Observations of Natural ELF and VLF Electromagnetic Noises by Using Ball Antennas

Abstract

A simple observing system for the measurements of vertical electric field component of natural ELF and VLF electromagnetic noises by using ball antennas is described. With this system it is possible to measure long traveled natural ELF noises discriminated from natural local noises due to such as atmospheric electric space-charge fluctuations. Some of the typical recorded noises are shown. Observed ELF noises are divided into three characteristic types; "ELF flash", "ELF burst" (N-and Q-types), and "ELF continuous". ELF flashes originate from the lightning discharges in the area within about 1, 000 km from the observing station. Occurrences of ELF bursts are more frequent in the daytime than in the nighttime, and are characterized by sudden increase at the time of local sunrise, suggesting the related mechanism of their generation to the solar position relative to the earth. N-type bursts are followed by VLF noises. Source distances of these bursts which are followed by tweek-type atmospherics in the night are estimated to be in the range from 2, 500 km to 5,000km. Q-type bursts often show clear oscillations of the frequencies of Schumann resonances. The daily variations of the mean amplitude of "ELF continuous" which composes the background noises are quite similar to the daily variations of the world thunderstorm activity.

Electromagnetic radiations from shallow earthquakes observed in the LF range.

“…The electric field generated from small size fractures in the granite sample was measured using ball antennas (OGAWA et al, 1966) as a sensor. Electromagnetic waves with predominant spectral peaks in the ELF and VLF ranges were recorded and analyzed.…”

Comparison of the Schumann resonance parameters in horizontal magnetic and electric fields according to observations on the Kola Peninsula

“…The wave trains after extremely strong strokes exceed the background ELF. For the first time they were distinguished and examined by Ogawa et al [1966]. To define this phenomenon, the authors coined a new term ''Q burst,'' which we will also use.…”

“…To define this phenomenon, the authors coined a new term ''Q burst,'' which we will also use. From Q burst damping, Ogawa et al [1966] estimated the distance from the observation point to the source as 2500 -5000 km. Sentman [1989] continued the study of these waves.…”

Schumann Resonances and Worldwide Thunderstorm Activity

“…During the period from February, 1967, to January, 1968, the electric vertical component of natural ELF electromagnetic noises was measured in Kyoto (location: 3501'N, 13547'E) by using a ball antenna (Ogawa, Tanaka, Miura, and Yasuhara, 1966). Simultaneous measurements of the electric horizontal NS and EW components were done at Aso (location:…”