@MastersThesis{Santos:2021:EsVaIo,
author = "Santos, Stella Pires de Moraes",
title = "Estudo da variabilidade ionosf{\'e}rica de baixas latitudes no
setor brasileiro durante eventos de feixes de vento solar de alta
velocidade",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2021",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2020-05-26",
keywords = "ionosfera, feixe r{\'a}pido de vento solar, regi{\~a}o de
intera{\c{c}}{\~a}o corrotante, tempestade geomagn{\'e}tica,
conte{\'u}do eletr{\^o}nico total, ionosphere, high-speed solar
wind streams, corotating interaction region, geomagnetic storm,
total electron content.",
abstract = "Neste trabalho apresenta-se um estudo do comportamento da
ionosfera de baixas latitudes no Brasil durante a fase inicial de
decl{\'{\i}}nio do ciclo solar 24 compreendendo os anos de 2016
e 2017. A fase decrescente do ciclo solar {\'e} caracterizada
pela redu{\c{c}}{\~a}o do n{\'u}mero de manchas solares e pelo
aparecimento gradual de regi{\~o}es denominadas buracos coronais.
Os buracos coronais s{\~a}o regi{\~o}es escuras, de baixa
densidade e campos magn{\'e}ticos abertos, de onde emanam feixes
de vento solar de alta velocidade, que ao se propagarem pelo
espa{\c{c}}o interplanet{\'a}rio interagem com feixes de vento
lento que os precederam criando uma regi{\~a}o de
intera{\c{c}}{\~a}o de feixes. Como os buracos corrotam com o
Sol, as vezes retornando em v{\'a}rias rota{\c{c}}{\~o}es
seguintes, tais regi{\~o}es s{\~a}o denominadas Regi{\~o}es de
Intera{\c{c}}{\~a}o Corrotante, ou CIRs (acr{\^o}nimo do
ingl{\^e}s, Corotating Interaction Regions). As CIRs se
caracterizam por regi{\~o}es de compress{\~a}o e
rarefa{\c{c}}{\~a}o do plasma, por campos magn{\'e}ticos
altamente oscilat{\'o}rios, devido a presen{\c{c}}a de ondas de
Alfv{\'e}n. Estes campos s{\~a}o os respons{\'a}veis por
tempestades geomagn{\'e}ticas quando sua componente sul se
reconecta com o campo geomagn{\'e}tico. Estas tempestades variam
na maioria das vezes entre fracas e moderadas, com poucos casos em
que a tempestade {\'e} intensa. As tempestades geomagn{\'e}ticas
associadas a este tipo de fen{\^o}meno, as quais s{\~a}o
estudadas nesse trabalho, afetam a ionosfera de baixas latitudes
de v{\'a}rias formas. Uma delas {\'e} a varia{\c{c}}{\~a}o do
Conte{\'u}do Eletr{\^o}nico Total Vertical, ou VTEC
(acr{\^o}nimo do ingl{\^e}s, Vertical Total Electron Content)
por v{\'a}rios dias ap{\'o}s o in{\'{\i}}cio da tempestade,
com intensifica{\c{c}}{\~o}es percentuais com
rela{\c{c}}{\~a}o aos cinco dias mais calmos t{\~a}o elevadas
quanto 400%, especialmente no per{\'{\i}}odo noturno. As causas
desta intensifica{\c{c}}{\~a}o s{\~a}o discutidas em termos de
campos el{\'e}tricos de penetra{\c{c}}{\~a}o, do
d{\'{\i}}namo perturbado e a poss{\'{\i}}vel
modifica{\c{c}}{\~a}o da atmosfera neutra. Al{\'e}m disto,
verifica-se a ocorr{\^e}ncia de irregularidades de plasma na
regi{\~a}o equatorial, denominadas Bolhas de plasma, ou spread-F
equatorial, o que pode ter sido influenciado por campos
el{\'e}tricos perturbados associados {\`a}s tempestades.
Tamb{\'e}m foi realizado um estudo estat{\'{\i}}stico da
resposta ionosf{\'e}rica no per{\'{\i}}odo mencionado,
atrav{\'e}s do VTEC, considerando-se majoritariamente as
tempestades moderadas, ou seja, utilizamos um filtro para o
|Sym-H|, onde: 50 nT \≤ |Sym-H| \≤ 110 nT e para
tempestades causadas apenas por CIRs/HSSs. As
varia{\c{c}}{\~o}es do VTEC em quatro esta{\c{c}}{\~o}es mais
representativas foram analisadas e verificou-se que as maiores
intensifica{\c{c}}{\~o}es ocorrem no per{\'{\i}}odo entre
18:00 e 04:00 LT (hora local), principalmente nas regi{\~o}es das
cristas da Anomalia Equatorial de Ioniza{\c{c}}{\~a}o, ou EIA
(acr{\^o}nimo do ingl{\^e}s, Equatorial Ionization Anomaly).
Este trabalho tem, portanto, potencial para contribuir com um
melhor entendimento sobre a influ{\^e}ncia do vento solar na
ionosfera de baixas latitudes, durante per{\'{\i}}odos de
atividade solar moderada bem como contribuir no desenvolvimento de
m{\'e}todos para previs{\~a}o de Clima Espacial. ABSTRACT: This
work presents a study of the behavior of the low latitude
ionosphere in Brazil during the descending phase of the solar
cycle 24 comprising the years 2016 and 2017. The descending phase
of the solar cycle is characterized by the decreasing number of
sunspots and the gradual appearance of regions defined as Coronal
Holes. Coronal Holes are dark regions of low-density and open
magnetic fields, from which High-Speed Solar Wind streams emanate.
As the solar wind streams propagate through interplanetary space,
they interact with slow wind streams that preceded them, creating
interaction regions. As the Coronal Holes corotate with the Sun,
sometimes returning for several subsequent rotations, as such
regions are defined as Corotating Interaction Regions or CIRs.
CIRs are characterized by regions of compression and rarefaction
of the plasma, and highly oscillatory magnetic fields, due to the
presence of Alfv{\'e}n waves. These fields are responsible for
geomagnetic storms after complex reconnection processes with the
geomagnetic field. These storms are usually weak to moderate with
few cases of intense storms. Geomagnetic storms associated with
this kind of solar events affect the low latitude ionosphere in
several ways. For instance, its observed a variation of the
Vertical Total Electron Content, VTEC, by several days after the
storm beginning, with intensifications as high as 400% in
comparison to the five quietest days VTEC, especially at night.
The sources of these intensifications are discussed in terms of
Prompt Penetration Electric Fields, PPEF, Disturbance Dynamo
Electric Fields, DDEF, and the possible modifications of the
neutral atmosphere. Also, there occur plasma irregularities over
the equatorial region, defined as Equatorial Plasma Bubbles, EPBs,
or Spread-Fs, which can be influenced by disturbed electric fields
associated with storms. A statistical study of the ionospheric
response using the parameter VTEC, was also carried out for the
analyzed period, considering mostly moderate storms, that is, we
use a filter for | Sym-H |, where: 50 nT \≤ | Sym-H |
\≤ 110 nT only for CIRs/HSSs driven storms. The variation
of the VTEC in four most representative sites was analyzed, and it
was found that the highest intensifications occur in the period
between 06:00 pm and 04:00 am LT (Local Time), mainly around the
regions at the crests of Equatorial Ionization Anomaly, EIA. In
this context, this work is of great interest for understanding the
influence of the solar wind on the low latitude ionosphere during
periods of moderate to low solar activity, as well as in the
development or improvement of methods for Space Weather
forecasting studies.",
committee = "Dal Lago, Alisson (presidente) and C{\^a}ndido, Cl{\'a}udia
Maria Nicoli (orientadora) and Guedes, F{\'a}bio Becker
(orientador) and Souza, Jonas Rodrigues de and Borges, Renato
Alves",
englishtitle = "Study of low latitude ionspheric variability over brazilian sector
during high speed solar wind streams events",
language = "pt",
pages = "148",
ibi = "8JMKD3MGP3W34R/42FDKFE",
url = "http://urlib.net/ibi/8JMKD3MGP3W34R/42FDKFE",
targetfile = "publicacao.pdf",
urlaccessdate = "25 abr. 2024"
}