@PhDThesis{Oliveira:2019:ExTrSu,
author = "Oliveira, J{\'e}ssica Tatiane da Silva",
title = "Extratropical transition of subtropical cyclones over southwestern
Atlantic Ocean",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2019",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2019-02-28",
keywords = "Subtropical cyclones, extratropical transition, Potential
Vorticity Inversion, ciclones subtropicais, transi{\c{c}}{\~a}o
extratropical, Invers{\~a}o da Vorticidade Potencial.",
abstract = "Subtropical cyclones that often develop over the southern coast of
Brazil can significantly impact agriculture, transport and the
day-to-day lives of the population. However, there is a lack of
studies regarding these weather systems that is of scientific and
operational interest. The goal of the current study is to improve
the knowledge of the dynamical processes related to subtropical
cyclones undergoing extratropical transition (SCET) and to
identify the main associated mechanisms for this process. To
achieve this purpose, a climatological analysis of the SCET over
the Southwestern Atlantic Ocean was developed. 47 SCET were
identified during the austral summer (November- March) in the
1985-2015 period. An annual mean of 1.6 SCET per year with
standard deviation of 1.3 was found. The monthly distribution of
these systems showed that the months with higher SCET frequency
were January, February and December, respectively. The main
features of the structure of SCET are investigated using composite
analysis of meteorological fields. The results indicate that SCET
are associated with the intrusion of upper level Potential
Vorticity (PV) and the propagation of cyclonic systems at the rear
of the SCET. Also, the low level temperature advection plays a key
role in the extratropical transition (ET) of these systems. A case
study is presented to illustrate SCET pattern and investigate the
impacts of PV anomalies in its life cycle. A case study was
analyzed using as reference the cyclone Anita, which developed
near the southeastern coast of Brazil in March 2010. The
potentially significant anomalies of PV during the ET are
identified through the PV inversion method. The results confirm
the intrusion of an upper tropospheric PV anomaly during the
pre-transitioning stage of Anita. However, the lower level PV
anomalies are also found to be of great importance at the ET time.
Numerical experiments with the regional model WRF (Weather
Research and Forecasting) indicate that the lower level PV
anomalies were fundamental to the ET of Anita. On the other hand,
although the upper tropospheric PV anomaly impacts significantly
the propagation and intensity of Anita, its absence did not
prevent the ET occurrence. Sensitivity test suggests that the
interaction of Anita with a shallow extratropical cyclone prior to
the ET was not the primary mechanism to the transitioning process,
but impact the time and position of its occurrence, contributing
to prevent the re-intensification of Anita. RESUMO: Os ciclones
subtropicais que tipicamente ocorrem nas proximidades da costa sul
do Brasil impactam significativamente os meios de transporte,
agricultura e o dia a dia da popula{\c{c}}{\~a}o. Apesar disso,
existem poucos estudos abordando essa tem{\'a}tica de grande
interesse cient{\'{\i}}fico e operacional. Este estudo visa
aprimorar o conhecimento da din{\^a}mica dos ciclones
subtropicais que passam por transi{\c{c}}{\~a}o extratropical
(CSTE) e identificar os mecanismos fundamentais para
ocorr{\^e}ncia desse processo. Para tal, uma an{\'a}lise da
climatologia dos CSTE sobre o Oceano Atl{\^a}ntico Sudoeste foi
elaborada. 47 CSTE foram identificados durante o ver{\~a}o
austral (Novembro-Mar{\c{c}}o) durante o per{\'{\i}}odo de
1985-2015. Desse modo, foi encontrada uma m{\'e}dia de 1,6 CSTE
por ano, com desvio padr{\~a}o de 1,3. A distribui{\c{c}}{\~a}o
mensal desses sistemas mostrou que os meses com maior
freq{\"u}{\^e}ncia de CSTE foram Janeiro, Fevereiro e Dezembro,
respectivamente. A estrutura dos CSTE foi investigada atrav{\'e}s
da an{\'a}lise de composi{\c{c}}{\~o}es. Os resultados indicam
que os CSTE est{\~a}o associados com a intrus{\~a}o de anomalia
de Vorticidade Potencial (VP) de altos n{\'{\i}}veis e com a
propaga{\c{c}}{\~a}o de um sistema cicl{\^o}nico na retaguarda
do CSTE. Al{\'e}m disso, a advec{\c{c}}{\~a}o de temperatura na
troposfera inferior desempenha um papel importante no processo de
transi{\c{c}}{\~a}o extratropical (TE) desses sistemas. Um
estudo de caso {\'e} apresentado para ilustrar os CSTE e para
investigar os impactos das anomalias de VP durante o ciclo de vida
desses sistemas. O ciclone escolhido para esse estudo de caso foi
o Anita, que se desenvolveu pr{\'o}ximo a costa sudeste do Brasil
em Mar{\c{c}}o de 2010. As anomalias de VP potencialmente
significantes para a TE foram identificadas atrav{\'e}s do
m{\'e}todo da Invers{\~a}o da Vorticidade Potencial. Os
resultados confirmaram a intrus{\~a}o de uma anomalia de VP na
alta troposfera durante o est{\'a}gio
pr{\'e}-transi{\c{c}}{\~a}o do Anita. No entanto, as anomalias
de VP de baixos n{\'{\i}}veis desempenham um papel importante
durante a TE. Experimentos num{\'e}ricos com o modelo WRF
(WeatherResearchandForecasting, sigla em ingl{\^e}s) indicaram
que a anomalia de VP de baixos n{\'{\i}}veis {\'e} fundamental
para a TE do Anita. Por outro lado, embora as anomalias de VP na
alta troposfera influenciem significativamente a
propaga{\c{c}}{\~a}o e intensidade do Anita, a aus{\^e}ncia
delas n{\~a}o impediu a ocorr{\^e}ncia de TE. Testes de
sensibilidade sugerem que a intera{\c{c}}{\~a}o do Anita com um
ciclone extratropical fraco no per{\'{\i}}odo que antecede a TE,
n{\~a}o foi o principal mecanismo para o processo de
transi{\c{c}}{\~a}o, mas impactou o tempo e a
posi{\c{c}}{\~a}o em que a transi{\c{c}}{\~a}o ocorreu,
contribuindo para que a n{\~a}o re-intensifica{\c{c}}{\~a}o do
Anita.",
committee = "Gan, Manoel Alonso (presidente) and Ferreira, Nelson Jesuz
(orientador) and Hodges, Kevin Ivan (orientador) and Coutinho,
Mariane Mendes and Pereira Filho, Augusto Jos{\'e} and Yamazaki,
Toshihiro",
englishtitle = "Transi{\c{c}}{\~a}o extratropical de ciclones subtropicais sobre
o Oceano Atl{\^a}ntico Sudoeste",
language = "en",
pages = "156",
ibi = "8JMKD3MGP3W34R/3SQM9DS",
url = "http://urlib.net/ibi/8JMKD3MGP3W34R/3SQM9DS",
targetfile = "publicacao.pdf",
urlaccessdate = "28 mar. 2024"
}