Flights through the central regions of thunderstorms were made over New Mexico on 6 and 15 August I977 with the ONR/NMIMT Schweitzer aeroplane which carried equipment designed to measure all three components of the electric field, and the charge, Q, and diameter, d, of individual precipitation elements. On the earlier day, information was also obtained with : a rain-gaugenetworksurrounding Langmuir Laboratory; a 3 cm radar; an acoustic system for locating lightning channels; a ground-based field-change meter.The first cell on 6 August produced precipitation at the ground but no lightning. Vertical fields, E,, of up to about 50 kVm-' and precipitation charge densities pp of up to -0.5Cwere recorded within the cloud. The second cell, which grew as the first one decayed, produced 7 lightning strokes in 9 minutes during which time the radar revealed vigorous vertical growth in a narrow zone containing precipitation.Thunder reconstructions showed the acoustic sources for the first flash of this cell to be very near the top of the cloud at an altitude of 10 km a d . The subsequent flashes produced acoustic signals from progressively lower in the cloud. When the radar echo reached its maximum height lightning activity ceased. E. values of up to about SOkVm-' and pp values of down to -1 C km-3 were measured.pp was consistently negative, individual charges being less than f40pC. Q values were within the inductive limit for a thundercloud at breakdown but no systematic relation between Q and d was found.Six penetrations were made through the thundercloud of 15 August, which produced only two lightning strokes. The E, records were indicative of a (k) dipole located near the cloud top, at around -13°C. Fields of up to about lOOkVm-' and p,, values (positive and negative) of around 5Ckm-3 were measured. Q values of up to i250pC were recorded, with charges around i~50 pC being commonly found. No systematic Q-drelation was revealed, and smaller precipitation particles frequently carried charges (positive or negative) in excess of the inductive limit. On both days estimated precipitation rates were of order IOmmh-' and on most occasions the pilot reported precipitation particles to be either 'ice' or 'mixed liquid water and ice'. 1978
SUMMARYFlights through the central regions of thunderstorms were made over New Mexico on 6 and 15 August I977 with the ONR/NMIMT Schweitzer aeroplane which carried equipment designed to measure all three components of the electric field, and the charge, Q, and diameter, d, of individual precipitation elements. On the earlier day, information was also obtained with : a rain-gaugenetworksurrounding Langmuir Laboratory; a 3 cm radar; an acoustic system for locating lightning channels; a ground-based field-change meter.The first cell on 6 August produced precipitation at the ground but no lightning. Vertical fields, E,, of up to about 50 kVm-' and precipitation charge densities pp of up to -0.5Cwere recorded within the cloud. The second cell, which grew as the first one decayed, produced 7 lightning strokes in 9 minutes during which time the radar revealed vigorous vertical growth in a narrow zone containing precipitation.Thunder reconstructions showed the acoustic sources for the first flash of this cell to be very near the top of the cloud at an altitude of 10 km a d . The subsequent flashes produced acoustic signals from progressively lower in the cloud. When the radar echo reached its maximum height lightning activity ceased. E. values of up to about SOkVm-' and pp values of down to -1 C km-3 were measured.pp was consistently negative, individual charges being less than f40pC. Q values were within the inductive limit for a thundercloud at breakdown but no systematic relation between Q and d was found.Six penetrations were made through the thundercloud of 15 August, which produced only two lightning strokes. The E, records were indicative of a (k) dipole located near the cloud top, at around -13°C. Fields of up to about lOOkVm-' and p,, values (positive and negative) of around 5Ckm-3 were measured. Q values of up to i250pC were recorded, with charges around i~50 pC being commonly found. No systematic Q-drelation was revealed, and smaller precipitation particles frequently carried charges (positive or negative) in excess of the inductive limit. On both days estimated precipitation rates were of order IOmmh-' and on most occasions the pilot reported precipitation particles to be either 'ice' or 'mixed liquid water and ice'.
During the summer of 1960, experiments were conducted in Illinois to determine how the electrical potential gradient and space charge above and beneath fair‐weather cumulus clouds depend on the polarity and concentration of the space charge in the air from which they grow. Artificially produced space charge was released into the atmosphere near the ground during convection. Measurements showed that clouds that form in the electrically modified region exhibited significantly larger potential gradient perturbations than otherwise similar clouds forming nearby. When the charge released was negative, the fair‐weather potential gradient over the cloud was enhanced; when it was positive, the potential gradient was decreased or of reversed polarity. Measurements just beneath the cloud base showed that space charge of the polarity released near the ground was being carried up into the center of the cloud and that space charge of the opposite sign was descending around the outer portions of the cloud. The experimental results show that the polarity and intensity of electrification of small nonprecipitating cumulus clouds is determined primarily by the polarity and concentration of the space charge in the air from which they grow. The agreement between the observations and predictions based on the convective electrification process proposed by Grenet and Vonnegut is consistent with the idea that electric charge is being carried by updrafts and by downdrafts as they have suggested.
Ground and airplane measurements of the natural fair‐weather electric potential gradient and space charge over central Illinois during the summer of 1960 are reported. During the night the potential gradient at the surface is typically quite low, and the lower atmosphere is stratified with layers of positive and negative space charge having densities of several hundred elementary charges per cm3. Shortly after dawn, when convection begins, the potential gradient at the earth's surface rises rapidly and the strata overhead disappear. During the day the space‐charge density in the mixing layer is seldom more than 1 elementary charge per cm3. Occasional singularities (outside this region) in the potential gradient and space charge resulting from manmade sources of charge are described.
Artificially produced space charge of positive or negative polarity was released into the atmosphere at a rate of about 1 milliampere from an electrified horizontal wire 14 km long. Operating characteristics of this apparatus are described. Electrical measurements from an airplane show that the charge from the wire mixed rapidly into the lower atmosphere and caused large perturbations in the fair‐weather electric potential gradient and space charge. These perturbations extended downwind 10 km or more. When there was convection, the charge was rapidly carried aloft by thermal updrafts. The artificial charge appears to be a good tracer for micrometeorological studies of atmospheric circulation.
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