Lightning discharges were investigated with high time‐resolution equipment on both electric‐field and electric‐field‐change meters. The analysis of the electrical records reveals that the late stages of intracloud discharges are very similar to those of cloud‐to‐ground discharges during the periods between successive return strokes (junction process) and during the period after the last return stroke (final process). In contrast, the initial portion of the field change of an intracloud discharge bears little or no resemblance to the initial portion of the leader field change of a discharge to ground. It is suggested that the difference in the initial breakdown characteristics results from variations in the relative populations of water drops and ice particles as they affect the internal impedence of the region of cloud where breakdown occurs. The difference in the initial field‐change characteristics of intracloud and cloud‐to‐ground discharges is so distinct that from the first 10 msec of the electric‐field‐change record one can predict with over 95 per cent certainty whether a discharge will reach ground or remain within the cloud.

About 200 excellent photographs of cloud‐to‐ground discharges, taken with a newly designed rotating‐film camera, were obtained from very active thunderstorms in 1959 and 1960. The electric‐field changes and luminosity variations of the photographed discharges were recorded simultaneously on two oscilloscopes having different time resolution. Fifty per cent of the multiple‐stroke flashes, constituting about 90 per cent of cloud‐to‐ground flashes, are found to involve at least one stroke which is followed by very long continuing luminosity lasting for 40 to 500 msec. This continuing luminosity contains a number of relatively brighter components essentially the same as the M components which are known to follow some strokes having very short time intervals. The analysis of the electric field associated with the continuing luminosity reveals that, during the luminous period, negative charge from the cloud flows to ground continuously. The surges of current (M components) during the continuing luminosity are associated with the small rapid field changes (K changes), and the time interval between M components is statistically the same as that between the K changes generally observed during the interstroke and final period of cloud‐to‐ground flashes. During the period of continuing luminosity, the lightning channel maintains a level of conductivity which is high enough to support a momentary current increase without involving the leader process. After the channel loses its luminosity, it maintains a lower level of conductivity for 7 to 100 msec, and a subsequent stroke during this period can also follow the same channel. When a longer time elapses (>100 msec), a subsequent stroke, if any, takes a different channel with a new stepped leader.

The winter thunderclouds that frequently visit the southeastern coastal area of the Japan Sea were investigated by the field work, operating radars, the sferics direction‐finder system, and the field‐mill network. The clouds take the dipole electrical structure at their developing stage and then take the tripole structure at the mature stage. However, the period covering both dipole and tripole structures is very short (usually less than 10 min in early or late winter and less than several minutes in midwinter), because the graupel particles that carry the main negative charge and the lower positive charge do not stay stationarily in the clouds but fall off rapidly. For the remainder of the period of cloud duration, which lasts relatively long, the positive charge predominates in the clouds. The grade of charge separation and lightning activity is restricted by the altitude of −10°C temperature level. When the altitude is lower than 1.8 km, the clouds exhibit weak or no lightning activity. When it is lower than 1.4 km, the clouds exhibit neither natural lightning discharge nor tripole electrical structure.

Results of measurements and calculations of the charge brought to earth by individual strokes and continuing currents from lightning flashes in New Mexico thunderstorms are presented. Hybrid flashes, which contain at least one long‐continuing current interval, lower approximately twice as much charge as do the discrete flashes. The average value of negative charge lowered to earth in hybrid flashes is 34 coulombs compared with 19 coulombs for the discrete flashes, a difference accounted for by the presence of the long‐continuing (>40 msec) current intervals of average duration 150 msec, during which time an average charge of 12 coulombs is lowered to earth. The continuing currents vary over a relatively narrow range from a minimum of 38 amp to a maximum of 130 amp. Some aspects of the J‐change measurements of Malan and of Pierce are reexamined in the light of the magnitude and frequent occurrence of the continuing currents. It is concluded that earlier measurements of J changes for distances greater than 50 km must be interpreted as having been produced by the continuous flow of negative charge to earth instead of by the upward movement of positive charge contained within the cloud.

Simultaneous records of electrostatic field, field change, and radiation at 420 and 850 Mc/s were obtained for lightning flashes from 10 to 30 km distant. At these frequencies, the principal source of radiation appears to be associated with the development of streamers in the breakdown process. Strong radiation is associated with the stepped and dart leaders and with the K changes in both the intracloud and cloud‐to‐ground flashes. The return stroke does not always produce detectable radiation at these frequencies; in about 50 per cent of the cases the radiation is absent or appears only after a delay of 60 to 100 μsec after the onset of the return stroke. This delay is attributed to the absence of radiation associated with breakdown streamers until the return stroke reaches the top of the channel within the cloud. A cessation of the dart leader radiation of 50 to 150 μsec before the return stroke also suggests that the radiation occurring during the dart leader phase is produced primarily within the cloud.