Statistical survey of magnetic and velocity fluctuations in the near‐Earth plasma sheet: International Sun Earth Explorer (ISEE‐2) measurements

Abstract

International Sun‐Earth Explorer (ISEE‐2) satellite observations of low‐frequency magnetic field and ion velocity fluctuations in the Earth's magnetotail are compared with corresponding observations from the Active Magnetospheric Particle Tracer Explorers/Ion Release Module (AMPTE/IRM). Solar activity during these two missions is different and thus also considered. The ISEE‐2 analysis is performed on the data taken from satellite passes through the Earth's plasma sheet in 1978 and 1979 near solar maximum. The data is divided into 2298 ten‐minute‐long intervals where the averages of the magnetic field, ion velocity, and plasma parameter's amplitudes are statistically calculated for each interval. We find no significant dependence of the amplitude of the ion velocity and magnetic field fluctuations on the magnetotail distance or on the distance from the neutral sheet. The correlation coefficient between the geomagnetic activity and the amplitude of both ion velocity and magnetic field fluctuations in the ISEE‐2 measurements is smaller than the one found for the AMPTE/IRM passes through the plasma sheet. When comparing the two satellite data sets for the same plasma sheet region, we obtain a significantly higher upper bound for the ISEE‐2 fluctuating magnetic field energy density. Our results suggest that the significantly increased magnetic field fluctuation amplitude in the plasma sheet during the ISEE‐2 satellite passes is due to the increased solar activity near solar maximum.