Studies and Applications of Geomagnetic Micropulsations

Abstract

A series of mainly Pc3 micropulsation data is examined in terms of diurnal variations and Kp dependences. Within the statistical nature of the activity, characteristic features are observed and established for the horizontal field. The amplitude is linearly dependent on Kp and has a diurnal variation with a maximum value at 9-l2 hrs LT. The sense of rotation is right-handed in the early morning and left-handed in the afternoon, the axis of symmetry being 10-22 hrs LT. However, the daytime location of equal probability of both senses is at 7 l/4 hrs LT, as a greater proportion of the ellipses are left-handed. This time is dependent on Kp. The direction of the ellipse changes from being between 100º and 140º E of N in the early morning to being between l30º and l70º E of N in the afternoon. In the transition (7-10 hrs LT) all angles are possible but angles between 80º and l20º E of N occur more frequently. The ratio of the minor and major axes has a most probable value of .6 to .4 but this is superimposed on the diurnal variation which gives the ratio a greater probability of being circular in the morning and linear in the afternoon. The period of the Pc's during the day (6-15 hrs LT) has a mean of 31.3 seconds but longer periods are observed outside this region giving a slightly U-type diurnal variation. The periods are longer in winter than in summer and decrease with increasing Kp. The period is related to the size of the magnetosphere and its linear compression while the polarization is associated with the solar wind's interaction with the magnetosphere and poloidal mode propagation. The micropulsations are also applied to the magnetotelluric method of probing the earth’s interior and a highly resistive substratum is found.