GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE

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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE
Particle energy in the magnetosphere is carried
mainly by trapped protons. Proton auroras are
caused by protons which leave the magnetosphere
and precipitate into the atmosphere. IMAGE, is
the first satellite to make remote sensing
measurements of proton and electron auroras
separately. Observations of proton auroras can
pin-point the onset location of the substorm.
SI-12 (Protons) SI-13 (mainly electrons)
Combined image
Mende et al., Global observations of proton and
electron auroras in a substorm. Geophys. Res.
Lett., submitted 2000. Frey et al., The electron
and proton aurora as seen by IMAGE-FUV and FAST.
Geophys. Res. Lett., submitted 2000.
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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE
MEASUREMENTS IMAGE carries an array of imagers
to take pictures of the magnetosphere and the
aurora.
There are three Far Ultraviolet (FUV) auroral
imagers which observe the aurora simultaneously
in three wavelength channels . 1. Wideband
Imaging Camera (WIC) observes nitrogen emissions
excited by auroral electrons and protons. 2.
Spectrographic Imager SI12 channel observes
auroral Lyman alpha produced by protons. 3.
Spectrographic Imager SI13 channel observes
oxygen emission excited by auroral electrons and
protons.
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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE
WIC
SI-12
In order to validate the IMAGE FUV observations
we have performed coordinated observationss
with FAST auroral satellite, which measured the
precipitating particles by in situ particle
counters. FAST orbit is illustrated in red.

SI-13
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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE
WIC intensity (red) along FAST track shows good
agreement with particle (proton and electron)
energy flux measurements by FAST.
SI-12 intensity (red) along FAST track shows good
agreement with proton flux measurements by FAST.
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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE
Auroral dynamics can be best understood in terms
of its substorm cyclic behavior. Substorms are
spontaneous intensifications of the aurora
accompanied by poleward expansion of the auroral
oval. Prior to IMAGE our picture of the global
auroral substorm morphology was based only on
electron aurora observations even though we knew
that protons play a significant role in the
substorm process. IMAGE FUV has observed several
substorms in proton and electron auroras.
Significant images of a small substorm are
presented in the following slide.
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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE
FUV images of a small substorm
midnight
WIC
SI-12
1956
2004
2015
2023
2031
2047
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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE
1956 Pre-substorm situation faint single arcs
are co-located in WIC and SI-12. 2004 Sudden
brightening in the electron aurora (WIC) near
mid-night at about the same latitude as the
proton aurora showing that the onset occurs in a
region where there is significant proton
precipitation. 2015 Brightening (WIC) propagates
towards dawn (to the left) and poleward with
proton aurora (SI-12) expanding poleward. 2023
Brighter surge in (WIC) is considerably more
poleward than the bulk of the protons which reach
peak brightness at this time. 2031 Bright
poleward arc (WIC) while protons fade at high
latitude 2047 Post substorm protons re-formed at
low latitudes while the electron aurora has
propagated poleward and dawnward..
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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE
Conclusion Substorm onset occurs in the region
of closed field lines containing protons. This
observation supports substorm models which claim
that substorms begin near the earth.