The bimodal magnetosphere and ring current, radiation belt, and tail transducers

It has generally been assumed that a geomagnetic storm is entirely driven by external forces-e.g., solar wind E-y = V-x x B-z, V-x, rho V-x(2) (where the components of the electric field, E, the magnetic field, B, and velocity, V, are given in GSE coordinates)-which would imply that particle injections in the ring current (RC) or outer radiation belts should be highly correlated. However the data from ISTP are showing that the magnetosphere can have at least two very different responses to the same solar wind (SW) conditions: a classic, enhanced RC with Dst response, or a 1000-fold increase in the outer radiation belt MeV electrons (ORBE). August 29, October 14 and 23, 1996 are examples of Dst storms, whereas April 15, 1996 and January 10, 1997 are examples of MeV storms. It is this second response that is so deadly to some geosynchronous spacecraft, whereas geomagnetic storms are categorized by the first response. Neither of these appear to be correlated to the SW conditions driving substorms. Why should the SW energy appear in the radiation belts or the ring current independently? We hypothesize that the RC couples to the electric power available (E-y), the ORBE couple to the mechanical power available (V-x), and the Tail couples to the magnetic energy (B-z) available in the SW. The transducer for RC may be subauroral parallel potentials, the transducer for ORBE may be the cusp, while the Tail substorm transducer is yet a third independent mechanism for extracting SW energy. Evidence for this theory comes from the novel POLAR satellite that traverses the cusp, the plasmasheet and the radiation belts. (C) 2000 COSPAR. Published by Elsevier Science Ltd.