Climatology and trends of severe storm environments in subtropical South America
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Data
2024-02-27Primeiro coorientador
Allen, John Terrence
Primeiro membro da banca
Anabor, Vagner
Segundo membro da banca
Ferraz, Simone Erotildes Teleginski
Terceiro membro da banca
Reboita, Michelle Simões
Quarto membro da banca
Salio, Paola Veronica
Metadata
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Severe storms produce hazardous weather phenomena, such as large hail, damaging winds,
and tornadoes. However, relationships between convective parameters and confirmed severe
weather occurrences are poorly quantified in south-central Brazil. This study explores hail,
damaging wind, and tornado reports sourced from the PREVOTS project from June 2018 to
December 2021. Measurements of convectively-induced wind gusts from 1996 to 2019 are obtained
from METAR reports and the INMET operational network of automated weather stations.
Convective parameters were computed from ERA5 reanalysis and used to perform a discriminant
analysis using mixed-layer CAPE and shear (0-6 km, DLS). Compared to other regions,
thermodynamic parameters associated with severe weather episodes exhibit lower magnitudes
in south-central Brazil. DLS performs better in distinguishing different types of hazardous
weather, although it struggles to discriminate between distinct severity levels. Five discriminants
were evaluated to address the sensitivity of the discriminant analysis to distinct environmental
regimes and hazard types. These include discriminants for any severe storm, severe hail
only, severe wind gust only, and all environments categorized into high and low CAPE regimes.
The best performance was found for the high CAPE regime, followed by the severe wind. All
discriminants demonstrate that DLS plays a more important role in conditioning severe storm
environments in Brazil, confirming the need to ensure that parameters and discriminants are
tuned to local severe weather conditions. By applying one of the discriminants (high CAPE)
as a proxy for severe storm environments in subtropical South America, a climatology of the
frequency of these environments from 1980 to 2021 was developed. The two primary regions
of severe storm environments are the Andes foothills and Sierras de Cordoba in Argentina and
the triple border (Argentina-Brazil-Paraguay). Seasonally, the warm season stands out, with
the Argentinean hotspot in summer and the triple border in spring. The diurnal hotspot in Argentina
exhibits higher frequencies during mid-afternoon, and the triple border presents a higher
frequency overnight. Concerning trends, severe storm environment frequency decreases considerably
over the hotspot region in Argentina and in the northernmost part of the domain in Brazil.
This reduction is primarily driven by the decrease in MLCAPE. Seasonally, trends are negative
in Argentinas hotspot throughout all seasons. Conversely, increasingly favorable conditions for severe storms are observed during summer across the Argentina/Uruguay border and, in spring,
in the triple border. The consistent drop in severe storm environments in Argentina is related
to the reduction of MLCAPE. In summer and spring, the positive but not significant trend of
MLCAPE in areas with a robust increase in DLS determines the increase in severe storm environments.
Concerning interannual variability, El Niño years present more hours favorable to
deep convection, whereas La Niña and Neutral years a reduced number compared to the climatology.
The primary factor contributing to variations in severe storm environments across
different ENSO phases is MLCAPE.
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