Measurements of plasma in the magnetospheric tail lobes

• Published in: Advances in space research 1996, Vol.18 (8), p.63-67
• Main Authors: Vaisberg, O.L, Avanov, L.A, Burch, J.L, Waite, J.H
• Format: Article
• Language: English
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/0273-1177(95)00998-1

The plasma spectrometer SKS on the Prognoz 8 satellite was able to measure the very dilute plasma in the tail lobe at distances 15 – 20 Earth radii about 50% of the time. The energy of the ions, being in the range of several hundred electron volts, decreases as the satellite moves from the high-latitude magnetopause to the plasma sheet. The velocity spread of the ions is narrow in the direction of motion, corresponding to a temperature of several eV. The temperature in the transverse direction is 2 to 3 times higher. Comparison with magnetospheric convection models suggests that these ions originate at low altitudes in the region near the cusp and are separated in the magnetospheric velocity spectrometer. Observed velocity variations along the spacecraft trajectory suggest the existence of a characteristic velocity profile and a characteristic temporal/spatial scale. Comparison of simultaneous E q measurements with mass-selective detector measurements of protons and alpha particles suggests that lobe plasma at these distances consists primarily of oxygen ions. The average ion flux density is about 3×10 5 cm −2 s −1, giving estimated total flux over the lobe about 10 25 s −1, comparable to cusp/cleft source.