Observational evidence for an inside-out substorm onset scenario

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Annales Geophysicae

OSTI ID:960799

Henderson, Michael G ^[1]

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1. Los Alamos National Laboratory

We present observations which provide strong support for a substorm onset scenario in which a localized inner magnetospheric instability developed first and was later followed by the development of a Near Earth Neutral Line (NENL) farther down-tail. Specifically, we find that the onset began as a localized brightening of an intensified growth phase arc which developed as a periodic series of arc-aligned (i.e. azimuthally arrayed) bright spots. As the disturbance grew, it evolved into vortical structures that propagated poleward and eventually morphed into an east-west aligned arc system at the poleward edge of the auroral substorm bulge. The auroral intensification shows an exponential growth with an estimated e-folding time of around 188 seconds (linear growth rate, {gamma} of 5.33 x 10{sup -3} s{sup -1}). During the initial breakup, no obvious distortions of auroral forms to the north were observed. However, during the expansion phase, intensifications of the poleward boundary of the expanding bulge were observed together with the equatorward ejection of auroral streamers into the bulge. A strong particle injection was observed at geosynchronous orbit, but was delayed by several minutes relative to onsel. Ground magnetometer data also shows a two phase development of mid-latitude positive H-bays, with a quasi-linear increase in H between the onset and the injection. We conclude that this event provides strong evidence in favor of the so-called 'inside-out' substorm onset scenario in which the near Earth region activates first followed at a later time by the formation of a near-to-mid tail substorm X-line. The ballooning instability is discussed as a likely mechanism for the initial onset.

• Research Organization: Los Alamos National Laboratory (LANL)
• Sponsoring Organization: DOE
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 960799
• Report Number(s): LA-UR-08-07251; LA-UR-08-7251
• Journal Information: Annales Geophysicae, Journal Name: Annales Geophysicae; ISSN 0755-0685; ISSN ANGED2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BALLOONING INSTABILITY
DATA
DISTURBANCES
EARTH MAGNETOSPHERE
EXPANSION
GROWTH
INJECTION
INSTABILITY
MAGNETIC BAYS
MAGNETOMETERS
PARTICLES