The location of thunderstorms by a single-station high-frequency ranging technique

Abstract

By observing the signal radiated by a lightning discharge on a number of frequencies in the high-frequency band, and measuring the maximum usable frequency, the range of the source may be found from a knowledge of the ionospheric conditions. By measuring simultaneously the direction of arrival of the signal, using a low-frequency cathode-ray direction finder operating on 10 kc/s, the position of the storm is determined. A preliminary investigation of the technique, reported in a previous paper, has now been extended by a more thorough investigation of the influence of ionospheric conditions and by improvements in the method of observation. It is necessary to know which layer is controlling the propagation and, in the case of F2, to know also the height and thickness of the layer. Outside the sunset and sunrise periods, the E and F1 conditions may be calculated sufficiently accurately from the zenithal angle of the sun; the F2 conditions are derived from the predicted critical frequencies and MUF factors. Range measurement appears to be impossible when propagation is controlled by sporadic E ionization. Observations made during the summer of 1954 are compared with the thunderstorm positions given by the Meteorological Office network of direction finders. Some of the measurements wore made in conjunction with backscatter observations for determining the ionospheric conditions. It is concluded that the system provides a possible technique for the location of thunderstorms within 500–2000 km of a single observing station, for about 70% of the time. Apart from four months around midwinter, it is essential to have backscatter equipment to provide continual monitoring for Es propagation. An accuracy of 10% in range should be obtained at 1000 km under good conditions.