HR: 12:05h
AN: AE52A-07    [Abstracts]
TI: Simulation of Spectral Characteristics of Sprites From Runaway and Conventional Breakdown Processes and Comparison to Measurements
AU: * Triplett, L A
EM: ltriplett@lanl.gov
AF: Los Alamos National Laboratory, EES-2, MS F665, Los Alamos, NM 87545 United States
AU: Roussel-Dupre, R A
EM: rroussel-dupre@lanl.gov
AF: Los Alamos National Laboratory, EES-2, MS F665, Los Alamos, NM 87545 United States
AU: Colman, J J
EM: jonah@lanl.gov
AF: Los Alamos National Laboratory, EES-2, MS D401, Los Alamos, NM 87545 United States
AU: Symbalisty, E M
EM: emds@aftac.gov
AF: AFTAC/TTAD, 1030 S. Highway A1A, Patrick AFB, FL 32925-3002 United States
AB: The breakdown processes that lead to sprite formation are still being debated. Are sprites formed through conventional breakdown, runaway breakdown, or a combination of both? What are the thunderstorm electrical conditions that produce one or the other or both processes? This study describes the improved two-dimensional fully electromagnetic Unified Maxwell (UNIMAX) model and an updated methodology to derive the associated optical spectra using the Physics-based Optical Emission Model (POEM). These models allow us to study the differences between conventional and runaway breakdown processes and obtain a better understanding of what information can be garnered from sprite spectral measurements. A detailed kinetic computational tool, Plume, has been developed to compute the self-consistent evolution of a seed electron population with energies from 0 to 50 MeV in the presence of a steady-state, spatially-uniform electric field (see Colman et al. abstract submitted to this meeting). This information is used to compute steady-state emission rates as a function of the applied electric field for 13 Nitrogen and 3 Oxygen band systems. These rates can be combined with the number and energy of electrons from the UNIMAX sprite model and quantum transition information from POEM to separate the band system into individual lines and generate simulated spectral images. Cascading between different bands is also included. Spectral measurements of sprites represent a temporal and spatial superposition of emissions. These emissions emanate from a wide variety of electrical and gas discharge conditions that exist along the body of the sprite and which change as a function of time. Interpretation of the spectra to obtain the properties of the gas is made difficult by this inherent averaging process and the fundamental discharge mechanism can be obscured. Thus, we fold in the properties of spectrometers (i.e. spatial and temporal averaging, slit size, atmospheric absorption, etc.) to compare with measurements and assess the effect of temporal and spatial averaging. These spectra can then be used to elucidate what would be theoretically observed separately from runaway and conventional breakdown and to suggest potential measurements that could differentiate between the different processes.
DE: 3324 Lightning
DE: 3304 Atmospheric electricity
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting