An Investigation of the Lightning Discharge with the Magnetograph

Abstract

The high sensitive quick running magnetograph records the sudden change of magnetic field strength at the instant of lightning discharge. The author of the present paper solved the equation of motion of the suspended magnet of the magnetometer with a control magnet, with the initial velocity determined by the sudden change of magnetic field at the instant of lightning discharge. The relation between the maximum swing Φ of the magnet and the electric quantity Q of the discharge is expressed by where M is the magnetic moment of the suspended magnet, D the damping coefficient of the moving system, K the constant determined by the position and length of the discharge. M, D and other constants have been determined for our magnetometer.
The author has examined the horizontal force magnetogram of Aug. 26th 1934. On this day the thunderstorm associated by a discontinuity-line swept over Toyohara, Sakhalin, from SW to NE, and _??_used 46 cases of the sudden change of magnetic field. When the thunder heard from west quadrant almost all the change is negative. On the contrary when the thunder heard from east most change is positive. From this we can see this thundercloud has the polarity of C. T. R. Wilson's type. We have five cases of which both the lightning and thunder were observed. The electric quantity of the lightning discharge was calculated from maximum swing of the suspended magnet, assuming plausiblly the position and length of the discharge in several ways, knowing the distance of the discharge by the time interval of lightning and thunder. The result was that the electric quantity of the discharge ranged from 20-30 to 200-300 coulombs. This is several times larger than that observed by C. T. R. Wilson in England, and B. F. J. Schonland and J. Craib in south Africa with the capillary electrometer.