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Lightning Initiation in Thunderclouds,
UNIVERSITY OF MANCHESTER INST OF SCIENCE AND TECHNOLOGY (ENGLAND)
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Experiments have been carried out to determine the electric field, E sub c, required to obtain corona from both ice particles and cooling drop-pairs. In the former case it was found that corona currents of about 0.1 microA and above could be obtained from ice particles a few millimetres in length for C sub c approx. 4 x 100,000 Vm for values of temperature and pressure likely to occur in the mid-regions of a thundercloud. These currents were drastically reduced if temperature was below -18 deg C, owing to the reduction in surface conductivity suffered by the ice sample. In the second set of experiments, a pair of water drops, of radii R2.7mm and r0.65mm, collided with a relative velocity of 5.8ms. Values of Ec ranged from approx. 500,000 ms for head-on collisions to approx. 250,000 ms for glancing collisions which produce, momentarily, long liquid filaments. Author
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