Fluxes of =50-keV protons and =30-keV electrons at ∼35 RE , 1. Velocity anisotropies and plasma flow in the magnetotail

Abstract

The NOAA/APL energetic particle experiment (EPE) on Imp 7 (Explorer 47) is capable of measuring hot plasma flow with a temporal resolution of 20 s if the densities exceed approx.0.1 cm/sup -3/. The lowest-energy electron channel (30--90 keV) can detect plasma with kTapprox.1 keV, while the lowest-energy proton channel (50--200 keV) can detect plasmas at similar temperatures if they have a bulk velocity of approximately-greater-than50 km s/sup -1/. The bulk velocities can be deduced from the measured proton angular distributions (16 sectors in the ecliptic) by using straightforward expressions derived from phase space transformations of a Maxwellian distribution. Representative examples are given for quiet time flow in the magnetosheath (Vapprox.500 km s/sup -1/, kTapprox. =5 keV) and the magnetotail (Vapprox.70 km s/sup -1/, kT/subp/approx.10 keV), with T/subp//T/sube/>3 in both cases. A detailed example of a class of high-intensity events that occur in the plasma sheet in the dusk sector of the magnetosphere is also presented. The 1-hour event (0520--0620 UT, October 3, 1973) was associated with a 1500-..gamma.. depression in the H component of the geomagnetic field at Barrow, Alaska. Tailward velocities of 1260 km s/sup -1/ were deduced during the expansive phase of the substorm, and sunward velocities ofmore » approx.950 km s/sup -1/ during the recovery. Comparison with higher-energy proton measurements on the same spacecraft over the first year of data (September 1972 to October 1973) reveals that the larger events often have a nonthermal tail, although bulk velocities, densities, and temperatures deduced from the smaller events are consistent with previous measurements of plasma flow by other workers. (AIP)« less