地電流の雷雨による説明

抄録

As the measurement of the earth current has not so small difficulties and only a few stations are constantly recording the phenomena, it is impossible to investigate fully the distribution of the earth current over the globe. But roughly speaking, in an average state, the earth current is directed towards the equator in the meridional plane of the globe. The variation in its east-west component is more conspicuous than that in its north-south component. To explain these states of the earth current various theories have been proposed without a full success. In this paper the author considers the rôle of the thunderstorm upon the earth current and shows some relations existing between them in its average state. Owing to the luck of data available, this may perhaps be mere a suggestion in the explanation of the earth current.
Recent investigations of the polarity of thunderstorm by Klydnograph show us that the bottom of thundercloud has a negative charge making under it the great potential gradient opposite to the fine weather potential gradient. This state necessarily causes the upward electric current of considerable strength by the point discharge from the tops of trees, grasses and even sea waves. Though the duration of the thunderstorm is very small compared with the total hour of an year, the greatness of the point-discharge electric current contributes most strikingly to the average state of the vertical electric current near the earth's surface.
In the equatorial region the earth's surface receives an excess of negative charge by the disturbed weather, while an excess of positive charge at the polar caps. This conclusion is mainly due to the unequal distribution of thunderstorm over the globe, hence of the upward point-discharge electric current. (Table 2) Then the unbalanced distribution of the charge over the globe should contribute to the occurence of the electric current in the semi-conducting medium, the earth, in order to make the charges distribute equally over the globe. This is the reason proposed by the present author of the generation of the earth current. The average state of the earth current coincides in its direction and in its variation (very roughly in its intensity, too) with the observations.
Hence if the earth current is mainly due to the thunderstorm activity, in its diurnal variation, too, this relation should be hold very approximately. Namely the earth current must point to the most thundry region at hours which are very favourable for the occurence of thunderstorm at that region. The observations of the earth currents at Kakioka and Toyohara Observatories show us that the earth currents point generally to the tropical islands such as Java, Borneo etc and the direction changes gradually westwards as the time advances from 9h. (1. m. t.) to 17h. indicating the possibility of the existence of the mutual relations between the earth current and the thunderstorm activity in the tropical island (Fig. 3)