Storm Dependence of Occurrence Probability and Spatial Distribution of Upstream Events: Its Implication for Their Origin

Details Storm Dependence of Occurrence Probability and Spatial Distribution of Upstream Events: Its Implication for Their Origin Storm Dependence of Occurrence Probability and Spatial Distribution of Upstream Events: Its Implication for Their Origin

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm71a0589k&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SM71A-0589

Physics

2700 Magnetospheric Physics, 2731 Magnetosphere: Outer, 2778 Ring Current, 2788 Storms And Substorms

Scientific paper

Increases of high energy (> 50 keV) particle flux, called upstream events, have been reported but their origin is yet to be identified. We examined how upstream events depend on geomagnetic storms, by using ion flux data acquired by the ICS sensor of the EPIC instrument on board the Geotail spacecraft. In an analysis using ion data from the EPIC P3 channel (77.3 keV - 107.4 keV), we identified upstream events to be flux enhancements by a factor of greater than 100 occurring in less than 10 minutes in the upstream region defined by XGSE>0 and 15 < √ XGSE2+YGSE^2 < 35 Re. Observations are sorted into four radial distance bins and eight local time bins, resulting in each mesh has a radial size of 5 Re and a local time of 1.5 hours. We calculated the occurrence probability, which is the total duration of events divided by traveling time of the satellite, in each mesh. We also analyzed its dependence on the SYM-H index, which is thought to indicate a geomagnetic storm activity. The probability was about 0.05 regardless of satellite location when the SYM-H was larger than zero (no storm). By contrast, the probability reached 0.2 to 0.3 in the dawnside and about 0.1 in the duskside when the SYM-H was below -30 nT (storm time). This dawn-dusk asymmetry was stronger than that derived from all events. We have also examined carbon-nitrogen-oxygen (CNO) ions detected by M3 channel (221.4 keV - 275.2 keV) during the upstream events. Plots of M3 channel data show that background flux of CNO ions was less than one count in the upstream region. We consider ion counts more than three as a flux enhancement of CNO ions, because the lower limit of the uncertainty for three counts (2.42) is larger than the upper limit of the uncertainty for one count (2.00). The enhancement was observed in almost all the upstream events. The rate of detecting the enhancement reached more than 80 %. These statistical results indicate that particles of magnetospheric origin are observed more frequently in the upstream region when a storm occurs in particular. We conclude that energetic particles can leak out of the magnetosphere and travel toward the dawnside of the upstream region when a storm occurs. We propose that this leakage process is a possible decay mechanism of the storm-time ring current.

Affiliated with

Also associated with

No associations

Rating

Storm Dependence of Occurrence Probability and Spatial Distribution of Upstream Events: Its Implication for Their Origin does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Storm Dependence of Occurrence Probability and Spatial Distribution of Upstream Events: Its Implication for Their Origin, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Storm Dependence of Occurrence Probability and Spatial Distribution of Upstream Events: Its Implication for Their Origin will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1439677