Some polarization characteristics of Pc 3--5 micropulsations observed at Colombo, Ceylon

Some polarization characteristics of geomagnetic micropulsations in the period range 20–600 sec recorded about 200 km south of the geomagnetic equator in Colombo, Ceylon, at a distance of about half a mile from the western coastline of Ceylon, which runs approximately N-S, have been studied. It is found that the magnetic vector of the micropulsations lies almost entirely in the plane of the magnetic meridian and that the inclination of the vector to the horizontal increases as the period increases. This increase in inclination with period is very gradual at nighttime but is much more pronounced during daytime. The buildup and decay of ΔZ / ΔH during daytime seem to follow the buildup and decay of the E region of the ionosphere. It is suggested that these polarization characteristics support the view that the micropulsations observed in Colombo are the induction effects of fluctuating current systems in the ionosphere flowing in the E-W direction in the region of the geomagnetic equator, the currents being in the E layer during daytime and in the F layer at nighttime.