@MastersThesis{Ribeiro:2014:ClSiFr,
author = "Ribeiro, Bruno Zanetti",
title = "Climatologia sin{\'o}tica das frentes quentes no Sudeste da
Am{\'e}rica do Sul",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2014",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2014-02-26",
keywords = "frente quente, climatologia sin{\'o}tica, compostos, modelagem
num{\'e}rica, instabilidade termodin{\^a}mica, warm front,
synoptic climatology, composites, numerical modeling,
thermodynamic instability.",
abstract = "Sistemas frontais ocorrem frequentemente nas latitudes
subtropicais da Am{\'e}rica do Sul, tendo um grande impacto
nessas regi{\~o}es. Isso tem motivado muitos estudos sobre
frentes, a grande maioria sobre frentes frias. Pesquisas sobre
sistemas frontais em n{\'{\i}}vel global mostraram que o Sudeste
da Am{\'e}rica do Sul sofre uma grande influ{\^e}ncia
tamb{\'e}m de frentes quentes, as quais foram pouco estudadas
nesse continente. A car{\^e}ncia de estudos mais abrangentes
sobre frentes quentes motivou o presente estudo. Utilizaram-se
dados das rean{\'a}lises do CFSR/NCEP para identificar os eventos
de frentes quentes no per{\'{\i}}odo de 1979 a 2010, no Sudeste
da Am{\'e}rica do Sul entre \$20^{º}S\$ e \$35^{º}S\$,
atrav{\'e}s de um m{\'e}todo objetivo baseado nos campos de
vento e na magnitude do gradiente meridional de temperatura
potencial equivalente (\$\theta\$\$_{e}\$) em 850 hPa. Foram
elaborados compostos de algumas vari{\'a}veis atmosf{\'e}ricas
desde os dois dias que antecedem a ocorr{\^e}ncia das frentes
quentes at{\'e} os dois dias que a sucedem. Dois casos foram
simulados com o modelo regional Eta/CPTEC para analisar as
caracter{\'{\i}}sticas de mesoescala. Foram contabilizadas 809
frentes quentes no per{\'{\i}}odo estudado, sendo que a maior
parte esteve relacionada {\`a} forma{\c{c}}{\~a}o de ciclones
extratropicais na Bacia do Prata e ao retrocesso de frentes
estacion{\'a}rias. A maioria dos casos ocorreram no inverno
(36\%), sendo o ver{\~a}o a esta{\c{c}}{\~a}o com menor
n{\'u}mero de frentes quentes (12,8\%). Os compostos e suas
anomalias em rela{\c{c}}{\~a}o {\`a} m{\'e}dia mostraram que
as frentes quentes se formaram, em m{\'e}dia, associadas {\`a}
borda leste da Baixa do Chaco, entre o Sul do Paraguai, Nordeste
da Argentina e Oeste da regi{\~a}o Sul do Brasil. O escoamento de
norte/noroeste, associado {\`a} a{\c{c}}{\~a}o do Jato de
Baixos N{\'{\i}}veis da Am{\'e}rica do Sul, e o avan{\c{c}}o
de uma massa de ar frio de sul aumentam o gradiente de
\$\theta\$\$_{e}\$ na regi{\~a}o, sendo fatores
frontogen{\'e}ticos. Nos n{\'{\i}}veis superiores da troposfera
ocorre o avan{\c{c}}o de uma onda sin{\'o}tica de oeste, e a
forma{\c{c}}{\~a}o da frente quente em superf{\'{\i}}cie
{\'e} acompanhada pela intensifica{\c{c}}{\~a}o de uma crista
de altura geopotencial em altos e m{\'e}dios n{\'{\i}}veis. A
frente quente tem um deslocamento para sul/sudeste, precedendo, na
maioria dos casos, a forma{\c{c}}{\~a}o de sistemas de baixa
press{\~a}o no Oceano Atl{\^a}ntico adjacente ao Sudeste da
Am{\'e}rica do Sul. Compostos de precipita{\c{c}}{\~a}o
indicaram que o dia posterior {\`a} forma{\c{c}}{\~a}o da
frente quente {\'e} o mais chuvoso na regi{\~a}o, o que {\'e}
explicado pelo aumento dos {\'{\i}}ndices de instabilidade
termodin{\^a}mica ap{\'o}s a passagem do sistema frontal. As
simula{\c{c}}{\~o}es num{\'e}ricas efetuadas com o modelo
Eta/CPTEC mostraram algumas diferen{\c{c}}as entre as frentes
quentes de inverno e de ver{\~a}o. A identifica{\c{c}}{\~a}o do
sistema no inverno {\'e} mais clara, pois esta
esta{\c{c}}{\~a}o do ano apresenta menores varia{\c{c}}{\~o}es
locais dos gradientes de \$\ theta\$\$_{e}\$. No ver{\~a}o
ocorreu a forma{\c{c}}{\~a}o de sistemas convectivos nas
proximidades da frente quente, principalmente na retaguarda desta,
enquanto que no inverno a frente causou pouca nebulosidade. Tanto
no ver{\~a}o quanto no inverno formaram-se ondas ap{\'o}s a
passagem das frentes, as quais estavam associadas a instabilidade
termodin{\^a}mica elevada. ABSTRACT: Frontal systems occur
frequently in the subtropics of South America, having a great
impact in these regions. This has motivated many studies on
fronts, the vast majority are on cold fronts. Research on frontal
systems globally showed that the Southeastern South America
undergoes a great influence of warm fronts also, which have been
little studied in this continent. The lack of more comprehensive
studies on warm fronts motivated this study. Data from CFSR/NCEP
reanalysis were used to identify warm fronts events from 1979 to
2010, in Southeastern South America between \$20^{º}\$ S and
\$35^{º}\$S, by a method based on the wind field and the
equivalent potential temperature (\$\theta\$\$_{e}\$)
meridional gradient magnitude at 850 hPa. Composites of some
atmospheric variables were constructed since two days preceding
the occurrence of warm fronts until the days following. Two cases
were simulated with the regional Eta/CPTEC model in order to
analyze the mesoscale characteristics. 809 warm fronts were
accounted during the studied period, most of them was related to
the formation of extratropical cyclones in the La Plata Basin and
the retreat of stationary fronts. Most cases occurred in winter
(36\%), summer being the season with fewer warm fronts (12.8\%).
The composites and their anomalies in relation to the mean showed
that warm fronts formed, on average, in association with the
eastern edge of the Chaco Low, between the Southern Paraguay,
Northeastern Argentina and West of Southern Brazil. The flow from
north/northwest, associated with the South American Low Level Jet,
and the advance of a cold air mass from the south increases the
gradient of \$\theta\$\$_{e}\$ in the region, being
frontogenetic factors. On upper levels of the troposphere a
synoptic wave advances from the west, and the formation of the
surface warm front is accompanied by the intensification of a
geopotential height ridge at upper and middle levels. The warm
front has a displacement to south/southeast, preceding, in most
cases, the formation of low pressure systems in the Atlantic Ocean
adjacent to Southeastern South America. Composites of
precipitation indicated that the day after warm front formations
is the most rainy in the region, which is explained by the
increase of thermodynamic instability indexes after frontal system
passage. The numerical simulations performed with Eta/CPTEC model
showed some differences between winter and summer warm fronts.
System identification in winter is clearer, because this season
has lower local variations of \$\theta\$\$_{e}\$ gradients.
In summer occurred the formation of convective systems near the
warm front, especially in the rearward of the system, while in the
winter the front caused few cloudiness. Both in summer and winter
waves formed after the fronts passage, which were associated with
elevated thermodynamic instability.",
committee = "Satyamurty, Prakki (presidente) and Seluchi, Marcelo Enrique
(orientador) and Dereczynski, Claudine Pereira",
englishtitle = "Synoptic climatology of warm fronts in Southeastern South
America",
language = "pt",
pages = "171",
ibi = "8JMKD3MGP8W/3FL69TE",
url = "http://urlib.net/ibi/8JMKD3MGP8W/3FL69TE",
targetfile = "publicacao.pdf",
urlaccessdate = "03 maio 2024"
}