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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Positive cloud-to-ground lightning flashes in severe storms

The occurrence of cloud-to-ground flashes that effectively lower positive charge to earth (+CG flash) over flat terrain has been documented in the mature stage of severe thunderstorms. Of the 31 documented +CG flashes, most had only one return stroke. Zero-to-peak rise times for the strokes averaged 7 microsec. The +CG flashes averaged 520 ms in duration, with 25 percent lasting more than 800 ms. Many of these had field changes suggestive of continuing current. Positive flashes have been observed to emanate from several regions of severe storms: high on the back of the main storm tower, through the wall cloud, and from the downshear anvil. Visually most of these positive flashes have emanated from high in the storm, and acoustic mapping of two shows thunder sources to a height of about 15 km.

Rust, W. D.↗
NASA NTRS1983

Aircraft lightning-induced voltage test technique developments

High voltage safety, fuels safety, simulation, and response/measurement techniques are discussed. Travelling wave transit times, return circuit conductor configurations, LC ladder network generators, and repetitive pulse techniques are also discussed. Differential conductive coaxial cable, analog fiber optic link, repetitive pulse sampled data instrumentation system, flash A/D optic link system, and an FM telemetry system are considered.

Crouch, K. E.↗
NASA NTRS1983

Acoustic and electric signals from lightning

Observations of infrasound apparently generated by the collapse of the electrostatic field in the thundercloud, are presented along with electric field measurements and high-frequency thunder signals. The frequency of the infrasound pulse is about 1 Hz and amplitude a few microbars. The observations seem to confirm some of the theoretical predictions of Wilson (1920) and Dessler (1973). The signal is predominated by a compressional phase and seems to be beamed vertically. Calculation of the parameters of the charged region using the infrasound signal give reasonable values.

Balachandran, N. K.↗
NASA NTRS1984

Formation of Meteoritic chonrules by lightning

Chondrules which are enigmatic millimeter sized silicate grains embedded in the most common class of meteorites, the chondritic (stony) meteorites. It is shown that the chondritic rocks formed by sedimentation processes in the solar nebula, and that it escaped the subsequent melting processes which differentiated the planets from the meteorite parent bodies.

Wasson, J. T.↗
NASA NTRS1985

The production of lightning-associated infrasonic acoustic sources in thunderclouds

Electrostatic production of low frequency (about 1 Hz) acoustic pulses associated with electrical discharges in thunderclouds has been theoretically described (e.g., Wilson, 1920; Dessler, 1973) and experimentally observed (e.g., Bohannon et al., 1977; Balachandran, 1983). The measured waveforms differ consistently with the theories in that the observed wave has an initial positive (or condensation) pulse followed by a negative (or rarefaction) pulse; whereas theories predicted only a negative pulse. The electrical heating of the air by positive streamer systems during the discharge is computed in this theoretical paper. This rapid (supersonic) electrical heating, although small (about 10 to the -6th T sub zero), produces a positive pressure perturbation (of about 10 to the -1st Pa), which when added to the negative electrostatic pressure perturbation generates an acoustic wave consistent with measured signals. A positive pulse always precedes the negative pulse in this model, and the positive pulse is always smaller in amplitude than the negative. The durations of the positive and negative pulses are similar. When more realistic models are employed, the observed signal can be related through theory to physical parameters in the thundercloud.

Few, A. A.↗
NASA NTRS1986

The production of trace gases by photochemistry and lightning in the early atmosphere

Recent atmospheric calculation suggest that the prebiological atmosphere was most probably composed of nitrogen, carbon dioxide, and water vapor, resulting from volatile outgassing, as opposed to the older view of a strongly reducing early atmosphere composed of methane, ammonia, and hydrogen. Photochemical calculations indicate that methane would have been readily destroyed via reaction with the hydroxyl radical produced from water vapor and that ammonia would have been readily lost via photolysis and rainout. The rapid loss of methane and ammonia, coupled with the absence of a significant source of these gases, suggest that atmospheric methane and ammonia were very short lived, if they were present at all. An early atmosphere of N2, CO2, and H2O is stable and leads to the chemical production of a number of atmospheric species of biological significance, including oxygen, ozone, carbon monoxide, formaldehyde, and hydrogen cyanide. Using a photochemical model of the early atmosphere, the chemical productionof these species over a wide range of atmospheric parameters were investigated. These calculations indicate that early atmospheric levels of O3 were significantly below the levels needed to provide UV shielding. The fate of volcanically emitted sulfur species, e.g., sulfur dioxide and hydrogen sulfide, was investigated in the early atmosphere to assess their UV shielding properties. The photochemical calculations show that these species were of insufficient levels, due in part to their short photochemical lifetimes, to provide UV shielding.

Levine, J. S.↗
NASA NTRS1985

Validation of mesocale number sea breeze thunderstorm forecasts over Florida using LPATS - The Lightning Position and Tracking System

The research reported in the present paper has the objective to develop improved operational techniques for sea breeze (SB) initiated convective storms. It is pointed out that the sea breeze is a relatively simple mesoscale circulation. The considered studies are mainly concerned with detailed thunderstorm potential forecasts during the next several hours, taking into account real-time predictions using new supercomputer technology. Thunderstorm and coastal mesoscale circulations are discussed along with the P3DM model sea. The considered code represents the result of a further development of the NOAA Florida sea breeze model which was introduced by Pielke (1974). After its modificataion, the model was renamed the Prognostic Three Dimensional Mesoscale (P3DM) Model, with its 2-D connterpart the P2DM. Attention is also given to real time climatology, and a case study concerned with developments occurring on 5 May 1984 over the Florida Peninsula.

Lyons, W. A.↗
NASA NTRS1986

The amplitude spectra of lightning radiation fields in the interval from 1 to 20 MHz

Amplitude spectra of the fast-rising initial portion of the EM fields produced by return strokes, leader steps, and cloud pulse are presented. These data have been derived from ground-based measurements of dE/dt signatures that were recorded in the time domain on a triggered oscilloscope. The spectral amplitudes of first return strokes match previously published data at 1 MHz and decrease with increasing frequency, as 1/f between 1 and about 6 MHz and as 1/f squared between 6 and 20 MHz. The spectral amplitudes of leader steps just before return strokes and the fast portion of cloud pulses that triggered the recording system tend to lie 5 to 10 dB below the amplitudes of first return strokes over the entire frequency interval.

Weidman, C. D.↗
NASA NTRS1988

Telemetry interference incorrectly interpreted as evidence for lightning and present-day volcanism at Venus

Spike-like responses to interruptions in the data recorded by the Pioneer Venus Orbiter electric field detector, identified as broadband whistler noise by Singh and Russell (1986), are analyzed. It is shown that these spikes are nonphysical artifacts of the processing of interruptions in telemetry data, and that they are readily distinguishable from other nonartificial noise apppearing in the measurements. It is suggested that key portions of the results of Singh and Russell are compromised by the inclusion of the artificial data. It is concluded that the present electric field data set provides no evidence for inferring the presence of either lighning or present-day volcanism at Venus.

Taylor, Harry A., Jr.↗