@PhDThesis{Arraut:2007:AsGeDi,
author = "Arraut, Josefina Moraes",
title = "Frentes e frontog{\^e}nese no ver{\~a}o: aspectos
geom{\'e}tricos, din{\^a}micos e impactos sobre as chuvas nos
subtr{\'o}picos da Am{\'e}rica do Sul",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2007",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2007-10-18",
keywords = "METEOROLOGIA, Frentes, Ver{\~a}o, Frontog{\^e}nese, Chuva,
Transporte de umidade, Am{\'e}rica do Sul, Sela, Separatrizes,
Press{\~a}o, METEOROLOGY, Fronts, Summer, Frontogenesis,
Rainfall, Humidity transport, South america, Saddle, Separatrices,
Pressure.",
abstract = "Este trabalho apresenta tr{\^e}s estudos relacionados {\`a}s
caracter{\'{\i}}sticas e causas das chuvas nos subtr{\'o}picos
da Am{\'e}rica do Sul (AS) e do padr{\~a}o continental de
transporte de umidade no ver{\~a}o. O primeiro estudo tem um
ponto de vista climatol{\'o}gico. Revela que, pela extens{\~a}o
da costa norte da AS at{\'e} a regi{\~a}o norte do Brasil,
ingressa umidade vinda principalmente do Atl{\^a}ntico tropical
norte. Por outro lado, a maior parte da umidade que deixa aquela
regi{\~a}o oceanica dirige-se ao interior da AS, entrando por
esta faixa da costa. Nos subtr{\'o}picos e extra-tr{\'o}picos, a
distribui{\c{c}}{\~a}o espacial do desvio padrao di{\'a}rio
climatol{\'o}gico da componente meridional do transporte de
umidade {\'e} notoriamente semelhante {\`a} do pr{\'o}prio
m{\'o}dulo desta componente; ela {\'e} tamb{\'e}m semelhante ao
padr{\~a}o climatol{\'o}gico de chuvas, indicando que tanto o
transporte de umidade quanto as chuvas recebem importante
contribui{\c{c}}{\~a}o de dist{\'u}rbios transientes. O segundo
estudo traz novidades sobre a maneira como a Baixa do Noroeste da
Argentina (BNOA) interage com cavados transientes ao sul. A
associa{\c{c}}{\~a}o entre estes elementos define uma estrutura
geom{\'e}trica que se forma no campo de press{\~a}o. Neste
estudo mostra-se como esta estrutura influencia os campos de
ventos e de transporte de umidade. Um dos elementos importantes
desta estrutura {\'e} uma sela que ocorre obrigatoriamente entre
a BNOA e o cavado transiente. Esta sela {\'e} um local
preferencial de converg{\^e}ncia e deforma{\c{c}}{\~a}o dos
ventos, advec{\c{c}}{\~o}es quente e fria, frontogenese em
temperatura potencial equivalente e chuvas. O restante da
estrutura pode ser bem resumida pela geometria e
localiza{\c{c}}{\~a}o geogr{\'a}fica das separatrizes desta
sela. Ambas se estendem desde os tr{\'o}picos at{\'e} as
latitudes m{\'e}dias, intersectando-se na sela que {\'e} situada
nos subtr{\'o}picos. A dire{\c{c}}{\~a}o e o sentido das
{\'o}rbitas que compoem estas separatrizes indicam a
dire{\c{c}}{\~a}o e o sentido do escoamento do vento que,
portanto se aproxima desde os tr{\'o}picos e das latitudes
m{\'e}dias at{\'e} a vizinhan{\c{c}}a da sela. Duas das
{\'o}rbitas que localmente compoem estas separatrizes
indentificam-se longe da sela em uma auto-liga{\c{c}}{\~a}o que
cont{\'e}m a BNOA no seu interior. Isto permite a
forma{\c{c}}{\~a}o de um prolongamento do cavado transiente
envolvendo a auto-liga{\c{c}}{\~a}o, batizado aqui de
L{\'{\i}}ngua de Baixa Pressao a Leste dos Andes (LBPLA). A
LBPLA for{\c{c}}a geostroficamente a forma{\c{c}}{\~a}o de um
corredor de umidade desde a Amazonia at{\'e} as latitudes
m{\'e}dias, permitindo que o vapor de {\'a}gua que passou pela
floresta alimente o dist{\'u}rbio transiente. Ilustra-se
tamb{\'e}m como, na ausencia da auto-liga{\c{c}}{\~a}o, a
geometria do campo de ventos determina que o dist{\'u}rbio
transiente seja alimentado por umidade vinda diretamente do
Atlantico Sul. Prop{\~o}e-se que esta {\'u}ltima
configura{\c{c}}{\~a}o geom{\'e}trica seja t{\'{\i}}pica do
inverno. Encontra-se que a estrutura geom{\'e}trica brevemente
descrita acima {\'e} muito frequente no ver{\~a}o mas nem sempre
d{\'a} or{\'{\i}}gem {\`a}a frontogenese ou chuvas.
Identificam-se eventos organizados de frontogenese e chuva
fortemente influenciados por esta estrutura, com
dura{\c{c}}{\~a}o de alguns dias. Sua ocorrencia est{\'a}
associada {\`a} incurs{\~a}o de dist{\'u}rbios transientes
vindos do Pac{\'{\i}}fico. Estes eventos s{\~a}o classificados
em duas categorias, que podem ser distinguidas pelo deslocamento
da frontogenese: para nordeste (eventos NE) e para o leste
(eventos LE). Ambas s{\~a}o estudadas atrav{\'e}s de compostos e
tem sua estrutura resumida em modelos conceituais. As
diferen{\c{c}}as estruturais entre as duas categorias s{\~a}o
causadas por comportamentos distintos dos dist{\'u}rbios
transientes nos altos n{\'{\i}}veis. O {\'u}ltimo estudo {\'e}
uma avalia{\c{c}}{\~a}o estat{\'{\i}}stica da
associa{\c{c}}{\~a}o entre a sela da LBPLA e a frontogenese nos
subtr{\'o}picos da Am{\'e}rica do Sul. Mostra-se que a
presen{\c{c}}a desta sela favorece a frontogenese e quanto mais
alta a frontogenese, maior a presen{\c{c}}a estat{\'{\i}}stica
da sela, tendendo a 100% para frontogenese muito elevada.
Mostra-se tamb{\'e}m uma associa{\c{c}}{\~a}o
estat{\'{\i}}stica entre a ocorrencia da sela sobre o
centro-norte da Argentina e chuva ligeiramente a nordeste. A chuva
{\'e} m{\'a}xima um dia ap{\'o}s a ocorrencia da sela.
Associa{\c{c}}{\~a}o an{\'a}loga {\'e} encontrada entre
frontogenese intensa e chuva nas mesmas regioes. ABSTRACT: Three
different aspects related to summer precipitation over subtropical
South America (SA) and the continental pattern of humidity
transport in that season are studied. Firstly, a climatological
point of view is adopted and it is shown that most of the humidity
that enters SA through its northern coast, up to ParŽa, comes from
the tropical Northern Atlantic. It is also shown that most of the
humidity that leaves that part of the ocean heads towards inland
SA, crossing over this coast. In the subtropics and extra-tropics,
the spatial distributions of the climatological daily standard
deviation of the meridional humidity transport and of its
magnitude are notoriously similar to each other, as well as to
that of the climatological rains. This points towards an important
contribution from transient disturbances to the rain and humidity
transport patterns. In the following part of the work, some new
aspects pertaining the interaction between the North Western
Argentinean Low (NAL) and transient troughs south of it are
brought to light. The combination of these two elements brings
about the formation of a geometrical structure in the pressure
field. The influence of this structure over the wind field is
documented and explained. One of the important elements of this
structure is the saddle that necessarily occurs between the NAL
and the transient trough. This saddle is a preferred spot for
convergence and deformation of the wind field, both warm and cold
advections, frontogenesis in equivalent potential temperature and
rain. In addition to this saddle, the shape and geographical
location of its separatrices reveal the essential aspects of the
referred structure. Both extend from the tropics to the
midlatitudes, intersecting themselves on the saddle point, which
is located in the subtropics. The flow over the orbits that make
up these separatrices reflects the flow of the wind, which
therefore aproaches the saddle both from the tropics and from the
midlatitudes. Two of the orbits which locally make up the
separatrices merge away from the saddle forming a self connection
of the saddle which contains the NAL in its interior. This allows
for the formation of an extension of the transient trough, which
wraps over the self connection, and is here called the Low
Pressure Tongue East of the Andes (LPTEA). The LPTEA
geostrophically forces the development of a moisture corridor all
the way from Amazonia to the midlatitudes, allowing the water
vapour which has flowed over the forest to fuel the transient
disturbance. It is ilustrated how, in the absence of a saddle self
connection, the geometry of the wind field causes the transient
disturbance to be fuelled by humidity coming directly from the
South Atlantic. This is probably the typical winter situation. It
is found that the geometrical structure described above is very
common during summer, but does not always lead to frontogenesis
and rain formation. Organized events, lasting a few days, in which
frontogenesis and rain formation are strongly influenced by this
structure are identified. Their occurence is associated with the
incursion of transient disturbances coming from the Pacific. These
events are separated in two categories, which can be distinguished
by the displacement of the frontogenesis: towards the northeast
(NE events) and towards the east (LE events). Both are studied
through composits and have their basic structure described in
conceptual models. The structural differences between the two
categories are caused by the behaviour of the transient
disturbance in the high levels. In the last part of the work, the
link between the Low Pressure Tongue and its saddle and
frontogenesis over the subtropics of SA is statistically
evaluated. It is shown that the saddle favours frontogenesis.
Furthermore, the presence of the saddle becomes more statistically
likely the higher the frontogenesis, approaching 100% for very
high values. A statistical link is also shown to exist between the
occurrence of the saddle over northern central Argentina and rain
slightly to the northeast. The rain attains maximum intensity one
day after the detection of the saddle. A similar link is found
between intense frontogenesis and rain over the same regions.",
committee = "Nobre, Carlos Afonso (presidente) and Bonatti, Jos{\'e} Paulo
(orientador) and Satyamurty, Prakki and Marques, Valdo da Silva
and Marques, Rosa de F{\'a}tima Cruz",
copyholder = "SID/SCD",
englishtitle = "Fronts and frontogenesis during summer: geometrical and dynamical
aspects and the influence over rainfall on the South American
subtropics",
language = "pt",
pages = "175",
ibi = "6qtX3pFwXQZGivnK2Y/SvaAB",
url = "http://urlib.net/ibi/6qtX3pFwXQZGivnK2Y/SvaAB",
targetfile = "paginadeacesso.html",
urlaccessdate = "03 maio 2024"
}