MIL-HDBK-274A
happen. Thus, by locally compressing the field, there are more likely to be points where the discharge takes place.
4.4.2.4.3 Cloud discharge. Intracloud and intercloud lightning discharges occur between positive and negative cloud charges and have total durations about equal to those of ground discharges (½ second). A typical cloud discharge neutralizes 10 to 30 coulombs of charge over a total path length of 5 to 10 km. Intracloud and intercloud discharges have not been studied as extensively as cloud discharges to ground, and hence much less is known about their detailed physical characteristics. The charge motion for intracloud and intercloud discharges produces electric fields whose frequency spectra have roughly the same amplitude distribution as electric fields produced by cloud-to-ground discharges for frequencies below about 1 kHz and above 100 kHz. Between 1 and 100 kHz, the ground discharge is a more efficient radiator. Energy levels
of near strikes can be sufficiently high to damage electronic equipment, again, depending on the location of the strike. Distant lightning strikes and lightning from one cloud to another will also charge an aircraft. Grounding will not keep these induced charges from accumulating on an aircraft, but will reduce the amount of time needed to bleed off the charge.
4.4.2.4.4 Current waveform parameters. The most important parameters of the current waveform are peak current, rate of rise, total duration, charge transferred, and action integral (see
4.4.2.3.6). The units of action integral are ampere-seconds, which may alternatively be expressed in units of joules per ohm since the action integral is proportional to the energy dissipated in a given resistance (see Figures 4 and 5).
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