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@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/rep/8JMKD3MGP3W34P/3LG4CDL",
           targetfile = "publicacao.pdf",
        urlaccessdate = "28 nov. 2020"
}


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