Abstract
Abstract. The penetration of plasma sheet ions into the inner magnetosphere is very important to the inner magnetospheric dynamics since plasma sheet ions are one of the major particle sources of ring current during storm times. However, the direct observations of the inner boundary of the plasma sheet are fairly rare due to the limited number of satellites in near equatorial orbits outside 6.6 RE. In this paper, we used the ion data recorded by TC-1 from 2004 to 2006 to study the distribution of inner boundary of ion plasma sheet (IBIPS) and for the first time show the observational distribution of IBIPS in the equatorial plane. The IBIPS has a dawn-dusk asymmetry, being farthest to the Earth in the 06:00 08:00 LT bin and closest to the Earth in the 18:00–20:00 LT bin. Besides, the IBIPS has also a day-night asymmetry, which may be due to the fact that the ions on the dayside are exposed more time to loss mechanisms on their drift paths. The radial distance of IBIPS decrease generally with the increase of Kp index. The mean radial distance of IBIPS is basically larger than 6.6 RE during quiet times and smaller than 6.6 RE during active times. When the strength of convection electric field increases, the inward shift of IBIPS is most significant on the night side (22:00–02:00 LT). For Kp ≤ 0+, only 16% of IBIPSs penetrate inside the geosynchronous orbit. For 2 ≤ Kp < 3+, however, 70% of IBIPSs penetrate inside the geosynchronous orbit. The IBIPS has weak correlations with the AE and Dst indexes. The average correlation coefficient between Ri and Kp is −0.58 while the correlation coefficient between Ri and AE/Dst is only −0.29/0.17. The correlation coefficients are local time dependent. Particularly, Ri and Kp are highly correlated (r=−0.72) in the night sector, meaning that the radial distance of IBIPS Ri in the night sector has the good response to the Kp index These observations indicate that Kp plays a key role in determining the position of IBIPS.
Highlights
The plasma sheet is the region of closed field lines in the equatorial magnetotail, where the particles are within the region of open electric and magnetic drift paths
In our work, using the ion data of TC-1 of Double Star Program (DSP) in the inner magnetosphere, we study the distribution of inner boundary of ion plasma sheet (IBIPS) in the equatorial plane and its relations with Kp, Dst and AE indexes
In this paper, based on a dataset of 310 crossing events of inner boundary of ion plasma sheet detected by TC-1 from 2004 to 2006, we for the first time show the observational distribution of inner boundary of ion plasma sheet in the equatorial plane
Summary
The plasma sheet is the region of closed field lines in the equatorial magnetotail, where the particles are within the region of open electric and magnetic drift paths. Some important substorm and geomagnetic storm phenomena in the inner magnetosphere such as ring currents and particle injections are closely related to the plasma sheet. The plasma sheet is believed to be one of the major particle source for the ring current population (10–200 keV ions and electrons) (Chen et al, 1994; Jordanova et al, 1998; Kozyra et al, 1998; Wang et al, 2008). The direct observations of the inner boundary of the plasma sheet are fairly rare due to the limited number of satellites in near-equatorial orbits outside 6.6 RE and previous studies have mainly used data from Geosynchronous orbit (Maurice et al, 1998; Korth et al, 1999; Korth and Thomsen, 2001) or the mapped data above equatorial plane (Friedel et al, 2001).
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