Three crossings of the lobe‐plasma sheet boundaries encountered within Earth's distant magnetotail with the Geotail spacecraft are analyzed in terms of slow‐mode shocks. Quantitative comparisons with theoretical predictions for a steady state, one‐dimensional shock are made based upon measurements of the three‐dimensional velocity distributions of protons and electrons and of the magnetic fields. The observed plasma moments and magnetic field upstream from the shock are successfully used to predict these parameters in the downstream region. Slow‐mode Mach numbers in the upstream and downstream regions are also shown to be above and below unity, respectively, as required for the slow‐mode shock transition. However, a consideration of the relative uncertainties for the upstream and downstream slow‐mode Mach numbers allows convincing identifications for only two of the boundaries as slow‐mode shocks. Low number densities of plasmas for the other boundary, ∼0.1/cm3, are responsible for the large relative uncertainties for the Mach numbers. This analysis of slow‐mode shocks, together with a comprehensive accounting of statistical uncertainties and variances, allows us to provide firm evidence for the existence of slow‐mode shocks in Earth's distant magnetotail.

[1] It has been reported that Pi2 pulsations can be excited under extremely quiet geomagnetic conditions (K p = 0). However, there have been few comprehensive reports of Pi2 pulsations in such a near ground state magnetosphere. To understand the characteristics of quiet-time Pi2 pulsations, we statistically examined Pi2 events observed on the nightside between 1800 and 0600 local time at the low-latitude Bohyun (BOH, L = 1.35) station in South Korea. We chose year 2008 for analysis because geomagnetic activity was unusually low in that year. A total of 982 Pi2 events were identified when K p Ä 1. About 80% of the Pi2 pulsations had a period between 110 and 300 s, which significantly differs from the conventional Pi2 period from 40 to 150 s. Comparing Pi2 periods and solar wind conditions, we found that Pi2 periods decrease with increasing solar wind speed, consistent with the result of Troitskaya (1967). The observed wave properties are discussed in terms of plasmaspheric resonance, which has been proposed for Pi2 pulsations in the inner magnetosphere. We also found that Pi2 pulsations occur quasi-periodically with a repetition period of 23-38 min. We will discuss what determines such a recurrence time of Pi2 pulsations under quiet geomagnetic conditions.

Plasma plume and thruster performance characteristics associated with multiply charged ions in a cylindrical type Hall thruster (CHT) and an annular type Hall thruster are compared under identical conditions such as channel diameter, channel depth, propellant mass flow rate. A high propellant utilization in a CHT is caused by a high ionization rate, which brings about large multiply charged ions. Ion currents and utilizations are much different due to the presence of multiply charged ions. A high multiply charged ion fraction and a high ionization rate in the CHT result in a higher specific impulse, thrust, and discharge current. V

A lobe‐plasma sheet boundary observed within Earth's distant magnetotail (XGSM ≃ −135 RE) with the Geotail spacecraft is interpreted in terms of a slow‐mode shock. Measurements of the three‐dimensional velocity distributions of protons and electrons and of the magnetic fields allow a quantitative comparison with theoretical predictions for a steady‐state, one‐dimensional shock. The observed plasma moments and magnetic field upstream from the shock are successfully used to predict these parameters in the downstream region. The measured parameters for this example of a lobe‐plasma sheet boundary are in sufficient agreement with the theoretical predictions to provide considerable confidence that this boundary is a slow‐mode shock.

Forty‐three examples of ISEE 1 tailward flank side magnetopause crossings are examined and directly compared with upstream solar wind parameters. The crossings are classified into two groups. In the first group, a few sudden magnetopause crossings are observed, whereas repeated magnetopause crossings and oscillatory motions, often with boundary layer signatures, are observed in the second group. These distinctive characteristics of the two groups are interpreted in terms of the surface waves due to the Kelvin‐Helmholtz instability. It is found that low solar wind speed tends to favor characteristics of the first group, whereas high solar wind speed yields those of the second group. However, no evident correlations between the groups and the interplanetary magnetic field directions are found.