Abstract.With the use of a NaI scintillation detector, bursts of radiation with energies in excess of I MeV were recorded at a mountain-top observatory immediately before three, nearby cloud-to-ground, negative lightning strikes. Coincident recordings of the electric field changes due to the discharges showed that, in each case, the bursts began between I and 2 milliseconds before and continued until the onset of the first return stroke. This radiation was associated with approaching stepped-leaders and may have influenced their development.

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Electric field records have been computer analyzed to determine the lightning statistics for air‐mass thunderstorms at the NASA Kennedy Space Center, Florida. The results for 79 summer storms which produced 10 or more discharges during the years 1976–1980 indicate that cloud and cloud‐to‐ground discharges occur at a mean rate of about 2.4 discharges per minute per storm. The maximum flashing rate over a 5‐min interval was 30.6 discharges per minute on July 14, 1980. Estimates of the monthly area density of all discharges during June, July, and August 1974 through 1980 range from 4 to 27 discharges per km2 per month, with a systematic uncertainty of perhaps a factor of 2 in the sampled area. The mean and standard deviation of the monthly area density over the above years was 12±8 discharges per km2 per month, and the mean area density of just cloud‐to‐ground (CG) flashes is estimated to be 4.6±3.1 CG flashes per km2 per month. Tipping‐bucket rain gauges were operated at each field‐mill site during 1976, 1977, and 1978 as part of the Thunderstorm Research International Program, and the statistics on rainfall are given for 28 storms in 1977 and 1978. Two thunderstorms, one small and one large, were favorably located and relatively stationary, so that the lightning data and surface rainfall could be directly compared. In these storms, there was a good correlation between lightning and rainfall when the latter lagged the former by times of 4 and 9 min. The average rainfall associated with each lightning is estimated to be about 6.7×103 m3 per discharge during the small storm and about 8.5×103 m3 per discharge during the large storm. The average rain volumes associated with each cloud‐to‐ground flash are estimated to be 1.8×104 m3 per CG flash and 2.2×104 m3 per CG flash during these storms, values that are in good agreement with estimates by other investigators.

A series of measurements of electric fields inside active thunderclouds in central New Mexico with instrumented rockets shows that very intense fields (up to 4 X 105 V/m) do exist, although they are rare. In a tabulation of the peak values of the electric field along each trajectory, 4.3 X 104 V/m is the median value. Peak values greater than 105 V/m were encountered only 6 times out of a total of 61 cases. Two examples of very intense fields are presented as case studies. The existence of lightning seems to imply that very intenseelectric fields (perhaps 5 x 105 V/m or more) are sometimes present somewhere inside thunderclouds. However, measurements of field intensities greater than 1 x 105 V/m have been reported only a few times. Kasemir and Holitza [1972] in a conference abstract mentioned seeing a field of 3 x 105 V/m; they have not published a report of the circumstances surrounding this measurement. Gunn [1947] measured from an airplane a momentary field of 1.6 X 105 V/m just before lightning struck the airplane. This measurement is probably incorrect because it was made with a single electric field indicator mounted on the belly of the airplane, which could not have distinguished between cloud electric fields and fields due to charge on the airplane. In a series of measurements of electric fields inside thunderclouds made with instruments suspended from parachutes, Evans [1969] did not detect any fields greater than 3.9 x 104 V/m, but, as Vonnegut [1969] has pointed out, the reliability of his measurements is questionable. During the past 4 years we launched many small rockets instrumented to measure electric fields into active thunderclouds over Langmuir Laboratory in central New Mexico. The purpose of this paper is to analyze what these measurements reveal about the magnitude of electric fields in thunderclouds. We shall first describe how the instrument was modified since our previous description of it. Then we present a statistical description of the data and compile case studies of a few examples of apparently very high fields. THE INSTRUMENT The electric field is measured in the following way: The component of the field perpendicular to the rocket's long axis, E•, causes equal and opposite charges to be induced on two electrodes placed on opposite sides of the instrument housing ( Figure 1). A slight bend in the fins causes the rocket to spin so that the induced charges vary sinusoidally. The charge flow to and from the electrodes passes through an amplifier and is telemetered to ground. Figures 4 and 9 show what the signal coming from the telemetry receiver looks like. The first half of the trace in Figure 9 is a clean, undistorted sine wave. The second half appears to be a clipped sine wave; we shall talk about this trace in detail later. The trace in Figure 4 is a good example of what happens in intense electric fields; a relatively high frequency noise, probably caused by corona discharge from the rocket, is superimposed on the sinusoidal signal. The corona noise does not obscure the sinusoidal s...

The electric field along the path of an instrumented balloon was closely coupled to the wind profile and to the radar echo structure of a weak thunderstorm over Langmuir Laboratory on July 16, 1975. The balloon ascended at 3.5 m/s into the southern part of the storm, where a stable layer had stopped the cloud's vertical convection at 6.4 km above sea level. At lower altitudes, near the cloud base, the balloon rose past two nearby oppositely charged regions which were associated with a precipitation echo and with an outflow of air from the storm. When the balloon ascended into clear air through the top of the lower cloud at 6.4‐km altitude, its motion indicated a sharp change in wind direction, and its electric field meter showed an abrupt decrease in field intensity, probably from a screening layer at the cloud boundary. Above 7.5 km the balloon encountered a slanted and charged downdraft just before entering the northern part of the storm under its anvil cloud. This downdraft, which had a velocity of about 6 m/s, was a prominent and persistent feature of the cloud's circulation. It held the balloon at a nearly constant altitude of 7.7 km for 10 min while carrying it 3 km toward the center of the storm. When the electric field meter descended, after release from the balloon, it encountered the downdraft a second time, 24 min after its first encounter. Electric field measurements suggest that the downdraft was carrying a negative charge. Our measurements on this storm also contain evidence for vertical transport of horizontal momentum and for a net positive charge in the upper part of the storm.