surface waters of the North Tropical Atlantic. These conditions are shown to be the favorable environment for the occurrence of intense events of Mesoscale Convective Systems and Squall Lines. There is a prospect that Mesoscale Convective Systems and Squall Lines will become more frequent and intense on the North-Northeast coast of South America if the conditions presented are maintained over the long term.