Um estudo da fusão de células convectivas e a geração de fenômenos de tempo severo no centro-sul do Brasil

• Ano de defesa: 2026
• Autor(a) principal: Santana, Rafael José Claros
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Santa Maria; Brasil; UFSM; Programa de Pós-Graduação em Meteorologia; Centro de Ciências Naturais e Exatas
• Palavras-chave em Português: Fusões de células convectivas; Supercélula; Ocorrências de tempo severo; Nudger; Convective cell mergers; Supercell; Severe weather hazards; CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::METEOROLOGIA
• Link de acesso: http://repositorio.ufsm.br/handle/1/39231

The southeastern region of South America is highly prone to severe storms due to environments characterized by strong vertical wind shear combined with the persistent low-tropospheric meridional transport of warm, moist air from the Amazon Basin. This setup leads to the genesis of distinct severe weather hazards, including convective wind gusts, large hail, and tornadoes. Because convective storms often develop in close proximity to one another, interactions such as convective cell mergers are favored. Recent studies have increasingly linked these mergers to the intensification of severe weather events. Consequently, understanding the mechanisms and typologies of cell mergers is of paramount importance. This study presents a quantitative statistical analysis to assess the correlation between cell mergers and significant severe weather reports, specifically convective windstorms ( 100 km h -1 ≥ ), significant hail (≥ 4 cm), and supercellular tornadoes. Six distinct types of convective interactions were identified: (1) mergers of unicells and multicells with supercélulas; (2) mergers of unicells and multicells with squall lines; (3) mergers of unicells/multicells with other unicells/multicells; (4) mergers of unicells/multicells resulting in a supercell; (5) mergers of supercells with other supercells; (6) the interaction of nudger cells with supercells. The latter does not constitute a complete merger, but rather an interaction where unicells, multicells, or supercells couple with the rear flank of a primary supercell, acting as a dynamical catalyst. Furthermore, the interactions were quantified based on their physical nature as either constructive or destructive, and correlated with the severe weather reports. Qualitative analyses of each interaction type suggest that cell mergers often enhance storm severity; for instance, nudger cells tend to intensify the rear-flank downdraft (RFD) of primary supercells, thereby facilitating tornadogenesis. Finally, a case study of a tornadic event in Concórdia, Santa Catarina, on June 22, 2022, was conducted to evaluate the role of a secondary supercell acting as a catalyst (nudger) for the tornado-producing supercell downstream.