GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE

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Space Science Program October 2000

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.

GLOBAL OBSERVATION OF PROTON AURORAS BY 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.

SI-12 (Protons) SI-13 (mainly electrons) Combined image

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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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WIC SI-12

SI-13

In order to validate the IMAGE FUV observations we have performed coordinated observationss withFAST auroral satellite, which measured the precipitating particles by in situ particle counters. FAST orbit is illustrated in red.

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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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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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19:56 20:04 20:15

20:23 20:31 20:47

FUV images of a small substorm WIC SI-12

midnight

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19:56 Pre-substorm situation: faint single arcs are co-located in WIC and SI-12.20:04 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.20:15 Brightening (WIC) propagates towards dawn (to the left) and poleward with proton aurora (SI-12) expanding poleward.20:23 Brighter surge in (WIC) is considerably more poleward than the bulk of the protons which reach peak brightness at this time.20:31 Bright poleward arc (WIC) while protons fade at high latitude20:47 Post substorm protons re-formed at low latitudes while the electron aurora has propagated poleward and dawnward..

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Conclusion: Substorm onset occurs in the region of closed field lines containingprotons. This observation supports substorm models which claim that substorms begin near the earth.

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GLOBAL OBSERVATION OF PROTON AURORAS BY IMAGE