Near earth current meander (NECM) model of substorms

WJ Heikkila*, T Chen, ZX Liu, ZY Pu, RJ Pellinen, TI Pulkkinen

*Tämän työn vastaava kirjoittaja

Tutkimustuotos: LehtiartikkeliLiterature reviewvertaisarvioitu

Abstrakti

We propose that the appropriate instability to trigger a substorm is a tailward meander (in the equatorial plane) of the strong current filament that develops during the growth phase. From this single assumption follows the entire sequence of events for a substorm. The main particle acceleration mechanism in the plasma sheet is curvature drift with a dawn-dusk electric field, leading to the production of auroral arcs. Eventually the curvature becomes so high that the ions cannot negotiate the sharp turn at the field-reversal region, locally, at a certain time. The particle motion becomes chaotic, causing a local outward meander of the cross-tail current. An induction electric field is produced by Lenz's law, E-ind=-partial derivativeA/partial derivativet. An outward meander with B-z>0 will cause E x B flow everywhere out from the disturbance; this reaction is a macroscopic instability which we designate the electromotive instability. The response of the plasma is through charge separation and a scalar potential, E-es=-del phi. Both types of electric fields have components parallel to B in a realistic magnetic field. For MHD theory to hold the net E-parallel to must be small; this usually seems to happen (because MHD often does hold), but not always. Part of the response is the formation of field-aligned currents producing the well-known substorm current diversion. This is a direct result of a strong E-parallel to(ind) (the cause) needed to overcome the mirror force of the current carriers; this enables charge separation to produce an opposing electrostatic field E-parallel to(es) (the effect). Satellite data confirm the reality of a strong E-`parallel to in the plasma sheet by counter-streaming of electrons and ions, and by the inverse ion time dispersion, up to several 100 keV. The electron precipitation is associated with the westward traveling surge (WTS) and the ion with omega (Omega) bands, respectively. However, with zero curl, E-es cannot modify the emf epsilon=closed integralE.dl=-d Phi (M)/dt of the inductive electric field E-ind (a property of vector fields); the charge separation that produces a reduction of E-parallel to must enhance the transverse component E-perpendicular to. The new plasma flow becomes a switch for access to the free energy of the stressed magnetotail. On the tailward side the dusk-dawn electric field with E.J 0 will cause injection into the inner plasma sheet, repeatedly observed at moderate energies of 1-50 keV. This same electric field near the emerging X-line will accelerate particles non-adiabatically to moderate energies. With high magnetic moments in a weak magnetic field, electrons (ions) can benefit from gradient and curvature drift to attain high energies (by the ratio of the magnetic field magnitude) in seconds (minutes).

AlkuperäiskieliEnglanti
Sivut399-414
Sivumäärä16
JulkaisuSpace Science Reviews
Vuosikerta95
Numero1-2
TilaJulkaistu - tammik. 2001
OKM-julkaisutyyppiB1 Kirjoitus tieteellisessä aikakauslehdessä

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