Characterizing the Magnetospheric State for Sawtooth Events

Magnetospheric sawtooth events, first identified in the early 1990's, are named for their characteristic appearance of multiple quasi-periodic intervals of slow decrease followed by sharp increase of proton energy fluxes in the geosynchronous region. The successive proton flux decrease-and-increase intervals have been interpreted as recurrences of stretching and dipolarization, respectively, of the nightside geomagnetic field [Reeves et al., 2003]. Due to their often-extended intervals with 2- 10 cycles, sawteeth occurrences are sometimes referred to as a magnetospheric mode [Henderson et al., 2006]. Studies over the past two decades of sawtooth events (both event and statistical) have yielded a wealth of information on the conditions for the onset and occurrence of sawtooth events, but the occurrences of sawtooth events during both storm and non-storm periods suggest that we still do not fully understand the true nature of sawtooth events [Cai et al., 2011]. In this study, we investigate the characteristic magnetospheric state conditions [Fung and Shao, 2008] associated with the beginning, during, and ending intervals of sawtooth events. Unlike previous studies of individual sawtooth event conditions, magnetospheric state conditions consider the combinations of both magnetospheric drivers (solar wind) and multiple geomagnetic responses. Our presentation will discuss the most probable conditions for a "sawtooth state" of the magnetosphere. ReferencesCai, X., J.-C. Zhang, C. R. Clauer, and M. W. Liemohn (2011), Relationship between sawtooth events and magnetic storms, J. Geophys. Res., 116, A07208, doi:10.1029/2010JA016310. Fung, S. F. and X. Shao, Specification of multiple geomagnetic responses to variable solar wind and IMF input, Ann. Geophys., 26, 639-652, 2008. Henderson, M. G., et al. (2006), Magnetospheric and auroral activity during the 18 April 2002 sawtooth event, J. Geophys. Res., 111, A01S90, doi:10.1029/2005JA011111. Reeves, G. D., et al. (2004), IMAGE, POLAR, and geosynchronous observations of substorms and ring current ion injections, in Disturbances in Geospace: The Storm-Substorm Relationship, Geophys. Monogr. Ser., vol. 142, edited by A. S. Sharma, Y. Kamide, and G. S. Lakhina, pp. 91-101, AGU, Washington, D. C.