TY - JOUR

T1 - Sporadic plasma sheet ion injections into the high-altitude auroral bulge

T2 - Satellite observations

AU - Sauvaud, JA

AU - Popescu, D

AU - Delcourt, DC

AU - Parks, GK

AU - Brittnacher, M

AU - Sergeev, V.A.

AU - Kovrazhkin, RA

AU - Mukai, T

AU - Kokubun, S

PY - 1999/12/1

Y1 - 1999/12/1

N2 - We report on a new feature of auroral substorms, namely, the sporadic though recurrent injections of magnetospheric ions throughout the auroral bulge. These injections are interpreted as time of flight dispersed ion structures (TDIS). Our analysis builds on a combination of measurements from Interball-Auroral, from UV imagery onboard Polar, from ground magnetometers, and also from observations on Geotail and from geostationary spacecraft. Backward tracing of ion trajectories from Interball-Auroral orbit using realistic three-dimensional magnetic and electric field models indicates that the injection region can extend over a wide range of radial distances, from similar to 7-40 R-E in the nearly equatorial magnetosphere. Both hydrogen and oxygen ions are shown to be injected toward the Earth's upper ionosphere. At Interball altitudes we find that ion injections are associated with two types of low-frequency torsional oscillations of the magnetic field: (1) shear Alfven waves with a period of a few minutes with the highest amplitude near the bulge front and decreasing amplitude at lower latitudes and (2) higher-frequency shear Alfven waves of the P1B type, strictly restricted to the poleward boundary of the surge, with a characteristic period of similar to 40 s. The systematic observation of sporadic TDIS during the auroral bulge expansion leads us to conclude that the same physical process is at work throughout the midtail. We also show that ion injections are detected well inside the bulge, which suggests that the injection fronts propagate from the outer to the inner magnetosphere over large distances. This topic is more extensively studied by Sergeev et al. [1999]. We also show that the poleward boundary of the surge is associated with a prominent outflow of ionospheric H+ and O+. These ions in the hundred of eV to the keV range are heated perpendicularly to the local magnetic field and subsequently transported into the magnetotail. The expanding auroral bulge thus forms a significant source of ionospheric ions for the midtail magnetosphere.

AB - We report on a new feature of auroral substorms, namely, the sporadic though recurrent injections of magnetospheric ions throughout the auroral bulge. These injections are interpreted as time of flight dispersed ion structures (TDIS). Our analysis builds on a combination of measurements from Interball-Auroral, from UV imagery onboard Polar, from ground magnetometers, and also from observations on Geotail and from geostationary spacecraft. Backward tracing of ion trajectories from Interball-Auroral orbit using realistic three-dimensional magnetic and electric field models indicates that the injection region can extend over a wide range of radial distances, from similar to 7-40 R-E in the nearly equatorial magnetosphere. Both hydrogen and oxygen ions are shown to be injected toward the Earth's upper ionosphere. At Interball altitudes we find that ion injections are associated with two types of low-frequency torsional oscillations of the magnetic field: (1) shear Alfven waves with a period of a few minutes with the highest amplitude near the bulge front and decreasing amplitude at lower latitudes and (2) higher-frequency shear Alfven waves of the P1B type, strictly restricted to the poleward boundary of the surge, with a characteristic period of similar to 40 s. The systematic observation of sporadic TDIS during the auroral bulge expansion leads us to conclude that the same physical process is at work throughout the midtail. We also show that ion injections are detected well inside the bulge, which suggests that the injection fronts propagate from the outer to the inner magnetosphere over large distances. This topic is more extensively studied by Sergeev et al. [1999]. We also show that the poleward boundary of the surge is associated with a prominent outflow of ionospheric H+ and O+. These ions in the hundred of eV to the keV range are heated perpendicularly to the local magnetic field and subsequently transported into the magnetotail. The expanding auroral bulge thus forms a significant source of ionospheric ions for the midtail magnetosphere.

KW - SUBSTORM CURRENT WEDGE

KW - MAGNETOTAIL CURRENT SHEET

KW - TAIL CURRENT DISRUPTION

KW - SINGLE-PARTICLE ORBITS

KW - NEAR-EARTH MAGNETOTAIL

KW - MAGNETOSPHERIC SUBSTORMS

KW - GEOMAGNETIC-ACTIVITY

KW - EXPERIMENT ONBOARD

KW - MAGNETIC-FIELD

KW - DYNAMICS

U2 - 10.1029/1999JA900293

DO - 10.1029/1999JA900293

M3 - статья

VL - 104

SP - 28565

EP - 28586

JO - Journal of Geophysical Research: Biogeosciences

JF - Journal of Geophysical Research: Biogeosciences

SN - 0148-0227

IS - A12

ER -