Quiet-time Pc 5 pulsations in the Earth's magnetotail: IMP-8, ISEE-1 and ISEE-3 simultaneous observations

Quasi-periodic Pc 5 pulsations have been\udreported inside and just outside the Earth's magnetotail during intervals of low\udgeomagnetic activity. In order to further define their characteristics and\udspatial extent, we present three case studies of simultaneous magnetic field and\udplasma observations by IMP-8, ISEE-1 (and ISEE-2 in one case) in the Earth's\udmagnetotail and ISEE-3 far upstream of the bow shock, during intervals in which\udthe spacecraft were widely separated. In the first case study, similar\udpulsations are observed by IMP-8 at the dawn flank of the plasma sheet and by\udISEE-1 near the plasma sheet boundary layer (PSBL) near midnight local time. In\udthe second case study, simultaneous pulsations are observed by IMP-8 in the dusk\udmagnetosheath and by ISEE-1 and 2 in the dawn plasma sheet. In the third case\udstudy, simultaneous pulsations are observed in the north plasma sheet boundary\udlayer and the south plasma sheet. We conclude that the pulsations occur\udsimultaneously throughout much of the nightside magnetosphere and the\udsurrounding magnetosheath, i.e. that they have a global character. Some\udadditional findings are the following: (a) the observed pulsations are mixed\udmode compressional and transverse, where the compressional character is more\udapparent in the close vicinity of the plane Z_GSM=0; (b) the\udcompressional pulsations of the magnetic field in the dusk magnetosheath show\udpeaks that coincide (almost one-to-one) with similar peaks observed inside the\uddawn plasma sheet; (c) in the second case study the polarization sense of the\udmagnetic field and the recurrent left-hand plasma vortices observed in the dawn\udplasma sheet are consistent with anti-sunward moving waves on the magneto-pause;\ud(d) pulsation amplitudes are weaker in the PSBL(or lobe) as compared with those\udin the magneto-tail's flanks, suggesting a decay with distance from the\udmagnetopause; (e) the thickness of the plasma sheet (under extremely quiet\udconditions) is estimated to be ~22 R_E at an average location\udof (X, Y)_GSM=(16, 17) R_E, whereas at\udmidnight local time the thickness is ~14 R_E. The detected\udpulsations are probably due to the pressure variations (recorded by ISEE-3) in\udthe solar wind, and/or the Kelvin Helmholtz instability in the low-latitude\udboundary layer or the magnetopause due to a strongly northward IMF