Key Features and Adverse Weather of the Named Subtropical Cyclones over the Southwestern South Atlantic Ocean

Abstract

This work documents the main features of six subtropical cyclones occurred between the years 2010 and 2016 over the southwestern South Atlantic Ocean, near the Brazilian coast, which received names (with the exception of one) from the Brazilian Navy Hydrographic Center. The fine-resolution ERA5 reanalysis and rainfall estimates from the Tropical Rainfall Measuring Mission (TRMM) were used to describe the synoptic environment and the adverse weather conditions during the six events. The support of a small-amplitude trough at mid-levels or a cut-off low, weak vertical wind shear, and moisture flux convergence are the main features contributing to the subtropical cyclogenesis at the surface. On the other hand, sea surface temperature (SST) presents a secondary contribution since the cyclones develop over the ocean with a wide range of SST values (from 22.5 °C to 28.6 °C in the initial phase of cyclones). The six subtropical cyclones are less deep in the atmosphere column than the tropical ones and, unlike the extratropical cyclones, they have little or no westward tilt with an increase in height. The studied subtropical cyclones produced adverse weather conditions such as (a) strong winds (reaching 17 m·s−1 at 10 m high) for a long period occurring east/southeastward of the cyclone center, and (b) high amounts of rainfall along the southeastern coast of Brazil, where the accumulated rainfall varied between 170 to 350 mm, being in most cases higher than the monthly climatology. Over the continent, the Brazilian states of Rio de Janeiro and Espírito Santo were the most affected by the intense rainfall associated with the cyclones.

Cyclogenesis and Density Currents in the Middle East and the Associated Dust Activity in September 2015

“…For instance, over North Africa it has been shown that a meandering polar jet can lead to a highly mobile subtropical jet (e.g., [57,58]) which in the presence of a mountainous barrier and an upper-level disturbance, such as a trough or a cut-off low as we have seen here, can trigger a surface cyclone south to the mountains [25]. A cut-off low has been also identified as a main feature contributing to cyclogenesis at the surface near the Brazilian coast (e.g., [59]). Here we show that this mechanism can also operate over arid areas that is, the Middle East with the difference that the cyclone we obtained here is dry and no precipitation was associated with it.…”

An Automatic Recognition Method for Airflow Field Structures of Convective Systems Based on Single Doppler Radar Data

“…The inverse of a convergence is a divergence. A cyclonic rotation [2] is defined as a circulation of winds around a central region of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. An anticyclonic rotation is defined as a circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.…”

Caracterização Da Zona De Convergência Do Atlântico Sul Em Campos Atmosféricos Recentes

“…A umidade que é transportada do oceano Atlântico Tropical para a região Norte do Brasil, em conjunto com a evapotranspiração da floresta Amazônica, além de contribuir para a precipitação em tal região, é em parte transportada para o Sul e Sudeste do Brasil pelos ventos a leste da Cordilheira dos Andes, conhecidos como Jatos de Baixos Níveis (JBN; SANTOS e REBOITA, 2019). Na região Sudeste, além da umidade proveniente da Amazônia, outra fonte de umidade é o oceano Atlântico Sul, uma vez que durante a estação chuvosa o Anticiclone Subtropical do Atlântico Sul (ASAS) encontra-se na sua posição mais a leste (REBOITA et al, 2018) propiciando o transporte de ar úmido do oceano para o continente (DRUMOND et al, 2008;REBOITA et al, 2018). Quadro et al (2012) ressalta a importância do ASAS no clima do Brasil, ao mencionar que somente o transporte de umidade da região Amazônica não seria suficiente para compor toda a umidade observada no Sul e Sudeste do Brasil no verão.…”

“…Tanto em Escobar e Costa 2005) e Escobar (2018, o padrão sinótico mais frequente da ocorrência de ZCAS indica que o ramo oceânico desse sistema se acopla a um ciclone. Embora a literatura não aborde expressamente a relação da ZCAS com os ciclones oceânicos, estudos recentes têm indicado a associação da umidade proveniente do continente com os ciclones formados na costa sudeste do Brasil, principalmente em eventos de ciclones subtropicais (GOZZO et al, 2017;REBOITA et al, 2018).…”