Abstract
The authors demonstrate by analysing data for 1960, 1961 and 1962 that daily planetary index of geomagnetic disturbance Kp≥25 occurs about as often with decreases (dI/dt<0) as with increases (dI/dt>0) of daily mean intensity of galactic cosmic rays measured on the earth.
They have studied the association of these two types of Kp≥25 epochs and of International Quiet Days with the central meridian passage of long lasting zones of activity in the corona at the solar equator.
The authors suggest that high Kp is caused by two distinct types of interplanetary conditions, (a) the passage of a corotating shock front or a radially advancing blast wave, and (b) the emergence of the earth from a cavity as proposed by Sarabhai considering the consequences of nonuniformity of solar wind velocity.
The occurrence of an International Quiet Day is related to c. m. p. of the intermediate point of declining intensity on the trailing edge of a bright coronal zone which should produce a cavity (a region of reduced plasma density and weak magnetic field) where slow plasma does not catch up with fast plasma in front of it.
