Variations in Ion-Component Pressure during Dipolarization in the Near-Earth Magnetotail Plasma Sheet

Abstract

The dynamics of fluxes of thermal and suprathermal H+ and O+ ions and the pressure variations of these components during 11 events of magnetic field dipolarization in the plasma sheet of the geomagnetic tail are analyzed based on Cluster satellite observations. It was found that the energy of H+ and O+ ions corresponding to the maximum flux approached or exceeded the upper energy threshold of CODIF thermal plasma mass spectrometers (~40 keV) in all of the events. During such periods, the determined values of the density, temperature, and pressure in an energy range up to 40 keV are underestimated as compared to the actual values. To determine the pressure during such intervals, we used measurements of the ion-component fluxes in an energy range up to 1.3 MeV based on a joint analysis of observations of CODIF and RAPID energy-mass spectrometers. As a result, it was found that the ion pressure during dipolarization with the high-energy component of the spectrum taken into account can be several times higher than the pressure determined in the range up to 40 keV. Using the superposed epoch analysis, we showed that the error associated with underestimation of the pressure of the H+ and O+ ion components is largest during the dipolarization growth phase. The underestimation is most significant for the O+ ion pressure.