FORTE observations of simultaneous VHF and optical emissions from lightning: Basic phenomenology
- Los Alamos National Laboratory, Space and Atmospheric Sciences Group, Los Alamos, New Mexico (United States)
- Sensors and Electronics Department, Sandia National Laboratories, Albuquerque, New Mexico (United States)
Preliminary observations of simultaneous VHF and optical emissions from lightning as seen by the Fast on-Orbit Recording of Transient Events (FORTE) spacecraft are presented. VHF/optical waveform pairs are routinely collected both as individual lightning events and as sequences of events associated with cloud-to-ground (CG) and intracloud (IC) flashes. CG pulses can be distinguished from IC pulses on the basis of the properties of the VHF and optical waveforms but mostly on the basis of the associated VHF spectrograms. The VHF spectrograms are very similar to previous ground-based HF and VHF observations of lightning and show signatures associated with return strokes, stepped and dart leaders, attachment processes, and intracloud activity. For a typical IC flash, the FORTE-detected VHF is generally characterized by impulsive broadband bursts of emission, and the associated optical emissions are often highly structured. For a typical initial return stroke, the FORTE-detected VHF is generated by the stepped leader, the attachment process, and the actual return stroke. For a typical subsequent return stroke, the FORTE-detected VHF is mainly generated by dart leader processes. The detected optical signal in both return stroke cases is primarily produced by the in-cloud portion of the discharge and lags the arrival of the corresponding VHF emissions at the satellite by a mean value of 243 {mu}s. This delay is composed of a transit time delay (mean of 105 {mu}s) as the return stroke current propagates from the attachment point up into the region of in-cloud activity plus an additional delay due to the scattering of light during its traversal through the clouds. The broadening of the light pulse during its propagation through the clouds is measured and used to infer a mean of this scattering delay of about 138 {mu}s (41 km additional path length) for CG light. This value for the mean scattering delay is consistent with the Thomason and Krider [1982] model for light propagation through clouds. (c) 2000 American Geophysical Union.
- OSTI ID:
- 20215812
- Journal Information:
- Journal of Geophysical Research, Vol. 105, Issue D2; Other Information: PBD: 27 Jan 2000; ISSN 0148-0227
- Country of Publication:
- United States
- Language:
- English
Similar Records
Combined Optical and Radio-Frequency Perspectives on a Hybrid Cloud-To-Ground Lightning Flash Observed by the FORTE Satellite
Combined Optical and Radio-Frequency Measurements of a Lightning Megaflash by the FORTE Satellite