C. B. Moore

Electricity in Volcanic Clouds Investigations show that lightning can result from charge-separation processes in a volcanic crater

In November of 1963 an oceanic volcano produced an island, Surtsey, just off the southern coast of Iceland. The volcanic crater was often flooded with sea water. Vigorous eruptions of steam and tephra were accompanied by an enhancement of the normal fine-weather potential gradient, and lightning was often observed. Measurements of atmospheric electricity and visual and photographic observations lead us to believe that the electrical activity is caused by the ejection from the volcano into the atmosphere of material carrying a large positive charge. The concentration of charge in the eruption plume as it issued from the orifice of the volcano is estimated to be of the order of 105 or 106 elementary charges per cubic centimeter.

Gushes of Rain and Hail After Lightning

Abstract Observations of thunderstorms in New Mexico were made with a vertically-scanning, 3-cm radar on a mountain top. Prior to a cloud-to-ground lightning discharge nearby, the radar echo overhead was usually quite weak, indicating low intensities of precipitation there. Following the lightning it was observed sometimes that in the region of the cloud where the discharge occurred the radar echo intensity rapidly increased, and shortly thereafter a gush of rain or hail fell nearby. These studies confirm earlier radar observations, made by the authors at Grand Bahama Island, B.W.I., in which it was found that lightning is often followed in the cloud by a rapidly intensifying echo and then by a gush of rain at the ground. The increases in radar reflectivity in small volumes of the cloud following lightning suggest that the electric discharge is influencing the size of particles in the cloud. An analysis indicates that within 30 seconds after a lightning discharge, the mass of some droplets may increase as...

Electric Potential Gradients above Thunderstorms

Abstract Measurements of the electric potential gradient from a U-2 airplane flying over thunderstorms show that sustained gradients occurred only in the vicinity of convective cloud disturbances that rose above the stratiform anvil cloud. The potential gradient often reversed in polarity immediately after lightning occurred in the cloud. We interpret these effects as indicating the presence of a charged screening layer at the upper cloud boundary. The observations further suggest to us that Wilson conduction currents flow from thunderstorms to the upper atmosphere for only as long as convection continues.

An explanation for anomalous lightning from forest fire clouds

Experiments out of doors and in a wind tunnel show that when trees, vegetation, and other substances are burned in the open air, negative charge is released into the atmosphere under the influence of the fine weather electric field. The results indicate that the thunderclouds formed as the result of a forest fire have probably grown from air that contains negative, instead of the usual positive, fine weather space charge. Observations showing that cumulonimbus clouds formed over forest fires produced positive, instead of the usual negative, cloud-to-ground lightning, suggest that the electrification of these clouds may have been caused by one or more influence mechanisms.

Measurements of the electrical conductivities of air over hot water

Abstract Measurements of the conduction current between two electrodes in air over recently boiled water have been interpreted by Carlon as indicating that the humidified air became highly conductive and that large numbers of ions were produced in the air after it was saturated with water vapor. These interpretations have been questioned because it is possible that the insulators used in the high-humidity experiments allowed leakage currents to flow and these were treated as though they were conduction currents through the air. We repeated these measurements with the use of a conventional, Gerdien cylinder conductivity-measuring apparatus that had insulators heated to temperatures above the dew point of the water vapor in the air being measured so that the insulators maintained high resistances. The results from the heated Gerdien cylinder experiments contradict the suggestions of high conductivities in humid air, for the measured conductivities of air were repeatedly observed to decrease by about 50% whe...

LeRoy Meisinger, Part II: Analysis of the Scientific Ballooning Accident of 2 June 1924*

During the spring of 1924, U.S. Weather Bureau meteorologist LeRoy Meisinger conducted a series of experiments with a free balloon to determine the trajectories of air around extratropical cyclones. The 10th flight in the series ended with a crash of the balloon over central Illinois. Both Meisinger and the pilot, Army Air Services Lt. James Neely, were killed. An effort has been made to reconstruct this accident using information from a review article by early twentieth-century meteorologist Vincent Jakl and newspaper accounts of the accident. The principal results of the study follow. 1) Meisingers balloon was caught in the downdraft of a newly developed thunderstorm over the Bement, Illinois, area on the evening of 2 June; 2) a hard landing took place in a cornfield just north of Bement, and loss of ballast at the hardlanding site was sufficient to cause the balloon to rise again; and 3) after rebounding from the ground, the balloon with the two aeronauts aboard was struck by lightning. A fire resulted that burned through the netting and led to a crash four miles northeast of the hard-landing site

APPARATUS USING RADIOACTIVE PROBES FOR MEASURING THE VERTICAL COMPONENT OF ATMOSPHERIC POTENTIAL GRADIENT FROM AN AIRPLANE

An apparatus for measuring and recording the atmospheric potential gradient from an aircraft is described. lt consists of two radioactive probes connected through an electromechanical coupling device to a conventional electrometer and recorder. (auth)