Conjunction Observations of Energetic Oxygen Ions O⁺ Accumulated in the Sequential Flux Ropes in the High-Altitude Cusp

Abstract

Conjunction observations of the magnetic field and plasma by Cluster and TC-1 at the dayside magnetosphere are presented to investigate the sequential flux ropes transferred from the low latitude boundary layer to the high-altitude cusp on 10 March 2004.Three sequential flux ropes originating from the dayside low latitude magnetopause are first detected by TC-1. After 5.3 min, three sequential flux ropes accumulated with energetic oxygen ions are also detected by Cluster in the high-altitude cusp. The recurrence period of these flux ropes is 3 min. The number density of energetic oxygen ions in the cusp flux rope is 0.25 cm^-3 detected from CIS/CODF instrument on Cluster. It is found that oxygen ions with energy lager than 10 keV have a narrow pitch angle (less than 90°) distribution in the southern high-altitude cusp. While oxygen ions with energy less than 10 keV are distributed in a wide pitch angle from 0 to 180°. Counter-streaming energetic oxygen ions are found in these flux ropes in the high-altitude cusp.This result suggests that the oxygen ions with energy less than 10 keV in the high-altitude cusp have two source regions. One is from the dayside magnetopause, and the other is from the low-altitude cusp. Our investigations first provide evidence that flux ropes at dayside low-latitude magnetopause can carry energetic oxygen ions into the high-altitude cusp region.