@PhDThesis{Campos:2016:MeLeMu,
author = "Campos, Leandro Zanella de Souza",
title = "On the mechanisms that lead to multiple ground contacts in
lightning",
school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
year = "2016",
address = "S{\~a}o Jos{\'e} dos Campos",
month = "2016-05-11",
keywords = "lightning, cloud-to-ground discharges, cluster analysis, ground
contact points, multiple ground terminations, rel{\^a}mpagos,
descargas nuvem-solo, an{\'a}lise de agrupamento, pontos de
contato, m{\'u}ltiplas termina{\c{c}}{\~o}es no solo.",
abstract = "Negative cloud-to-ground (-CG) lightning is an essentially
discrete phenomenon (with multiple individual return strokes) and
frequently strikes ground on more than one location. The main
objective of this thesis work is to bring new light into the
mechanisms through which a CG can produce more than one ground
termination and which factors modulate that characteristic. The
first step towards that goal was the development of an algorithm,
named groupGCP, that is capable of processing data provided by
VLF/LF Lightning Location Systems (LLS) and deriving ground
contact point (GCP) information by grouping each stroke into an
optimized strike point position. This is the first method of this
kind that makes full use of all error ellipse parameters provided
by some of the present day sensor technologies. The second step
concerns detailed individual case studies of lightning events. The
first of these analyses approaches the phenomenology of forked and
upward-illumination strokes. They are capable of touching ground
at multiple locations within very short intervals, ranging from a
few microseconds up to a few milliseconds. Some crucial
differences between these two classes of events are identified and
discussed in detail. Next, the more common subsequent new ground
contact (NGC) stroke is analyzed from data provided by a
three-dimensional VHF Lightning Mapping Array (LMA) along with
auxiliary information provided by VLF/LF LLS, video and electric
field records. Three very distinct mechanisms that lead to NGC
subsequent strokes were identified: Type I consists of dart
leaders that diverge from the path of the preceding stroke; Type
II originate from in-cloud horizontally propagating channels that
move away from the preceding GCP during the interstroke interval;
and Type III consists of NGC subsequent strokes that originate as
apparently independent stepped leader processes. The sample of
events of each class suggests that Type I commonly produce ground
terminations up to 1 km away from the preceding GCP, while Types
II and III may lead to horizontal separations between GCPs of more
than 7 km. In the third step some factors that may modulate the
occurrence and characteristics of multi-grounded flashes are
analyzed. Spatial distributions are compared with complex terrain
features (both absolute altitude and high spatial frequency
variations) for three different domains. No consistent correlation
was found for all of them and, although some insights could be
obtained, further investigations with additional instruments are
necessary to evaluate any possible relationship. Also, diurnal
climatology of the mean number of channels per flash and the
separation between them were obtained. All three domains presented
very similar diurnal cycles, suggesting that there may be driving
factors or mechanisms that are shared among all of them. However,
the possibility that the observed trends are actually caused by
classification errors by the algorithm is also discussed. Finally,
the thesis concludes with two examples of technological
applications of the groupGCP algorithm: the improvement of risk
assessment techniques that are suggested by international
lightning protection standards, and the analysis of
lightning-caused power line faults. RESUMO: Rel{\^a}mpagos
nuvem-solo negativos s{\~a}o fen{\^o}menos essencialmente
discretos (apresentando m{\'u}ltiplas descargas de retorno
individuais) e frequentemente atingem o solo em mais de um local.
O objetivo principal desta tese {\'e} obter novas
informa{\c{c}}{\~o}es acerca dos mecanismos atrav{\'e}s dos
quais um rel{\^a}mpago pode produzir mais de um ponto de contato.
O primeiro passo nesta dire{\c{c}}{\~a}o consiste no
desenvolvimento de um algoritmo denominado groupGCP, capaz de
processar dados de redes de detec{\c{c}}{\~a}o de larga escala
(em VLF/LF) e obter informa{\c{c}}{\~o}es de pontos de contato
ao agrupar descargas de retorno individuais. Este {\'e} o
primeiro m{\'e}todo desta natureza que utiliza integralmente as
informa{\c{c}}{\~o}es de elipses de erro fornecidas por alguns
tipos de sensores atuais. O segundo passo envolve estudos de caso
detalhados de rel{\^a}mpagos individuais. A primeira destas
an{\'a}lises aborda a fenomenologia de rel{\^a}mpagos bifurcados
e do tipo \${{"}}\$upward illumination\${{"}}\$. Esta classe
de fen{\^o}menos {\'e} capaz de tocar o solo em m{\'u}ltiplos
locais dentro de per{\'{\i}}odos de tempo muito curtos, de
alguns microssegundos at{\'e} alguns milissegundos. Algumas
diferen{\c{c}}as cruciais entre os dois tipos foram identificadas
e discutidas em detalhes. Em seguida, casos de
forma{\c{c}}{\~a}o de novos pontos de contato em descargas de
retorno subsequentes s{\~a}o analisados atrav{\'e}s de dados de
mapeamento em tr{\^e}s dimens{\~o}es fornecidos por uma rede LMA
(Lightning Mapping Array) juntamente com dados auxiliares de redes
de detec{\c{c}}{\~a}o em VLF/LF, v{\'{\i}}deo e campo
el{\'e}trico. Tr{\^e}s mecanismos distintos de
inicia{\c{c}}{\~a}o de novos pontos de contato foram
identificados: Tipo I consiste em l{\'{\i}}deres
cont{\'{\i}}nuos que divergem do canal de uma descarga anterior;
Tipo II origina-se em canais que se propagam horizontalmente no
interior da nuvem de tempestade; e Tipo III consiste em descargas
de retorno subsequentes que se formam em l{\'{\i}}deres
escalonados independentes. A amostra de eventos de cada classe
sugere que Tipo I normalmente produz pontos de contato a at{\'e}
1 km do ponto anterior, enquanto Tipos II e III podem levar a
separa{\c{c}}{\~o}es entre contatos de at{\'e} mais de 7 km. No
terceiro passo alguns fatores que podem modular a ocorr{\^e}ncia
e caracter{\'{\i}}sticas de rel{\^a}mpagos com m{\'u}ltiplos
pontos de contato s{\~a}o analisados. Distribui{\c{c}}{\~o}es
espaciais foram comparadas com dados de relevo (tanto em altitude
absoluta quanto em varia{\c{c}}{\~o}es espaciais de alta
frequ{\^e}ncia) em tr{\^e}s dom{\'{\i}}nios diferentes.
Nenhuma correla{\c{c}}{\~a}o consistente entre os tr{\^e}s
dom{\'{\i}}nios p{\^o}de ser encontrada, e ainda que algumas
informa{\c{c}}{\~o}es novas tenham sido obtidas, estudos futuros
com instrumentos adicionais s{\~a}o necess{\'a}rias.
Climatologias diurnas foram geradas para o n{\'u}mero m{\'e}dio
de canais por raio e a separa{\c{c}}{\~a}o entre eles. Os
tr{\^e}s dom{\'{\i}}nios apresentaram ciclos diurnos bastante
semelhantes, o que sugere que podem existir fatores ou mecanismos
comuns a todos eles. Por outro lado, tamb{\'e}m se discute a
possibilidade de que as tend{\^e}ncias observadas foram na
verdade causadas por erros de classifica{\c{c}}{\~a}o do
algoritmo. Finalmente, a tese {\'e} conclu{\'{\i}}da com dois
exemplos de aplica{\c{c}}{\~o}es tecnol{\'o}gicas envolvendo o
uso do algoritmo groupGCP: o aprimoramento de t{\'e}cnicas de
avalia{\c{c}}{\~a}o de risco que s{\~a}o sugeridas por
padr{\~o}es internacionais de prote{\c{c}}{\~a}o contra
descargas atmosf{\'e}ricas, e a an{\'a}lise de falhas em linhas
de distribui{\c{c}}{\~a}o que s{\~a}o causadas por
rel{\^a}mpagos.",
committee = "Lago, Alisson Dal (presidente) and Pinto Junior, Osmar
(orientador) and Cummins, Kenneth L. (orientador) and Gobbi,
Delano and Saba, Marcelo Magalh{\~a}es Fares and Bourscheidt,
Vandoir and Saraiva, Antonio Carlos Varela",
copyholder = "SID/SCD",
englishtitle = "Sobre os mecanismos que levam {\`a} produ{\c{c}}{\~a}o de
m{\'u}ltiplos pontos de contato em rel{\^a}mpagos",
language = "en",
pages = "280",
ibi = "8JMKD3MGP3W34P/3LG4CDL",
url = "http://urlib.net/ibi/8JMKD3MGP3W34P/3LG4CDL",
targetfile = "publicacao.pdf",
urlaccessdate = "27 abr. 2024"
}