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H. H. Jonsson
and
B. Vonnegut

Abstract

Apparatus has been designed and constructed for real-time measurements of the electrical conductivity of rainwater. It utilizes a spinning disk that centrifuges and collects the rainwater failing on it A micro conductivity cell is employed, which consists only of electrodes, and needs no embodiment to sustain the rain sample during measurement. Instead the liquid is retained between the electrodes by its own surface tension. Only the order of a microliter of rain water is needed to obtain a inclement. The system's response time is about a second. Test runs during thunderstorms and frontal rains reveal that variations in conductivity by up to a factor of 5 occur during a storm event. Maximum conductivities of up to 160 μS cm−1 usually occurred at the beginning of the storms. In one thunderstorm rainwater conductivity as low as 5 μS cm−1 was measured for a duration of a few minutes.

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A. K. Kamra
and
B. Vonnegut

Abstract

A laboratory experiment has been performed to study the relative effect of aerodynamic and electrical forces an small electrically conducting particles of radii 100–200 μ colliding with a particle of 2 mm radius suspended in an upward moving vertical air stream of a wind tunnel and placed in a vertical polarizing electric field. It has been observed, in a low electric field, that the smaller particles collide and move up with the air stream. However, as the electric field is increased, the smaller particles start coming down, after the collision, against the air stream. The electric field required for this change of direction for different particle sizes is higher for the larger angles of collision. When these results are applied to thunderstorms with high electric fields, it is shown that the electrical forces on the charged cloud particles must be taken into account in any consideration of the gravitational separation of charges. Our experimental results indicate that in high electric fields these electric forces can limit and even oppose the further separation of charges.

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Bernard Vonnegut
and
Charles B. Moore

Apparatus is described for measuring and recording the atmospheric potential gradient from an aircraft. It consists of two radioactive probes connected through an electromechanical coupling device to a conventional electrometer and recorder.

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J. J. Jones
,
C. Grotbeck
, and
B. Vonnegut

Abstract

A simple instrument that detects ice particles has been developed for use in airplane studies of thunderstorms. Although sophisticated instruments are available for imaging atmospheric ice particles, the spatial resolution of the particle concentration determined from their data is limited by the small size of the sample area. The ice detector described here provides a real-time indication of the presence of ice crystals within and in the vicinity of clouds, and provides an approximate measure of their concentrations with excellent spatial resolution. This device, which is simple and inexpensive, has been flown for five summers in New Mexico thunderstorms.

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J. D. McTaggart-Cowan
,
G. G. Lala
, and
B. Vonnegut

Abstract

An aircraft instrument is described that gives a real-time measurement of the number of ice crystal particles per unit volume in cirriform clouds. Its method of detection is based on the mechanisms of contact electrification, as applied to the collision between a stainless steel wire and an ice crystal. The signal conditioner, which employs a series of integrated circuits, converts the frequency of crystal collisions into a voltage. Several examples of actual flights are shown.

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C. B. Moore
,
B. Vonnegut
,
E. A. Vrablik
, and
D. A. McCaig

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 much as 100-fold as the result of an electrostatic precipitation effect.

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B. Vonnegut
,
C. B. Moore
,
R. P. Espinola
, and
H. H. Blau Jr.

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.

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