@PhDThesis{Silva:2021:MoDrRa,
author = "Silva, Graziela Belmira Dias da",
title = "Modeling dropouts of radiation belt electrons driven by corotating
interaction regions during weak to moderate geomagnetic storms",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2021",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2021-05-14",
keywords = "Earth’s radiation belts, relativistic electrons, flux dropouts,
radial diffusion, ULF waves, cintur{\~o}es de
radia{\c{c}}{\~a}o da Terra, el{\'e}trons
relativ{\'{\i}}sticos, decr{\'e}scimos de fluxo, difus{\~a}o
radial, ondas ULF.",
abstract = "The Earths outer radiation belt hosts very dynamic populations of
relativistic and ultrarelativistic electrons trapped by the
geomagnetic field. Flux dropouts are common variations observed in
these electron populations, which can occur after solar wind
drivers hit the magnetosphere, such as corotating interaction
regions (CIRs). Currently, observational evidence indicates that
CIRs promote rapid dropouts produced by magnetopause shadowing and
outward radial diffusion mechanisms. However, it is still
necessary to investigate the role of these two dynamic mechanisms
through modeling. To quantify the contribution of each of them to
loss processes in the outer belt triggered by CIRs passages close
to Earth, this work extensively investigated three cases that
occurred during weak to moderate magnetic storms in 2017, at the
end of NASA Van Allen Probes era. This period was concomitant with
the declining phase of solar cycle 24 between 2016 and 2018. A
catalog of CIRs that includes the chosen case studies was produced
for this interval. Two of the selected events had solar wind
parameters varying at similar values in the CIRs, such as the flow
speed (400 to \& 600 km/s), dynamic pressure (. 15 nPa) and
density (. 40 cm\−3). As a result, the magnetopause was
similarly compressed in both cases to 7RE using the model of Shue
et al. (1998), or to 8RE as simulated with a global
magnetohydrodynamic (MHD) model. However, the electron dropouts in
the two events differed significantly in intensity and in the
affected L shells. From the calculation of the analytical radial
diffusion coefficients using MHD simulations, it was found that
the strongest and deepest dropout was related to more intense
diffusion rates inside the magnetopause during the storm time.
This result was validated by comparisons of the calculated
diffusion rates with observed radial diffusion coefficients
obtained from in-situ measurements of ultra-low frequency waves.
Also, the last closed drift shell (LCDS) calculated with the TS04
magnetosphere model showed that the effect of magnetopause
compression reached L = 5.5 in the most intense dropout event, and
L = 6 for the least intense dropout. Radial diffusion simulations
of these events were run for relativistic populations, using as
inputs the analytical diffusion coefficients (to simulate outward
radial diffusion), a loss term defined outside the LCDS (to
simulate magnetopause shadowing) and a variable condition at the
outer boundary (L = 6), obtained from calibrated phase space
densities measured by GOES-15. The simulated phase space densities
are comparable to the phase space densities observed by the Van
Allen Probes, so that the significant differences between the two
dropouts were reproduced. Simulations of radial diffusion effects
were also performed for the third case, although using only the
radial diffusion coefficients estimated from empirical models. In
this case, however, the simulations overestimated the phase space
densities during the dropout by factors up to 100. This
significant error throughout L < 6 is attributed to an invalid
approximation in L of the outer boundary condition during the
shadowing losses and to substorm injections in this dynamic
condition. The results obtained through the 1D diffusion modeling
for the analyzed events show that magnetopause shadowing and
outward radial diffusion are potential loss mechanisms for
generating dropouts during CIR-magnetosphere couplings, even in
periods of weak to moderate storms. RESUMO: O cintur{\~a}o de
radia{\c{c}}{\~a}o externo da Terra hospeda
popula{\c{c}}{\~o}es muito din{\^a}micas de el{\'e}trons
relativ{\'{\i}}sticos e ultrarelativ{\'{\i}}sticos
aprisionados pelo campo geomagn{\'e}tico. Decr{\'e}scimos de
fluxo (dropouts) s{\~a}o varia{\c{c}}{\~o}es comuns observadas
nessas popula{\c{c}}{\~o}es de el{\'e}trons, as quais podem
ocorrer ap{\'o}s a passagem pela magnetosfera de estruturas do
vento solar, tais como regi{\~o}es corrotantes de
intera{\c{c}}{\~a}o (CIRs). Atualmente, evid{\^e}ncias
observacionais indicam que as CIRs promovem r{\'a}pidos dropouts
pela magnetopausa, por meio dos mecanismos de compress{\~a}o da
magnetopausa e difus{\~a}o radial para fora do cintur{\~a}o. No
entanto, ainda {\'e} necess{\'a}rio investigar o papel desses
dois mecanismos din{\^a}micos por meio de modelagem. Para
quantificar a contribui{\c{c}}{\~a}o de cada um deles em
processos de perda no cintur{\~a}o externo desencadeados por
passagens de CIRs pr{\'o}ximas da Terra, este trabalho investigou
extensivamente tr{\^e}s casos ocorridos durante tempestades
magn{\'e}ticas fracas a moderadas em 2017, no final da era das
sondas Van Allen da NASA. Este per{\'{\i}}odo foi concomitante
com a fase de decl{\'{\i}}nio do ciclo solar 24 entre 2016 e
2018. Um cat{\'a}logo de CIRs que inclui os estudos de caso
abordados foi produzido para este intervalo. Dois desses eventos
escolhidos tiveram par{\^a}metros do vento solar variando em
valores semelhantes nas CIRs, tais como a velocidade de
pr{\'o}tons (400 a > 600 km/s), press{\~a}o din{\^a}mica (. 15
nPa) e densidade (. 40 cm\−3). Como resultado, a
magnetopausa foi comprimida de forma semelhante nos dois casos
para 7RE usando o modelo de Shue et al. (1998), ou para 8RE de
acordo com estimativa de um modelo magnetohidrodin{\^a}mico
global (MHD). No entanto, as perdas de el{\'e}trons nos dois
eventos diferiram significativamente em intensidade e nas camadas
L afetadas. A partir do c{\'a}lculo dos coeficientes de
difus{\~a}o radial anal{\'{\i}}ticos utilizando
simula{\c{c}}{\~o}es MHD, constatou-se que o dropout mais forte
e profundo esteve relacionado a taxas de difus{\~a}o mais
intensas na magnetosfera durante o per{\'{\i}}odo da tempestade
magn{\'e}tica. Esse resultado foi validado por
compara{\c{c}}{\~o}es dessas taxas de simula{\c{c}}{\~a}o com
observa{\c{c}}{\~o}es de taxas de difus{\~a}o calculadas com
medidas in situ de ondas de frequ{\^e}ncia ultra baixa.
Tamb{\'e}m, o par{\^a}metro que determina a {\'u}ltima
{\'o}rbita fechada dos el{\'e}trons (LCDS, last closed drift
shell), calculado com o modelo da magnetosfera TS04 mostrou que o
efeito da compress{\~a}o da magnetopausa atingiu L = 5, 5 no
evento de dropout mais intenso e L = 6 para o caso menos intenso.
Simula{\c{c}}{\~o}es de difus{\~a}o radial desses eventos foram
feitas para popula{\c{c}}{\~o}es relativ{\'{\i}}sticas, usando
como entradas os coeficientes de difus{\~a}o anal{\'{\i}}ticos
(para simular perdas por difus{\~a}o radial), um termo de perda
externo ao LCDS (para simular perdas diretas pela magnetopausa) e
uma condi{\c{c}}{\~a}o vari{\'a}vel no limite mais externo da
simula{\c{c}}{\~a}o (L = 6), obtida por medidas calibradas da
fun{\c{c}}{\~a}o de distribui{\c{c}}{\~a}o de el{\'e}trons
feitas pelo GOES-15. As densidades no espa{\c{c}}o de fase
simuladas s{\~a}o compar{\'a}veis {\`a}s densidades no
espa{\c{c}}o de fase observadas pelas Sondas Van Allen, de forma
que as significativas diferen{\c{c}}as dos dois dropouts foram
reproduzidas. Simula{\c{c}}{\~o}es de efeitos por difus{\~a}o
radial tamb{\'e}m foram feitas para um terceiro caso, usando
apenas os coeficientes de difus{\~a}o radial estimados a partir
de modelos emp{\'{\i}}ricos. Nesse caso, por{\'e}m, as
simula{\c{c}}{\~o}es superestimaram a fun{\c{c}}{\~a}o de
distribui{\c{c}}{\~a}o durante o dropout por fatores de at{\'e}
100. Esse erro significativo {\'e} atribu{\'{\i}}do a efeitos
secund{\'a}rios observados na condi{\c{c}}{\~a}o din{\^a}mica
utilizada em L = 6. Os resultados obtidos atrav{\'e}s da
simula{\c{c}}{\~a}o 1D de difus{\~a}o radial para os eventos
analisados mostram que a compress{\~a}o da magnetopausa e o
mecanismo de difus{\~a}o radial para fora da magnetosfera
s{\~a}o processos potenciais para gera{\c{c}}{\~a}o de dropouts
durante acoplamentos CIR-magnetosfera, mesmo em per{\'{\i}}odos
de tempestades fracas a moderadas.",
committee = "Wrasse, Cristiano Max (presidente) and Alves, L{\'{\i}}via
Ribeiro (orientadora) and Padilha, Antonio Lopes (orientador) and
Tu, Weichao (orientador) and Souza, Vitor Moura Cardoso e Silva
and Cerda, Rodrigo Andr{\'e}s Miranda and Rojas, Fl{\'a}via Reis
Cardoso",
englishtitle = "Modelagem de dropouts de el{\'e}trons do cintur{\~a}o de
radia{\c{c}}{\~a}o externo impulsionados por regi{\~o}es
corrotantes de intera{\c{c}}{\~a}o durante tempestades
geomagn{\'e}ticas fracas a moderadas",
language = "en",
pages = "188",
ibi = "8JMKD3MGP3W34R/44LJNEL",
url = "http://urlib.net/ibi/8JMKD3MGP3W34R/44LJNEL",
targetfile = "publicacao.pdf",
urlaccessdate = "10 maio 2024"
}