TY - JOUR

T1 - Magnetospheric and auroral activity during the April 18, 2002 sawtooth event.

AU - Henderson, M. G.

AU - Reeves, G. D.

AU - Skoug, R.

AU - Thomsen, M .F.

AU - Denton, Michael H.

AU - Mende, S. B.

AU - Immel, T. J.

AU - Brandt, P. C.

AU - Singer, H.

N1 - Copyright (2006) American Geophysical Union.

PY - 2006

Y1 - 2006

N2 - We examine the 18 April 2002 sawtooth event. We find that the strong magnetic field dipolarizations observed in association with each tooth are not global in occurrence but are rather confined to the nightside. In addition, we find that the flux increases are not globally dispersionless. Instead, each tooth is associated with a nonglobal, but wider-than-usual, dispersionless injection region that is consistent with the high Kp versions of the standard injection boundary model (which places the entire nightside segment of geosynchronous orbit tailward of the injection boundary for values of Kp above about 5). We also find evidence that at least one of the teeth was likely triggered by a pressure pulse. The auroral distribution shows a repeatable evolution in which a wide double-oval configuration gradually thins. Following this, a localized substorm-like brightening in the dusk to midnight sector occurs on the lower branch of the double oval which subsequently expands rapidly poleward and azimuthally. A new expanded double oval configuration emerges from this expansion phase activity and the cycle repeats itself for the duration of the sawtooth event. The observations presented give considerable support to the contention that sawtooth events are actually sequences of quasi-periodic substorms. We suggest that sawtooth events can be viewed as a magnetospheric mode similar to Steady Magnetospheric Convection intervals (SMCs) except that for sawtooth events, the flow of energy from the solar wind into the magnetosphere becomes too large to dissipate without the periodic occurrence of substorms. We further suggest that the quasi-periodicity arises because the magnetosphere may only become susceptible to external or internal triggering after it has been driven beyond a stability threshold. This hypothesis can account for the existence of more potential external triggers (in the interplanetary magnetic field or solar wind) than teeth in that the magnetosphere may be selectively responsive to them.

AB - We examine the 18 April 2002 sawtooth event. We find that the strong magnetic field dipolarizations observed in association with each tooth are not global in occurrence but are rather confined to the nightside. In addition, we find that the flux increases are not globally dispersionless. Instead, each tooth is associated with a nonglobal, but wider-than-usual, dispersionless injection region that is consistent with the high Kp versions of the standard injection boundary model (which places the entire nightside segment of geosynchronous orbit tailward of the injection boundary for values of Kp above about 5). We also find evidence that at least one of the teeth was likely triggered by a pressure pulse. The auroral distribution shows a repeatable evolution in which a wide double-oval configuration gradually thins. Following this, a localized substorm-like brightening in the dusk to midnight sector occurs on the lower branch of the double oval which subsequently expands rapidly poleward and azimuthally. A new expanded double oval configuration emerges from this expansion phase activity and the cycle repeats itself for the duration of the sawtooth event. The observations presented give considerable support to the contention that sawtooth events are actually sequences of quasi-periodic substorms. We suggest that sawtooth events can be viewed as a magnetospheric mode similar to Steady Magnetospheric Convection intervals (SMCs) except that for sawtooth events, the flow of energy from the solar wind into the magnetosphere becomes too large to dissipate without the periodic occurrence of substorms. We further suggest that the quasi-periodicity arises because the magnetosphere may only become susceptible to external or internal triggering after it has been driven beyond a stability threshold. This hypothesis can account for the existence of more potential external triggers (in the interplanetary magnetic field or solar wind) than teeth in that the magnetosphere may be selectively responsive to them.

KW - sawtooth magnetosphere storm substorm DCS-publications-id

KW - art-777

KW - DCS-publications-personnel-id

KW - 123

U2 - 10.1029/2005JA011111

DO - 10.1029/2005JA011111

M3 - Journal article

VL - 111

SP - 1

EP - 15

JO - Journal of Geophysical Research

JF - Journal of Geophysical Research

SN - 0148-0227

IS - A01S90

ER -