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<p>This study analyzes a heavy rainfall event that affected the city of Rio de Janeiro (Brazil) between December 30 and 31, 2021. Two distinct rainfall peaks were identified: the first occurred between 18 UTC on December 30 and 00 UTC on December 31, when hourly totals exceeded 30&#xa0;mm at six rain gauges of the Alerta Rio system; the second took place between 03 and 07 UTC on December 31, with hourly accumulations not exceeding 5.4&#xa0;mm. Synoptic analysis revealed that the event was linked to a mid-level trough at 500&#xa0;hPa, which intensified in response to potential vorticity anomalies near 200&#xa0;hPa, generated by the intrusion of stratospheric air. Elevated ozone concentrations, reduced relative humidity, and increased temperatures corroborated the presence of these anomalies. The upper-level trough at 200&#xa0;hPa also enhanced mass divergence over Southeast Brazil, reinforcing the large-scale dynamic forcing. At lower levels, near 850&#xa0;hPa, moisture convergence combined with cyclonic vorticity at 500&#xa0;hPa, highlighting the combined influence of dynamic and thermodynamic factors in the development of deep convection and heavy rainfall. Regional-scale analysis further revealed that regions of intense upward vertical motion at 500&#xa0;hPa corresponded to low-level mass convergence at 850&#xa0;hPa and upper-level divergence at 250&#xa0;hPa. Thermodynamic indices, including the K index and Total Totals, exceeded 36&#xa0;°C and 45&#xa0;°C, respectively, confirming the presence of favorable atmospheric conditions for torrential rainfall.</p>

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Evaluation of a Heavy Rainfall Event in Rio de Janeiro City Associated with Upper-Air Instability Dynamically Forced by Stratospheric Air Intrusion

  • 期刊论文

  • 发表日期：

    2025年11月8日

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  • Uziel de Oliveira Coelho,
  • Fabricio Polifke da Silva,
  • Wanderson Luiz-Silva,
  • Fernanda Cerqueira Vasconcellos

摘要

This study analyzes a heavy rainfall event that affected the city of Rio de Janeiro (Brazil) between December 30 and 31, 2021. Two distinct rainfall peaks were identified: the first occurred between 18 UTC on December 30 and 00 UTC on December 31, when hourly totals exceeded 30 mm at six rain gauges of the Alerta Rio system; the second took place between 03 and 07 UTC on December 31, with hourly accumulations not exceeding 5.4 mm. Synoptic analysis revealed that the event was linked to a mid-level trough at 500 hPa, which intensified in response to potential vorticity anomalies near 200 hPa, generated by the intrusion of stratospheric air. Elevated ozone concentrations, reduced relative humidity, and increased temperatures corroborated the presence of these anomalies. The upper-level trough at 200 hPa also enhanced mass divergence over Southeast Brazil, reinforcing the large-scale dynamic forcing. At lower levels, near 850 hPa, moisture convergence combined with cyclonic vorticity at 500 hPa, highlighting the combined influence of dynamic and thermodynamic factors in the development of deep convection and heavy rainfall. Regional-scale analysis further revealed that regions of intense upward vertical motion at 500 hPa corresponded to low-level mass convergence at 850 hPa and upper-level divergence at 250 hPa. Thermodynamic indices, including the K index and Total Totals, exceeded 36 °C and 45 °C, respectively, confirming the presence of favorable atmospheric conditions for torrential rainfall.