Variations of ULF-VLF electric fields in the external ionosphere over powerful typhoons in Pacific Ocean Original Research Article

The results of the preliminary studies of spatial and spectral characteristics of the ULF-VLF electric field absolute values in the topside ionosphere over the Pacific Ocean aquatory at h = 1500–2500 km in the daytime and at h = 550–700 km in the nighttime in September 1990 are presented. The registration results of the E component of the field by the narrow-band filters at frequencies of 8, 20, 33, 50, 75, 150, 225, 433, 623, 970 Hz, 9.6 and 15 kHz installed on board the Intercosmos 24 satellite were used. The spectral distribution of the E component of the field both in the day and night time qualitatively agrees with the propagation theory of the ULF-VLF wave whistler mode through the ionosphere, but the anomalously high field values in the daytime contradict this theory and the experimental data available. This may be related to giant lightning discharges over typhoons and amplification of the signal by focusing of ray trajectories at the daytime and defocusing them at the nighttime near equatorial anomaly.