The roles of the northsouth component of the interplanetary magnetic field on largescale auroral dynamics observed by the DMSP satellite
Abstract
An extensive study of DMSP photographs and the simultaneous interplanetary magnetic field data suggests that the quantity defined by S=∫ ^{τ}_{0}(Ф _{D}  Ф _{N})dt has a fundamental importance in substorm processes, where Φ _{D} and Φ _{N} denote the production rate of merged (or open) field lines along the dayside Xline and of reconnected (or closed) field lines along the nightside Xline, respectively; t = 0 is measured from the time when the B_{z} component begins to decrease after a prolonged period of a large positive B_{z} value. It is shown, first of all, that substorms occur so long as S > 0, regardless of the sign of the B_{z} component and its changes (namely, the southward and northward turnings) and of its time derivative as well. Secondly, the intensity of substorms is proportional to S^{2}. By introducing the quantity S, the recent confusion of the problem of the roles of the northsouth component of the interplanetary magnetic field on substorm processes can be removed. Since S is equal to the amount of the open magnetic fluxes at a time reckoned from t = 0, it is proportional to ( A_{1}  A_{0}), where A_{0} denotes the minimum polar cap area (namely, the area bounded by the minimum auroral oval) and A_{1} the polar cap area at an arbitrary time t. Therefore, substorms can occur whenever the auroral oval is larger than its minimum size. Further, an intense substorm tends to occur along a large oval. The quantity S can also be considered as an excess flux, and thus the substorm can be considered as a process by which the magnetosphere tends to remove sporadically the excess energy associated with S.
 Publication:

Planetary and Space Science
 Pub Date:
 October 1975
 DOI:
 10.1016/00320633(75)900306
 Bibcode:
 1975P&SS...23.1349A
 Keywords:

 Auroras;
 Geomagnetism;
 Interplanetary Magnetic Fields;
 Magnetic Effects;
 Dynamic Characteristics;
 Magnetic Flux;
 Planetary Magnetic Fields;
 Satellite Observation;
 Geophysics