Seminars

Lecturer: M. Yamauchi (IRF)
Date: 2009-02-19 10:30
Place: Aniara

Magnetospheric solitary structure maintained by 3000 km/s ions as a cause of westward moving auroral bulge at 19 MLT

M. Yamauchi
Swedish Institute of Space Physics

On 19 May 2002 at around 06:43 UT within a few seconds difference between all four spacecraft, Cluster observed the equatorial signatures of westward surging auroral bulge at 19 MLT. The entire structure covering both the magnetosphere and both the northern and southern ionospheres is moving westward with following sunward propagating signatures with in the equatorial inner magnetosphere: At equatorial inner magnetosphere: (a) sudden rarefaction of equatorial geomagnetic field by 25% together with local diamagnetic current, (b) electric field in the propagation direction up to 8~9 mV/m, (c) duskward ExB convection of He+ rich cold plasma without O+, up to 50 km/s, (d) flux enhancement of medium energy ring current ions with particle speed of about 3000 km/s for all ion species, increased pressure by which balances with the depletion of the magnetic pressure, (e) flux decrease of the other energetic particles beyond the conservation of magnetic moment can explain, and (f) arrival in time-of-flight manner of ionospheric plasma that is accelerated by parallel potential of about 7 kV slightly after the other in-situ signatures. The observations indicate a solitary structure of about 2000 km width in the propagation direction with propagating speed of about 10 km/s sunward. This solitary structure is composed of polarization electric field in the propagation direction and magnetic depletion, and is maintained by flux enhancement of 3000 km/s ions. These ions are the main carrier of the diamagnetic current that caused the magnetic depletion, whereas the polarization is maintained by different behaviors between mainly energetic ions and energetic electrons. The potential drop in the propagation direction (about 10 kV tailward at equator) is the ultimate cause of the field-aligned potential drop (about 7 kV upward). The sunward propagation of this solitary structure caused the sunward propagation of field-aligned potential drop and hence of the auroral bulge.


Created 2009-02-18 11:30:49 by Mats Holmström
Last changed 2009-02-18 11:30:49 by Mats Holmström