T. E. Eastman

High charge state carbon and oxygen ions in Earth's equatorial quasi‐trapping region

Observations of energetic (1.5 - 300 keV/e) medium-to-high charge state (+3 ≤ Q ≤ +7) solar wind origin C and O ions made in the quasi-trapping region (QTR) of Earths magnetosphere are compared to ion trajectories calculated in model equatorial magnetospheric magnetic and electric fields. These comparisons indicate that solar wind ions entering the QTR on the nightside as an energetic component of the plasma sheet exit the region on the dayside, experiencing little or no charge exchange on the way. Measurements made by the CHarge Energy Mass (CHEM) ion spectrometer on board the AMPTE/CCE spacecraft at 7 7, that is, solar wind secondaries are produced at L < 7, and (2) solar wind secondaries do not form a significant portion of the plasma sheet population injected into the QTR. We conclude that little of the energetic solar wind secondary ion population is recirculated through the magnetosphere.

Magnetospheric plasma regimes identified using Geotail measurements: 2. Statistics, spatial distribution, and geomagnetic dependence

We investigate the spatial distribution, solar-terrestrial correlation, and basic statistics of a long sequence of plasma regime identifications through the probability of observation P at downtail distances of ∼30 60 RE and remains high tailward; and (f) At xagsm 100 RE): (a) Conditions appear more chaotic. PS, BL, or MS can be observed anywhere inside the nominal magnetotail domain; (b) Compared to the middle magnetotail, PS and BL are observed more dawnward of the XAGSM axis and P(PS) is significantly lower (most distinctly at Kp > 3o); (c) P(PS) is centered dawnward of the XAGSM axis for both low and high Kp; and (d) At xagsm ≥ 170 RE, P(BL) is greater than P(PS) or P(MS), with P(MS) ≈ P(PS). P(LB) > 0, but low, out to xagsm ≥ 200 RE. In general, the downtail distributions of the magnetospheric plasma regimes depend more strongly on xagsm than on Kp, however the YAGSM distribution of P(PS) depends strongly with both xagsm and Kp. Magnetotail width varies weakly with xagsm and Kp.

Ion composition and charge state of energetic particles in flux ropes/plasmoids

Measurements from the energetic particles and ion composition (EPIC) instrument on Geotail are used to investigate the relative abundance of different ion species at energies ∼10 keV to 3 MeV in flux ropes or plasmoids detected at various downstream distances from ∼23 RE to ∼190 RE in the tail. In terms of charge state, we find that during encounters with these structures most of the oxygen ions are singly charged, i.e., O+ ions of ionospheric origin, while most of the helium ions are doubly charged, i.e., He++ ions of solar wind origin. Therefore the ion species from the solar wind and the ionosphere appear to be thoroughly mixed inside flux ropes or plasmoids, just like the ion composition in the tail outside these structures. This study also reveals a variety of changes in the abundance of ionospheric oxygen ions within flux ropes or plasmoids. These range from simultaneous enhancements of ionospheric oxygen ions within the structure to delayed enhancements or no significant change of ionospheric oxygen ions throughout the entire structure. The amount of ionospheric oxygen ions present in flux ropes or plasmoids increases with higher geomagnetic activity as gauged by the Kp index, but it shows no apparent trend with the downstream distance. The lack of consistent enhancement of ionospheric oxygen ions inside these structures suggests that oxygen ions may not play a significant role in their formation.