Ion Equatorial Distributions from Energetic Neutral Atom Images Obtained From IMAGE during Geomagnet

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Ion Equatorial Distributions from Energetic
Neutral Atom Images Obtained From IMAGE during
Geomagnetic Storms

• Zhang, X. X., J. D. Perez, M.-C. Fok
• D. G. Mitchell, C. J. Pollock and X. Y. Wang

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Outline

• Introduction
• Image Inversion techniques
• Ion equatorial distributions deconvolved from ENA
  images.
• Comparisons b/w deconvolved results and
  Simulation
• T89 and T96 magnetic field model
• Discussion and summary

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Introduction

• What are Energetic Neutral Atoms (ENAs)?
• Where are ENA Sources come from?
• Why are ENAs so important?
• How to get ENA flux?
• How to extract the parent ion information from
  the ENA flux

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What are ENAs?

• Neutral Atoms (ENAs) are generated when single
  charged ions interact with neutral particles via
  charge-exchange collisions.
• Ex
• H H ? H H
• O H ? O H

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Where are ENA Sources ?

• Whenever energetic charged particles interact or
  coexist with neutral sources, ENAs are produced.
• The hemispheric ENA
• Planetary magnetospheres
• Laboratory plasma
• ENAS mainly comes from inner magnetosphere
• or Ring Current region

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Why are ENAs so important?

• Specific Energetic neutrals overcomes planetary
  escaping energy (gt 0.6eV/nucleon)
• ENA s are not affected by E and B fields
• ENAs travel in approximately straight line from
  the charge-exchange sites
• ENAs carry with important information of energy,
  composition, PAD and directions of source ion
  distributions

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How to get ENA flux?

• ENA Imaging ? Optical Imaging
• The emission sites are optically thin
• The neutral background likes a screen
• The ENAs can be imaged to form a 2-D image, not
  3-D image.
• High altitude imaging better than low altitude

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ENA image and deconvolution

• ENA images from MENA HENA fisheye
• Deconvolved ion flux from ENA images
• Ion distributions
• Pitch angle anisotropy

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How to extract ion information from ENA Image

• Forward modeling techniques
• A set of parameters keeps updating
• Theoretical and empirical models
• matching simulated image
• Image inversion techniques
• Base on actual ENA image data
• A set of linear spatial expansion/spline
• smooth and fitting the data by minimizing ?2

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Deconvolution techniques

• Developed and improved by Dr. Perez and also
  applied to simulated data and IMAGE ENA data

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Deconvolution from ENA

• Ion distributions deconvolved from actual ENA
  images by expanding ion flux distribution in term
  of 3-cubic splines.
• Requiring
• fit the data by minimizing ?2 1
• smooth the data using smallest 2nd
  derivatives of ion flux distributions.

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New features

• The response function of instrument (new)
• Charge-exchange with
• Hydrogen geocorona
• Oxygen in the exosphere (new)
• Exobase density derived from MSISE 90
• Solar radio flux parameters,
• (1) F107a ? 3-month average
• (2) F107 ? previous days value
• (3) Ap ? daily average

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Important and needed

• HENA response function obtained from Bob
  Demajistre (APL)
• HENA data extraction code from
• Pontus CSon Brandt (APL)
• MENA data extraction code from
• Joerg-Micha Jahn (SWRI)

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Pitch Angle anisotropy
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Ion equatorial distributions from ENA images.

• Case 1 Ion distributions dependence on Energies
  (Aug. 12, 2000)
• Case 2 Ion distribution drifting(June 10, 2000)
• Case 3 Ring current structures and ion
  distribution patterns
• Case 4 Ion flux decay and intensify

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Ion distributions via Energies

• Ion distributions from MENA and HENA images on
  Aug. 12, 2000 at time 1100UT
• The ion fluxes from MENA and HENA show their
  different source locations,
• pre-midnight for lower energies (MENA)
• post-midnight for higher energies (HENA)
• the flux intensity drops from low energy
  to high energy

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Ion distributions via Energies
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Ion distributions via drift

• Ion distributions from MENA and HENA images on
  June 10, 2000 at different time
• The ion fluxes from MENA and HENA show their
  different azimuthal drifts,
• small drift for lower energy (MENA)
• drift west for higher energy (HENA)
• DriftEgradientcurvatureco-rotation

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Dst, SYM, ASY, AE index
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Small Drift for lower energy
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Big Rotation
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Ion distributions via symmetry

• Ion distributions from MENA and HENA images on
  June 10 and Oct. 4, 2000
• The ion fluxes from MENA and HENA show different
  ring current patterns/ring current structures
• (MENA)
• (HENA)

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Dst, SYM, ASY, AE index
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Symmetric ring current
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Ring Current breakup
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Ion flux decomposition
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Ion flux evolving and decaying

• Ion flux intensity variations from MENA on Aug.
  12, 2000. (solar wind plasma and IMF)
• drops at the end of main phase
• decay rapidly at the initial recovery phase
• Intensify at the time of turning direction of Bz
• Round 1400, substorms contribute and intensify
  the ion fluxes but ENA did not show intense
• Dst, AE, ASY, SYM

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Ion flux decay and intensify
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Solar wind Plasma
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IMF
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Dst, SYM, ASY, AE index
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Deconvolutions via Simulations

• What are physics in them? Substorm/electric field
  convection
• Most large scale structures exist in both
  Deconvolutions and simulations
• There also have some differences.

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Deconvolution and Simulation
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Discussion and summary

• Equatorial ion flux and PAD distributions can be
  extracted from ENA images.
• Deconvolutions show agreements with Foks ring
  current model for most large scale structures.
  Substorm injections intensify the ion fluxes and
  ENA flux.
• Different energies, phase, and IMF show different
  ion flux distributions and PADs
• The ion fluxes show symmetric and asymmetric ring
  structures