@MastersThesis{Fernandes:1996:CaInRe,
author = "Fernandes, K{\'a}tia de {\'A}vila",
title = "Cavados invertidos na regi{\~a}o central da Am{\'e}rica do Sul",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "1996",
address = "Sao Jose dos Campos",
month = "1996-02-13",
keywords = "estudos do tempo e do clima, Am{\'e}rica do sul, ondas de leste,
cavados invertidos.",
abstract = "Cavados que se formam no escoamento de leste s{\~a}o ditos
invertidos. Exemplo cl{\'a}ssico de cavado invertido (CI)
s{\~a}o as ondas de leste. Os CIs que formam-se em latitudes
subtropicais e extratropicais da America do Sul ainda n{\~a}o
s{\~a}o bem entendidos. Uma climatologia de sua ocorr{\^e}ncia,
movimento e evolu{\c{c}}{\~a}o nas regi{\~o}es subtropicais da
Am{\'e}rica do Sul {\'e} obtida neste estudo. Cartas de
superf{\'{\i}}cie para um per{\'{\i}}odo de dez anos,
1980-1989, foram examinadas para estabelecer as
caracter{\'{\i}}sticas destes CIs. Um crit{\'e}rio baseado no
Laplaciano de press{\~a}o e usado para identificar os cavados nas
cartas de superf{\'{\i}}cie. A m{\'e}dia mensal de
ocorr{\^e}ncia de CIs mostra que eles s{\~a}o mais frequentes na
primavera e inicio do ver{\~a}o. Sobre a America do Sul, eles
apresentam-se, mais frequentemente, na faixa entre 15 a 25 graus S
no inverno e na faixa entre 20 a 35 graus S, no ver{\~a}o. Dois
tipos de situa{\c{c}}{\~a}o sin{\'o}tica s{\~a}o
identificadas: 1. CI ao norte de 20 graus S, nos ventos de leste
tropical, provavelmente associado com o aquecimento continental no
ver{\~a}o e 2. CI na parte norte do centro de anticiclones
migrat{\'o}rios na retaguarda de uma frente fria. Os eixos dos
cavados na superf{\'{\i}}cie, mostram na climatologia uma
prefer{\^e}ncia por inclina{\c{c}}{\~a}o no sentido NW-SE (45).
Entretanto um n{\'u}mero significante (26,9) mostra uma
orienta{\c{c}}{\~a}o meridional e o restante tem
orienta{\c{c}}{\~a}o NE-SW. A maioria dos CI n{\~a}o causam
condi{\c{c}}{\~o}es severas de tempo. Entretanto alguns poucos,
quando associados a advec{\c{c}}{\~a}o de vorticidade relativa
na media troposfera, evoluem para baixas fechadas no
Atl{\^a}ntico Sul na costa do Sul do Brasil. Alguns cavados nas
c{\'e}lulas de altas press{\~o}es frias, embora raramente,
causam neve nas regioes serranas do Sul do Brasil. A
evolu{\c{c}}{\~a}o temporal de quatro CIs, bastante distintos em
suas caracter{\'{\i}}sticas, s{\~a}o apresentadas como estudo
de casos com a ajuda de dados em pontos de grade analisados pelo
European Center for Medium Range Weather Forecasts (ECMWF). Os CIs
apresentam ciclo de vida de cerca de tres dias e uma escala
horizontal de 1000 Km. S{\~a}o bastante rasos, basicamente
limitados aos ventos de leste em baixos n{\'{\i}}veis. Uma
analise qualitativa do balan{\c{c}}o da equa{\c{c}}{\~a}o da
vorticidade relativa na regi{\~a}o central de um CI (03 de marco
de 1982) mostra que o termo de adveccao e tilting n{\~a}o
s{\~a}o importantes e que os termos de diverg{\^e}ncia e
advec{\c{c}}{\~a}o vertical contribuem para a ciclog{\^e}nese.
A tend{\^e}ncia de press{\~a}o a superf{\'{\i}}cie, baseada
nos campos de diverg{\^e}ncia revelam a defici{\^e}ncia dos
dados dispon{\'{\i}}veis. ABSTRACT: Troughs forming in the
easterlies are inverted. Classic examples of an inverted troughs
(IT) are the easterly waves observed and studies in the equarial
Pacific Ocean and the Caribean Sea. The ITs forming in the
subtropics and extratropics of South America are not yet well
understood. A climatology of their occurrence, movement and
evolution over the subtropics of South America is obtained in this
study. Daily surface synoptic charts for the 10 year period,
1980-89, are examined for establishing the characteristics of
these ITs. A criterion based on the Laplacian of the surface
pressure is used to identify the troughs on the surface charts.
The mean monthly frequency of the occurrence of the ITs shows that
they prefer the spring and early summer seasons. Over South
America they occur mostly in the 15 to 25 S latitudinal band in
winter and in the 25 to 35 S latitudinal band in summer. Two types
of synoptic situations are identified: 1. IT in the tropical
easterlies, probably associated with the continental heating in
summer and 2. IT in the northern part of large migratory
anticyclonic centers behind a large frontal boundary. The trough
lines of the surface ITs in this climatology have a predominantly
NW to SE orientation (45%). However a significant number (26,9%)
show a meridional orientation and the rest show a SW to NE
orientation. Most ITs do not cause severe weather conditions.
However, a few, when helped by the a.dvection of cyclonic
vorticity in the middle troposphere, grow into deep lows in the
South Atlantic off the coast of southern Brazil. Some troughs in
the cold extratropical high pressure cells, although rarely, cause
snowfall in the highlands of South Brazil. The temporal evolutions
of four ITs, each different from the other in its characteristics,
are presented as case studies with the help of the grid data
analysed by the European Center for Mediun-I-Range Weather
Forecasts (ECMWF). They present a life cycle of about three days
and a horizontal scale of 1000 km. They are very shallow,
basically limited to the shallow easterly flow heuristic analysis
of the vorticity budget in the central region of an IT (03 March
1982) shows that the horizontal advection and tilting terms are
unimportant and that the divergence and the vertical advection
terms contribute for the cyclogenesis. The surface pressure
tenclency analysis based on the divergence fields reveals the
deficiency, and poor quality of the available data.",
committee = "Cavalcanti, Iracema Fonseca de Albuquerque (presidente) and
Satyamurty, Prakki (orientador) and Gan, Manoel Alonso and
Ferreira, Nelson Jesus and Sugahara, Shigetoshi",
copyholder = "SID/SCD",
englishtitle = "x",
label = "7723",
language = "pt",
pages = "103",
ibi = "6qtX3pFwXQZ3r59YCT/GUnyd",
url = "http://urlib.net/ibi/6qtX3pFwXQZ3r59YCT/GUnyd",
targetfile = "publicacao.pdf",
urlaccessdate = "11 maio 2024"
}