Upper atmospheric electrical discharges

Our understanding of upper atmospheric discharges has advanced significantly since the early 1990s, and a large amount of dedicated observational, experimental, theoretical, and modeling efforts have been made to study various aspects of TLEs. Many papers, including a few recent extensive review papers, have been published in this field [Pasko, 2007, 2008; Neubert et al., 2008; Roussel-Dupre et al., 2008; Mishin and Milikh, 2008; Ebert and Sentman, 2008; Siingh et al., 2008; Pasko, 2010; Ebert et al., 2010; Pasko et al., 2011; Stenbaek-Nielsen et al., 2013; Pasko et al., 2013]. A book dedicated to TLEs was also published in 2006[Fυllekrug et al., 2006], and discussions on different aspects of TLEs appear in several other books [Rakov and Uman, 2003; Leblanc et al., 2008; Cooray, 2012] and in journal special issues or sections [Ebert and Sentman, 2008; Sentman, 2010; Gordillo-Vαzquez and Luque, 2013]. In this chapter, we attempt to give an overview of the TLE research and our knowledge of them. The general phenomenology of different types of TLEs is described in section 17.2. Section 17.3 discusses similarity laws for gas discharges at different pressures or gas densities, and presents an example illustrating possible distinctions between the discharges at different pressures. In section 17.4, we present example studies of modeling sprites (arguably the best documented TLEs) and their fine structures in order to show how TLE modeling is carried out and how it helps improve our understanding of TLEs.