Diurnal variation of cosmic radiation intensity produced by a solar wind

Abstract

Abstract Starting from the concept that the solar magnetic field is twisted into an Archimedes spiral which, on the average, co-rotates with the sun, it is shown that a diurnal variation in cosmic ray intensity is produced. Cosmic rays tend to be entrapped in the co-rotating spiral magnetic field; the guiding centres of such particles move past the earth with a velocity of several hundred km s . (The guiding centre velocity vector is a function of the angular velocity of the sua and the velocity of the solar wind.) It is shown that relativistic effects caused by this guiding centre motion can produce a diurnal variation in cosmic ray intensity. Because the amplitude and direction of maximum intensity depend on the solar wind velocity, a measurement of the diurnal variation of cosmic ray intensity allows an estimate to be made of the solar wind velocity. On the basis of presently available cosmic radiation data, it is concluded that the solar wind velocity is usuarfy of the order of 300 km s and seldom falls below 100 km s , even at sunspot minimum.