HR: 13:40h
AN: AE13A-01 INVITED     [Abstracts]
TI: Terrestrial Gamma-ray Flashes and Lightning Discharges
AU: * Inan, U S
EM: inan@stanford.edu
AF: STAR Lab, Electrical Engineering, 350 Serra Mall, Stanford, CA 94305 United States
AU: Cohen, M
EM:
AF: STAR Lab, Electrical Engineering, 350 Serra Mall, Stanford, CA 94305 United States
AU: Lehtinen, N G
EM:
AF: STAR Lab, Electrical Engineering, 350 Serra Mall, Stanford, CA 94305 United States
AU: Said, R
EM:
AF: STAR Lab, Electrical Engineering, 350 Serra Mall, Stanford, CA 94305 United States
AU: Smith, D M
EM:
AF: Physics Department and Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 United States
AU: Lopez, L I
EM:
AF: Astronomy Department and Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
AB: The observation of brief (<1 ms) bursts of intense γ-rays, the so-called Terrestrial Gamma-ray Flashes (TGFs), by the BATSE γ-ray experiment was one of the most unexpected discoveries by the Compton Gamma-Ray Observatory. Extensive modeling efforts following this observation interpreted the observations in the context of the runaway acceleration of energetic (>1 MeV) electrons by the intense quasi-static fields that temporarily exist at high altitudes above thunderclouds following positive cloud-to-ground lightning discharges. Association of individual TGFs, and positive cloud to ground (CG) lightning strikes have been demonstrated by means of the measurement of associated radio atmospherics, with at least some of the correlated sferics showing properties similar to those that cause sprites. However, simultaneous VLF data was only available for a few of the BATSE/CGRO events, so that a comprehensive study of this association was not feasible. New evidence from the RHESSI spacecraft now shows that TGFs occur much more commonly and that the photon energies typically extend to ~20 MeV. With the much larger number of TGFs now available from RHESSI, we undertake here a comprehensive study of the association between TGFs and sferics using VLF data collected at Palmer Station, Antarctica and other sites (e.g., in Alaska and the continental United States). Results indicate that by far the majority of observed TGFs are associated with an ELF/VLF radio atmospheric observed at Palmer Station, within ±1.5 ms of the expected time (when the sferic and the TGF propagation times are accounted for) and directionally determined to be arriving from an azimuth that is within <2.5° of the RHESSI footprint. Compared with other sferics arriving from the same azimuth during a 30-min period around the time of the events, the sferics associated with the RHESSI TGF tend to be those with relatively large peak VLF intensities. This observation has led to the introduction of a new model [Inan & Lehtinen, 2005] for the production of TGFs by the electromagnetic impulses (EMPs) radiated by lightning discharges, which is also briefly discussed. Although only a few RHESSI TGF events are found for which there are no radio atmospherics arriving from the direction of RHESSI, these events are also analyzed and presented in detail, as they may represent the more interesting cases I which the source lightning may be in the conjugate hemisphere, may involve unusual type of lightning discharges that do not efficiently excite radio atmospherics, or may imply be produced in the absence of lightning discharges.
DE: 2423 Ionization processes (7823)
DE: 2427 Ionosphere/atmosphere interactions (0335)
DE: 2435 Ionospheric disturbances
DE: 2451 Particle acceleration
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: Fall Meeting 2005