Ionospheric effects associated with magnetic disturbances

Abstract

Consideration of ionospheric effects coinciding with magnetic disturbances must, as yet, be qualitative. Discussion in this paper is directed toward elucidating the nature of ionospheric changes coincident with magnetic activity in the temperate and equatorial zones as interpreted from automatic multifrequency ionospheric records. Observations at Kensington (Maryland) during summer are described and illustrated. During summer night, following commencement of a storm, ion‐density of the F ‐ or F 2 ‐regions decreases and height increases. The region loses its smooth horizontal distribution and appears to break up into “clouds” of non‐uniform ion‐density. There is evidence of turbulence in the F ‐region during the disturbance. When a storm begins at night during summer, the F 2 ‐region is observed to separate from the F 1 ‐region immediately at daybreak, or for more severe disturbances to appear first at great heights above the F 1 ‐region with greatly reduced ion‐density. Winter‐night and summer‐night conditions are similar. For moderate magnetic disturbances during the day in winter little ionospheric disturbance is noticed, the ionosphere recovering rapidly to nearly normal conditions after daylight. Penetration‐frequencies remain slightly disturbed during winter day, ranging from a little above normal to below normal depending upon intensity of the disturbance, and the region appears to be thicker than usual. The severe magnetic disturbance of April 16, 1938, is selected for study in connection with equatorial‐zone ionospheric disturbances. It is shown that this ionospheric disturbance can be divided into three main phases. With the advent of the storm the maximum electron‐density of the F ‐region fell by some three orders of magnitude (essentially to zero) in the first hour. This was followed by appearance of an intensely ionized absorbing region at about 85 km from which echoes were weak. After about 45 minutes this region disappeared as suddenly as it had appeared. Virtual heights of the F ‐region then started to rise, first with increasing and then with decreasing ion‐density, until the maximum ion‐density again fell to substantially zero, with the few remaining electrons (about 5000 per cc) being at enormous heights. The surprising thing about these facts is that the ion‐density should fall essentially to zero throughout the stratosphere. The appearance of an absorbing region at low levels at different latitudes is considered in connection with sporadic E ‐region ionization. Dependence of observed changes of radio transmission upon the observed ionospheric effects are considered.