HR: 0800h
AN: SM31A-0382    [Abstracts]
TI: External Triggers of Sawtooth Events Identified by Dayside Convection Changes
AU: * Zou, S
EM: sha@atmos.ucla.edu
AF: Dept. of Atmospheric and Oceanic Sciences, University of Californis, Los Angeles, 405 Hilgard Ave. 7127 Math Sciences Bldg. , Los Angeles, CA 90095 United States
AU: Lyons, L
EM: larry@atmos.ucla.edu
AF: Dept. of Atmospheric and Oceanic Sciences, University of Californis, Los Angeles, 405 Hilgard Ave. 7127 Math Sciences Bldg. , Los Angeles, CA 90095 United States
AU: Boudouridis, A
EM: thanasis@atmos.ucla.edu
AF: Dept. of Atmospheric and Oceanic Sciences, University of Californis, Los Angeles, 405 Hilgard Ave. 7127 Math Sciences Bldg. , Los Angeles, CA 90095 United States
AU: Ruohoniemi, J
EM: Mike.Ruohoniemi@jhuapl.edu
AF: Johns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Road , Laurel, MD 20723 United States
AB: Sawtooth events are manifestations of successively occurring substorms during storm time. Energetic particle fluxes at geosynchronous orbit decrease during the growth phase of a substorm and increase at the expansion phase of a substorm. When substorms occur consecutively, the fluxes fluctuate like sawteeth. Solar wind dynamic pressure enhancements during strongly southward IMF and IMF changes which lead to a reduction of convection are two possible triggers of these substorms and thus also of sawtooth flux enhancements. We investigate the frequency of external triggers for sawtooth events based on observations of dayside convection. We use dayside convection observations since onsets of IMF initiated substorms have decreases in dayside convection flow speed, while substorms triggered by dynamic pressure enhancements have increases in dayside convection speed. On the other hand, any events not externally triggered would be expected to not be associated with a change in dayside convection. Events are chosen by the criteria that there is good SuperDARN echo coverage on the dayside. Mid and low latitude H component data are also checked for each substorm event. Dynamic pressure enhancements can cause global H-component increases simultaneously, which is a result of global compression. IMF changes triggered substorm cause increases only on the night side, which results from the substorm current wedge. On the basis of the SuperDARN and H-component data, we suggested that some sawtooth injections are due to dynamic pressure enhancements, some are due to IMF changes, which tend to reduce convection, and others are due to a combination of both. These data are consistent with the general substorm external trigger model.
DE: 2720 Energetic particles: trapped
DE: 2736 Magnetosphere/ionosphere interactions (2431)
DE: 2760 Plasma convection (2463)
DE: 2784 Solar wind/magnetosphere interactions
DE: 2788 Magnetic storms and substorms (7954)
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005