SM41A-4235:
Cluster Observations of Energetic O+ Ions Correlated with Ulf Waves in the Night-Side High-Latitude Magnetosheath during a Storm Initial Phase

Thursday, 18 December 2014
Suping Duan1, Chi Wang1, Zhenxing Liu1, Anthony Lui2, Zhaohai He1, Yongcun Zhang1, Henri Reme3 and Iannis Dandouras3, (1)Center for Space Science and Applied Research (CSSAR), CAS, Beijing, China, (2)Applied Physics Laboratory Johns Hopkins, Laurel, MD, United States, (3)IRAP, Toulouse, France
Abstract:
Measurements from Cluster spacecraft C4 are used to investigate the energization of singly charged oxygen ions, O+, by Ultra-Low Frequency (ULF) waves in the night-side high-latitude magnetosheath during the initial phase of an intense storm on 24 October 2011. The number density of O+ ions was ~0.1 cm-3 detected by Cluster C4 within the night-side high-latitude magnetosheath. The observed energetic O+ ion flux was periodic in the ULF wave Pc 5 range, ~ 3 min. The fluctuations of O+ number density, dNO+ were closely correlated with the pulsations of magnetic field, dBx. The phase difference between the dNO+ and dBx is ~ 1800 or ~ 900, which corresponding to the O+ pitch angle distribution mainly in the direction parallel or perpendicular to the magnetic field, respectively. These results indicate that the O+ ions can be energized by Pc 5 waves both in the parallel and perpendicular to the magnetic field in the night-side high-latitude magnetosheath during the storm initial phase. Our observation investigation presents a new source of the abundant energetic O+ in the plasma sheet during the storm main phase, which is from the night-side high-latitude magnetosheath throughout the magnetopause/mantle/lobe region. These energetic ions are likely one of the major sources of O+ filling into the near-Earth plasma sheet and ring current during the storm main phase.