Fluxes of ≥50-keV protons and ≥30-keV electrons at ∼35RE, 2. Morphology and flow patterns in the magnetotail

Abstract

This paper presents the following six main results from statistical analyses of the morphology of 50- to 200-keV protons and 30- to 90-keV electrons in the magnetotail and magnetosheath using approximately 1 year of data from the NOAA/APL energetic particle experiment (EPE) aboard the Imp 7 satellite at ∼35 RE with an orbital inclination of ∼30° to the ecliptic plane. (1) The 50- to 200-keV proton and 30- to 90-keV electron events in the magnetotail occur primarily in the plasma sheet region. The frequency of proton events in the magnetosheath is comparable to that found in the plasma sheet. However, the frequency of the electron events is considerably smaller in the magnetosheath than in the plasma sheet. (2) The protons show a dawn-dusk asymmetry in the probability of occurrence of the events, while the electrons show little evidence of an asymmetry. (3) The correlation of the electron and proton events in the magnetotail was highest in the dawn sector. (4) The electron event probabilities show a clear correlation with Kp index in both the dawn and the dusk sectors of the magnetotail, although the correlation of proton events with Kp is found only in the dawn sector. (5) The protons show characteristic flow patterns: in the magnetosheath the flow is consistently tailward; in the dusk plasma sheet the proton flow is predominantly sunward, while in the dawn magnetotail the flow pattern is not well defined. The flux associated with the sunward flow in the dusk sector is estimated to be ∼8 × 1025 protons s−1 and is sufficiently large to be a significant source term in magnetospheric dynamics. (6) Very high intensity, highly anisotropic proton events with antisunward flow were measured in the plasma sheet near the dusk magnetopause. During the 1-year interval used in this study a total of 16 events were observed. All occurred in the dusk sector of the magnetotail within a region defined by the lines ZSM = ±5 RE and YSM = 4–22 RE. In all cases the events were followed by an extended period (∼8 hours) in which the protons flow sunward (<100 km s−1) with thermal energy in the range of 6–12 keV.