A new model of magnetic storms and aurorae

Abstract

To explain the sudden commencement (SC) of magnetic storms, the reverse sudden commencement (SC*), and pre‐SC disturbances, we invoke the following model: The solar eruption produces a shock wave which arrives at the Earth 22‐34 hours later. Highvelocity particles having a smaller interaction precede the shock wave and cause the pre‐SC bay‐like disturbances at high latitudes. The shock wave itself is retarded by the body forces produced by the geomagnetic field, but speeds up as it enters the auroral zones. In pushing out lines of force, it creates the polar SC* events. Charge separation in the shock wave produces the driving force for the SC currents, which flow in the atmosphere (in accordance with Vestine's analysis). The storm decrease is produced by the high‐velocity particles following the shock wave (up to nine hours later) which enter because of field perturbations into the normally inaccessible Störmer regions around the dipole. Here they are trapped and will drift, producing the ring current which gives rise to the storm decrease. Particles with a small pitch angle, however, can reach the Earth's atmosphere and contribute to aurora, the airglow, and ionospheric ionization. These particles are replenished by perturbations produced by solar influences having a 27‐day recurrence. Many other particles are absorbed or scattered out of the trapping regions so that their number diminishes rapidly in a day or so, as does the magnetic‐storm decrease. The model thus attempts to explain for the first time the cause of the SC*, the atmospheric nature of SC, the delay between SC and the main phase, and the formation and decay of the ring current. A by‐product is auroral‐particle acceleration by a Shockwave. New experimental tests are suggested by the model: (a) Acoustic observations with balloons to look for the shock wave penetrating into the atmosphere in the auroral zones, (b) Observations with rockets or satellites to establish the location of the SC and main‐phase currents, (c) Measurements of the nature and energy of the auroral particles.