Engineering topics

Few, A. A.

Publications and source records attributed to Few, A. A..

8 records

NASA NTRS1993

Ground-based instrumentation for measurements of atmospheric conduction current and electric field at the South Pole

Attention is given to instruments constructed to measure the atmospheric conduction current and the atmospheric electric field - two fundamental parameters of the global-electric circuit. The instruments were deployed at the Amundsen-Scott South Pole Station in January 1991 and are designed to operate continuously for up to one year without operator intervention. The atmospheric current flows into one hemisphere, through the electronics where it is measured, and out the other hemisphere. The electric field is measured by a field mill of the rotating dipole type. Sample data from the first days of operation at the South Pole indicate variations in the global circuit over time scales from minutes to hours to days.

Byrne, G. J.↗

NASA NTRS1989

Electric field measurements within a severe thunderstorm anvil

This paper presents the results of electric field measurements made within a severe thunderstorm in central Oklahoma on June 13, 1983. The observations show the electrical structure of a severe storm anvil to be more complex than the simple structure of a positive interior and thin, negative screening layers. Evidence is found of extensive regions of both positive and negative charge in the interior of the anvil, and the thicknesses of screening layers are found to be about an order of magnitude greater than calculated in previous models. A conceptual model for the development of the electrical structure of thunderstorm anvils is proposed in which anvil dynamics plays an important role.

Byrne, G. J.↗

NASA NTRS1987

In situ measurements and radar observations of a severe storm - Electricity, kinematics, and precipitation

Electric field measurements made inside a multicell severe storm in Oklahoma in 1983 with a balloon-borne instrument are presented. The properties of the electric charge regions, such as altitude, thickness, and charge concentrations, are studied. These measurements are analzyed with meteorological measurements of temperature and humidity, and balloon tracking and radar observations. The relation between the electric charge structure and the precipitation and kinematic features of the storm is examined. The data reveal that the cell exhibits a bipolar charge structure with negative charge below positive charge. The average charge concentrations of the two regions are estimated as -1.2 and 0.15 nC/cu m, respectively; the upper positive charge is about 6 km in vertical extent, and the lower negative charge is less than 1 km in vertical extent.

Byrne, G. J.↗

NASA NTRS1986

Factor of 2 error in balloon-borne atmospheric conduction current measurements

An exact expression is derived for the atmospheric current to a prolate spheroidal antenna. The effective collection area is considered, obtaining a solution for a spherical antenna and the vertical wire antenna. A factor of two error in the studies of the effective area of an antenna of arbitrary geometry by Kasemir and Ruhnke (1958) and Ogawa (1973) is discussed. The effects of the instrument-atmospheric interaction as they apply to the atmospheric conduction current measurement are considered. Electric field enhancement factors for spheroids and approximate solutions for spheroids and other elongated objects are given.

Few, A. A.↗

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 NTRS1983

Some spatial and temporal relationships between lightning and storm structure and evolution

A number of systems were used to study relationships between lightning and other storm parameters. Instrumentation includes a system for locating cloud to ground lightning strike points, an acoustic lightning mapper and very high frequencies (VHF) (30 to 80 MHz) lightning mapper to study the structure and location of lightning, and S band radar to provide other storm data. Several characteristics of the reconstructed lightning have been relatively constant: (1) lightning structure is usually predominately horizontal; (2) lightning tends to occur preferrentially in certain altitude ranges that are only a few kilometers thick and above the O C isotherm; (3) it tends to occur near, but not necessarily inside, cores of high reflectivity (approximately or 45 dBz), and it often connects with regions of relatively weak reflectivity downstream from stronger reflectivity and updraft cores. Other relationships are also discussed.

Macgorman, D. R.↗

NASA NTRS1982

A thundercloud electric field sounding - Charge distribution and lightning

An instrumented free balloon measured electric fields and field changes as it rose through a thundercloud above Langmuir Laboratory, New Mexico. The variation of the electric field with altitude implied that the cloud contained negative space charge of density -0.6 to -4 nC/cu m between 5.5 and 8.0 km MSL. The environmental temperature at these levels ranged from -5 to -20 C. The measurements imply that the areal extent of this negative charge center was significantly greater than that of the cloud's intense precipitation shafts. At altitudes greater than 8 km, the instrument ascended past net positive charge. In addition, positive space charge adjacent to the earth's surface (concentration 0.6 nC/cu m and in the lowest portion of the cloud (1.0 nC/cu m) is inferred from the measurements. Electric field changes from intracloud lightning were interpreted by using a simple model for the developing streamer of the initial phase. Thunder source reconstructions provided estimates for the orientation of lightning channels. Seven 'streamers' so analyzed propagated on the average, at 50,000 m/s and carried a current of 390 A. The mean charge dissipated during a flash was 30 C.

Weber, M. E.↗

NASA NTRS1978

Direct measurements of the atmospheric conduction current

A method of measuring the atmospheric conduction current above the ground has been employed to obtain data for 12 weeks during the first half of 1974. The instrument consists of a split aluminum sphere suspended by insulated wires to a wooden frame. The measuring electronics and the transmitter are enclosed within the spherical structure. The interaction of the instrument with its atmospheric electrical environment is analyzed, and it is shown that in steady state conditions, predictable differences in the instrumentally measured currents and the atmospheric conduction current will be less than 5% and in the nonsteady state situations the difference is less than 20%. Diurnal variations, a probable winter-summer variation, sunrise, and fog effects were observed for the data obtained during fair-weather conditions. Disturbed weather data are interpreted for the effects of low clouds on the atmospheric current. The charge concentrations within overcast clouds sufficient to produce the observed reversed atmospheric currents are estimated to be small in relation to values in thunderclouds.

Burke, H. K.↗