A study of relationships between the aurora borealis and the geomagnetic disturbances caused by electric currents in the ionosphere

Abstract

In high latitudes, magnetic disturbances attributable to intense electric currents in the upper atmosphere are known to occur simultaneously with visible aurora. With few exceptions past investigations have merely revealed statistically that the degree of magnetic disturbance is proportional to the intensity of auroral activity. In the research reported here, magnetic records and auroral observations from College (Fairbanks), Alaska have been studied in detail to determine the manner in which these phenomena are related. It is found that the relationships are quite definite and that practically all, if not all, disturbances may be represented in terms of two closely related patterns describing sequences of auroral activity which accompany positive and negative bay disturbances. Disturbances may appear extremely complicated due to repetition and overlapping of bays; examples are given to illustrate that these disturbances can be easily separated into individual bays by examining the sequence of auroral activity. A discontinuity in auroral activity occurs simultaneously with the reversal in direction of electric currents during the midnight hours; this feature indicates a dependence between the aurora and the electromotive force and thus contradicts a common opinion that aurora merely augments the conductivity. The pattern of behavior during magnetic storms preceded by sudden commencements is the same as on other nights. A preliminary analysis suggests that sudden commencements, reported on a world-wide scale, may be related to sudden changes from homogeneous to rayed aurora in the auroral zone. Special attention is given to: (1) the spatial association of aurora and electric currents, (2) a previously undescribed interval of +[Delta]H disturbance following negative bays, (3) auroral pulsations and movements, and (4) the repetition of similar features on consecutive nights. Theories and suggestions as to the cause of aurora and auroral zone currents are examined with reference to the present study.