Modeling of atmospheric radio noise near thunderstorms


  • Taketoshi Nakai


A model of atmospheric radio noise produced by a near thunderstorm is presented to give a physical interpretation to the properties of the fields in terms of the peak amplitude distributions of received impulses at the input of a narrow-band receiver. In connection with the model, propagation over a short distance from any discharge inside the thunderstorm and the statistics of varying peak currents of return strokes and K changes are examined, and two different expressions, one expressing a lognormal distribution only for return strokes and the other a combination of two different lognormal distributions for the coexistence of return strokes and K changes, are presented, both of which are available in calculating the respective part of the peak amplitude distribution. The emphasis is on the variation in the shape of the distribution with the distance to the thunderstorm. Comparisons have been made between calculated distributions and evvelope crossing rate distributions (CRD's) at the output of the receiver. Comparisons have been found to be good for a frequency of 3 kHz in the high-amplitude range of measured CRD's, which is nearly equal to the corresponding peak amplitude distribution at the input of the receiver. Further application of the model is shown to be appropriate to higher frequencies, 50 kHz and 90 kHz, on the basis of the observed behavior of CRD's.