HR: 08:50h
AN: AE51A-04 INVITED     [PDF]
TI: Role of Neutral Density and Conductivity Perturbations in Determining Sprite Initiation Locations
AU: * S\~{a}o Sabbas, F T
EM: fsaosabbas@dae.inpe.br
AF: Instituto Nacional de Pesquisas Espaciais - INPE, Aeronomy Division - DAE/INPE Av. dos Astronautas 1758 Jd. Granja, Sao Jos‚ dos Campos, SP 12227-010 Brazil
AU: Sentman, D D
EM: dsentman@gi.alaska.edu
AF: University of Alaska Fairbanks - UAF, Geophysical Institute, UAF, Fairbanks, AK 99775-7320 United States
AU: Otto, A
EM: ao@how.gi.alaska.edu
AF: University of Alaska Fairbanks - UAF, Geophysical Institute, UAF, Fairbanks, AK 99775-7320 United States
AB: Multiple sprites are often observed to occur simultaneously, laterally displaced from the underlying causative cloud-to-ground (CG) lightning discharge. The causes of this lateral displacement are presently not understood. This paper investigates the role of neutral density perturbations in determining the locations of sprite initiation. The work was motivated by two previous studies: (1) A detailed statistical showing that the distribution of sprite offsets relative to the underlying lightning had a mean of ~40 km [S\~{a}o Sabbas et al., 2003]. (2) A follow-up study for the same observations showing that the maximum sprite and -CG production of the system were simultaneously reached at the time of maximum contiguous cloud cover of the coldest region, corresponding to the period of greatest convective activity of the system [S\~{a}o Sabbas and Sentman, 2003]. Thunderstorm convective activity is a potential source of gravity waves and mesospheric turbulence, which create an inhomogeneous neutral density background. For this paper computer simulations of the temporal-spatial evolution of lightning-induced electric fields in an inhomogeneous mesospheric neutral density and conductivity were performed. The results indicate that electrical breakdown is facilitated in isolated regions of density depletions at sprite initiation altitudes. These spatially distributed breakdown regions provide the seed electrons necessary for sprite generation, and may account for the observed sprite offsets. Furthermore, neutral density depletions may play a critical role in setting the overall sprite activity level above a thunderstorm.
DE: 0310 Airglow and aurora
DE: 2427 Ionosphere/atmosphere interactions (0335)
DE: 2435 Ionospheric disturbances
DE: 3304 Atmospheric electricity
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2003 Fall Meeting