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Cluster observations of hot He + events in the inner magnetosphere
Author(s) -
Yamauchi M.,
Dandouras I.,
Rème H.,
Nilsson H.
Publication year - 2014
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2013ja019724
Subject(s) - physics , magnetosphere , substorm , plasmasphere , plasma sheet , earth's magnetic field , local time , astrophysics , latitude , cluster (spacecraft) , astronomy , magnetic field , plasma , nuclear physics , statistics , mathematics , quantum mechanics , computer science , programming language
In the inner magnetosphere inside 65° invariant latitude, Cluster Ion Spectrometry detected hot He + events of about a few tens to several hundred eV without the same types of hot H + signature at the same energy. During the 2001–2006 period when the Cluster orbit was almost constant and approximately north‐south symmetric at constant local time near the perigee, we found nearly 20 examples in Cluster spacecraft 4. These hot He + events are morphologically classified into two burst types and two dispersed types: (1) Short intensification of He + (1a) without corresponding H + or O + signatures, or (1b) with H + signature at different pitch angles. (2) Energy‐latitude dispersed He + stripes that continues for tens of minutes at hundreds to a few thousand eV range (2a) at different drift shell from energy‐latitude dispersed H + stripes, or (2b) with very weak H + signature if the energy is constant. While type‐1a is observed during or right after substorm activities, type‐2b is found after long quiet periods, i.e., after long drift. The relationship with the geomagnetic activity indicates that the plasmasphere can be energized in a mass‐dependent way in the evening sector during substorms to form the bursty types (type‐1), while the selective He + energization can also take place during quiet periods near the noon. On the other hand, the source of the two dispersed types (type‐2) must be remote from the observation point, and the location and the geomagnetic conditions at the time of the He + filtering is an open question.