E. P. Krider

A Search for X Rays from Helium and Air Discharges at Atmospheric Pressure

X‐ray production in wide‐gap helium and air discharges was investigated using calibrated film‐badge detectors. Helium discharges were found to produce x rays with average energies in the range <11 to 13 keV. The energies were independent of applied electric field for average E/p ratios between 35 and 140 V/cm·Torr. X‐ray intensities were proportional to the atomic number of the electrode material. No evidence for similar x‐ray production was found in air discharges.

Submicrosecond field variations during the onset of first return strokes in cloud‐to‐ground lightning

An experiment to measure the electric field E and dE/dt signatures that are radiated by the first return stroke in cloud-to-ground lightning was conducted on the eastern tip of Cape Canaveral, Florida, during the summer of 1984. At this site, there was minimal distortion in the fields due to ground wave propagation when the lightning struck within a few tens of kilometers to the east over the Atlantic Ocean. Biases that are introduced by a finite threshold in the triggered recording system were kept to a minimum by triggering this system on the output of a wideband RF receiver tuned to 5 MHz. Values of the peak dE/dt during the initial onset of 63 first strokes were found to be normally distributed with a mean and standard deviation of 39 ± 11 V m−1 μs−1 after they were normalized to a range of 100 km using an inverse distance relation. Values of the full width at half maximum (FWHM) of the initial half-cycle of dE/dt in 61 first strokes had a mean and standard deviation of 100 ± 20 ns and were approximately Gaussian. When these results are interpreted using the simple transmission line model, after correcting for the effects of propagation over 35 km of seawater, the average value of the maximum current derivative, (dI/dt)p, and its standard deviation are inferred to be 115 ± 32 kA μs−1, with a systematic uncertainty of about 30%. The FWHM after correction for propagation is about 75 ± 15 ns. The inferred values of (dI/dt)p are significantly higher than most previous measurements of natural first strokes during direct strikes to instrumented towers but are in good agreement with direct measurements of dI/dt during subsequent return strokes in rocket-triggered discharges in Florida.

Lightning in the Region of the TOGA COARE

Abstract In the fall of 1992 a lightning direction finder network was deployed in the western Pacific Ocean in the area of Papua New Guinea. Direction finders were installed on Kapingamarangi Atoll and near the towns of Rabaul and Kavieng, Papua New Guinea. The instruments were modified to detect cloud-to-ground lightning out to a distance of 900 km. Data were collected from cloud-to-ground lightning flashes for the period 26 November 1992–15 January 1994. The analyses are presented for the period 1 January 1993–31 December 1993. In addition, a waveform recorder was located at Kavieng to record both cloud-to-ground lightning and intracloud lightning in order to provide an estimate of the complete lightning activity. The data from these instruments are to be analyzed in conjunction with the data from ship and airborne radars, in-cloud microphysics, and electrical measurements from both the ER-2 and DC-8. The waveform instrumentation operated from approximately mid-January through February 1993. Over 150 00...

Four‐Meter Sparks in Air

Sparks of 4‐m length in atmospheric air were studied, using high‐speed image‐converter photography, current and voltage measurements, absolute measurements of radiated light intensity, and high‐speed image‐converter spectroscopy. Correlated results of the various measurements are presented. The energy balance of the spark is discussed.

Measurements of radio frequency signals from lightning in Jupiter's atmosphere

During the descent of the Galileo probe through Jupiters atmosphere, the lightning and radio emissions detector (LRD) instrument measured radio frequency signals presumably from electrical discharges in the planets atmosphere. The LRD was the only instrument that provided remote sensing, as well as in situ, measurements of atmospheric characteristics. The LRD measurements are presented here and some estimates are given on the energetics and frequency of occurrence of lightning in Jovian clouds. Propagation calculations of RF discharges in the Jovian atmosphere system and the statistics data obtained by the LRD, together with one very distinct lightning waveform, permit a unified and consistent interpretation of the data. We conclude that at the time of probe entry, Jovian discharges occur with a rate about one hundredth that of the global yearly average on Earth (Earth value is about 6 flashes km−2 yr−1) within about 15,000 km radius of the probe and that the average radiated power is of the order of 5 × 1011 W. The change in the electric dipole moment in Jovian lightning is about 107 coulomb in, roughly 100 times that of a typical terrestrial discharge.

Radio Frequency Signals in Jupiter's Atmosphere

During the Galileo probes descent through Jupiters atmosphere, under the ionosphere, the lightning and radio emission detector measured radio frequency signals at levels significantly above the probes electromagnetic noise. The signal strengths at 3 and 15 kilohertz were relatively large at the beginning of the descent, decreased with depth to a pressure level of about 5 bars, and then increased slowly until the end of the mission. The 15-kilohertz signals show arrival direction anisotropies. Measurements of radio frequency wave forms show that the probe passed through an atmospheric region that did not support lightning within at least 100 kilometers and more likely a few thousand kilometers of the descent trajectory. The apparent opacity of the jovian atmosphere increases sharply at pressures greater than about 4 bars.

Lightning and the Apollo 17/Saturn V Exhaust Plume

Survey spectra of the Apollo 17/Saturn V exhaust plume during launch were obtained in the ultraviolet, visible, and near infrared. The plume resembles a blackbody source for about 40 m from the exit plane, and beyond this point the characteristic radiation is the sodium D-lines. The spectral data support previous reports mat the peak exhaust temperature is near 2600 K, which in turn suggests the conductivity in the upper 40 m of plume is in the range 10 7 to 10 4 mho/cm or higher. We examine the implication of these results for the initiation of lightning such as occurred during the launch of Apollo 12.