Global ``Sawtooth " Activity in the April 2002 Geomagnetic Storm

Details Global ``Sawtooth " Activity in the April 2002 Geomagnetic Storm Global ``Sawtooth " Activity in the April 2002 Geomagnetic Storm

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsa12a..05r&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SA12A-05

Physics

2704 Auroral Phenomena (2407), 2778 Ring Current, 2784 Solar Wind/Magnetosphere Interactions, 2788 Storms And Substorms

Scientific paper

One of the most interesting aspects of the April 2002 geomagnetic storm was the quasi-periodic geomagnetic activity that we refer to as ``sawtooth" events. Sawtooth events were first identified as an intriguing signature in the LANL geosynchronous energetic particle fluxes showing sharp increases in particle fluxes followed by gradual decreases which repeat roughly every 2-3 hours. The variations are similar to the standard dropout and injection of energetic particles see in isolated substorms. However, unlike isolated substorms, after each injection a new dropout begins immediately, over a broad range of energies, producing the characteristic sawtooth profile. Furthermore the sawtooth signatures are seen at all local times, not just the near-midnight sector. Space magnetometer data show that the dropouts and injections are produced by exceptionally strong stretching and dipolarization of the magnetic field and confirm that the stretching begins immediately after the preceding injection without an intervening recovery phase. However, ENA observations show that these events are true injections of fresh particles and not an adiabatic re-arrangement in response to the field changes. Auroral observations likewise show clear auroral onsets with each sawtooth injection, but those onsets can be embedded in ongoing auroral activity rather than distinct episodes separated by quiet intervals. It is not surprising that sawtooth activity is a subset of geomagnetic storm activity (intervals of large negative Dst). The quasi-periodicity and clear separation of each onset are not, however, characteristic of most geomagnetic storms. Additionally, each individual sawtooth is associated with an increase in the SYM-H component. Sawtooth intervals such as those in the April 2002 storm provide a unique opportunity to deconvolve the effects of quasi-steady and impulsive responses of the magnetosphere. In addition to discussing the magnetospheric response and solar wind driving that produces these interesting sawtooth signatures we discuss the implications for the interpretation of the broad range of geomagnetic responses to the April 2002 storm interval.

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