VERY-LOW LATITUDE WHISTLERS AND THE EFFECT OF EARTH-IONOSPHERE WAVE-GUIDE PROPAGATION

When a sonogram of the nighttime whistlers observed in Wuchang, China, at a low latitude (at a geomagnetic latitude of 19.4 degrees N) was studied in detail, whisker-type spectral components were observed, which may be due to the waveguide propagation effect of the second- and third-order modes, in the spectra of intense whistlers accompanied by echo trains. By applying the field analysis direction-finding method to this part, the propagation characteristics are derived and the results exhibited a tendency identical to that of the characteristics of tweek atmospherics. It was found that the whistlers transmitted through the ionosphere at a very low latitude in Zhanjiang (geomagnetic latitude of 10.0 degrees N) and exhibited an extremely rare waveguide mode propagation after subionospheric propagation of over approximately 1000 km.