@PhDThesis{Medeiros:2020:ElIoWa,
author = "Medeiros, Claudia",
title = "Electromagnetic ion-cyclotron waves occurrence on the Van Allen
radiation belts using the Van Allen Probes mission dataset",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2020",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2020-03-20",
keywords = "earth's magnetosphere, Van Allen radiation belts, Van Allen Probes
mission, electromagnetic ion-cyclotron waves, neural networks,
magnetosfera terrestre, cintur{\~a}o de radia{\c{c}}{\~a}o Van
Allen, miss{\~a}o Van Allen Probes, ondas eletromagn{\'e}ticas
{\'{\i}}on-ciclotr{\^o}nicas, redes neurais.",
abstract = "Energetic charged particles trapped in Earths magnetic field lines
constitute the so-called Van Allen radiation belts. The inner most
radiation belt is more stable, whereas the outer radiation belt is
more dynamic. Plasma waves can propagate either along or across
geomagnetic field lines and they can interact with charged
particles thereby changing the radiation belt configuration. Among
such waves the electromagnetic ion cyclotron (EMIC) waves, are of
special interest in this work, since they are responsible for
pitch angle-scattering relativistic electrons into the loss cone.
Both pitch angle-resolved electron fluxes data and high
time-resolution magnetic field measurements acquired from the
twin, identically instrumented NASAs Van Allen Probes mission are
used here, and they span a time interval of more than 4 years. The
focus is to investigate the spatial distribution and the
occurrence rate of EMIC waves in the outer Van Allen radiation
belt during this period as well as the possible role played by
EMIC waves in the reconfiguration of an electron butterfly pitch
angle distribution (PAD) shape that resulted in an unusual
electron butterfly PAD shape. A case study (MEDEIROS et al., 2019)
revealed the likely association between EMIC waves occurrence and
such unusual electron butterfly PAD. Then, two machine
learning-based techniques have been employed with the first of
them, referred to as Bag-of-Features (BoF, Medeiros et al.
(2020)), being responsible to find, in a semi-automated way, EMIC
wave events in a 4-year span dataset of magnetic field spectrogram
images, and the second algorithm, known as Self Organizing Map
(SOM, Souza et al. (2016)), would find unusual electron butterfly
PAD shapes.By matching both the EMIC waves and the unusual
electron butterfly PAD shape surveys the following conclusions are
found: (1) the BoF technique performed nearly as good as the
visual classification method with the enormous advantage that the
BoF technique greatly expedites the analysis by accomplishing the
task in just a few minutes; (2) for the period of one full Van
Allen Probes orbit precession the unusual electron butterfly PAD
shape found by Medeiros et al. (2019) is indeed unusual when
considering events wherein there is at least a 10 minutes
persistence. These events correspond to only 0.3% of the whole 1.8
MeV energy electron PADs dataset used for the same interval; (3)
persistent unusual electron butterfly PAD events generally occur
throughout the nightside region, at L-shell locations larger than
about 5RE, with a slightly higher occurrence rate in the
01:0002:00 MLT range; (4) visual inspection of a small subset,
that is, 23 events, containing persistent unusual electron
butterfly PAD shapes show that they are indeed associated with
EMIC waves occurrence for 22 events; (5) it is argued that EMIC
waves can be the dominant factor in the relativistic electron flux
reduction at pitch angles < 45 and > 135 which in turn lead to the
appearance of such unusual electron butterfly PAD shapes. RESUMO:
Ondas de plasma podem se propagar ao longo ou atrav{\'e}s das
linhas de campo geomagn{\'e}tico e podem interagir com
part{\'{\i}}culas carregadas, alterando assim a
configura{\c{c}}{\~a}o do cintur{\~a}o de radia{\c{c}}{\~a}o
Van Allen. Entre essas ondas, existem as ondas
eletromagn{\'e}ticas ion-ciclotr{\^o}nicas (EMIC) que s{\~a}o
de especial interesse neste trabalho, uma vez que s{\~a}o
respons{\'a}veis pelo espalhamento de el{\'e}trons
relativ{\'{\i}}sticos no cone de perda. Para tal s{\~a}o
utilizados dados de fluxos de el{\'e}trons resolvidos por
{\^a}ngulo de inclina{\c{c}}{\~a}o e medi{\c{c}}{\~o}es de
campo magn{\'e}tico de alta resolu{\c{c}}{\~a}o adquiridas da
miss{\~a}o Van Allen Probes da NASA. O foco {\'e} investigar a
distribui{\c{c}}{\~a}o espacial e a taxa de ocorr{\^e}ncia de
ondas EMIC no cintur{\~a}o de radia{\c{c}}{\~a}o Van Allen
externo, bem como o poss{\'{\i}}vel papel desempenhado pelas
ondas EMIC na reconfigura{\c{c}}{\~a}o da
distribui{\c{c}}{\~a}o do {\^a}ngulo de arremesso para um
formato incomum de borboleta. (MEDEIROS et al., 2019) revelou a
prov{\'a}vel associa{\c{c}}{\~a}o entre a ocorr{\^e}ncia de
ondas EMIC e a reconfigura{\c{c}}{\~a}o incomum da
distribui{\c{c}}{\~a}o do {\^a}ngulo de arremesso em formato
borboleta. Duas t{\'e}cnicas baseadas em aprendizado de
m{\'a}quina foram empregadas com a primeira, denominada Bag of
Features (BoF,Medeiros et al. (2020)), para encontrar, de maneira
semi-autom{\'a}tica, os eventos com ondas EMIC em um conjunto de
dados de quatro anos de imagens de espectrograma de campo
magn{\'e}tico, e o segundo algoritmo, conhecido como Mapa Auto
Organiz{\'a}vel (SOM, Souza et al. (2016)), aplicado a uma
por{\c{c}}{\~a}o menor do conjunto de dados para encontrar
formas incomuns de distribui{\c{c}}{\~a}o do {\^a}ngulo de
arremesso. Ao combinar as ondas EMIC e as
distribui{\c{c}}{\~o}es tipo borboleta, obteve-se as seguintes
conclus{\~o}es: (1) a t{\'e}cnica BoF teve desempenho quase
t{\~a}o bom quanto o m{\'e}todo de classifica{\c{c}}{\~a}o
visual, com a enorme vantagem de que a t{\'e}cnica BoF agiliza
muito o an{\'a}lise realizando a tarefa em apenas alguns minutos;
(2) pelo per{\'{\i}}odo de uma precess{\~a}o total da
{\'o}rbita de Van Allen Probes, a forma incomum de PAD de
borboleta encontrada por Medeiros et al. (2019) {\'e} realmente
incomum ao considerar eventos em que h{\'a} pelo menos 10 minutos
de persist{\^e}ncia. Esses eventos correspondem a apenas 0,3 % de
todo o conjunto de dados de PADs de el{\'e}trons com energia de
1,8 MeV para o mesmo intervalo; (3) os eventos PAD incomuns e
persistentes tipo borboleta ocorrem geralmente em toda a
regi{\~a}o noturna, em locais L\−shell maiores que cerca
de 5RE, com uma taxa de ocorr{\^e}ncia um pouco maior no
per{\'{\i}}odo de 01-02 MLT; (4) A inspe{\c{c}}{\~a}o visual
de um pequeno subconjunto, ou seja, 23 eventos, contendo formas
PAD incomuns e persistentes de borboleta mostra que elas
est{\~a}o realmente associadas {\`a} ocorr{\^e}ncia de ondas
EMIC em 22 eventos; (5) argumenta-se que as ondas EMIC podem ser o
fator dominante na redu{\c{c}}{\~a}o do fluxo de el{\'e}trons
relativ{\'{\i}}sticos com {\^a}ngulos de arremesso < 45 e >
135, que por sua vez levam ao aparecimento de tais formas de PAD
de borboleta.",
committee = "Alves, L{\'{\i}}via Ribeiro (presidente) and Vieira, Luis
Eduardo Antunes (orientador) and Silva Souza, Vitor Moura Cardoso
e (orientador) and Sibeck, David Gary (orientador) and Batista,
Inez Staciarini and Santos, Jean Carlo",
englishtitle = "Estudo da ocorr{\^e}ncia e da distribui{\c{c}}{\~a}o espacial
das ondas eletromagn{\'e}ticas {\'{\i}}on-ciclotr{\^o}nicas no
cintur{\~a}o de radia{\c{c}}{\~a}o externo utilizando dados da
miss{\~a}o Van Allen Probes",
language = "en",
pages = "149",
ibi = "8JMKD3MGP3W34R/426C3CB",
url = "http://urlib.net/ibi/8JMKD3MGP3W34R/426C3CB",
targetfile = "publicacao.pdf",
urlaccessdate = "26 abr. 2024"
}