IMAGING THE MAGNETOSPHERE WITH ENERGETIC NEUTRAL ATOMS ENA A NEW WINDOW ON SPACE PLASMA

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IMAGING THE MAGNETOSPHERE WITH ENERGETIC NEUTRAL
ATOMS (ENA)-A NEW WINDOW ON SPACE PLASMA

• Pontus C. Brandt, Donald G. Mitchell, Edmond C.
  Roelof
• The Johns Hopkins University Applied Physics
  Laboratory
• NPS Physics Colloquium, Monterey, CA, 23 May 2003

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OUTLINE

• Basic space plasma physics
• What is space plasma?
• The Solar wind
• The Magnetosphere and its regions
• Energization and formation of the magnetosphere
• Space measurements
• In-situ measurements
• UV imaging
• ENA imaging
• Interpreting images linear inversion
• Contributions of space plasma imaging
• The IMAGE mission
• The new picture of the ring current
• Seeing the magneto-ionosphere coupling
• ENA imaging at other planets
• The CASSINI mission to Saturn

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SPACE PLASMA

• A plasma is the fourth state of matter (solid,
  liquid, gas and plasma).
• Plasma is an ionized gas and in space it is
  considered to have an equal number of electrons
  and positive ions (quasi-neutral).
• Plasma is the dominating state of matter
  (99.99999 of the mass in the universe).
• Plasma is governed by electric and magnetic
  forces (very little by gravity).
• A magnetized plasma in motion generates an
  E-field relative to an observer. (EvxB)
• Most space plasmas are collision less (example
  solar wind particles have a mean free path around
  1 AU!)

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THE SOLAR WIND

• Constant stream of protons and electrons.
• Varying intensity (Coronal Mass Ejections).
• Varying magnetic field (IMF).

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SOLAR WIND INTERACTION

• Southward IMF ?
• IMF reconnects with Earths magnetic field.
• With one foot on the surface and one foot in the
  solar wind, the field lines are draped
  anti-sunward (solid lines).
• Plasma is flows around the magnetosphere (dashed
  lines).
• Plasma is carried with field lines in to the
  center tail of the magnetosphere, where it
  reverses direction and is convected sunward again
  (recirculation of field lines).
• There is an E-field associated with the flow
  (chicken and egg problem?).
• Northward IMF?
• The magnetosphere is closed and less plasma
  enters.

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EARTHS MAGNETOSPHERE
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CHARGED PARTICLE MOTION

• Charged particles spiral around magnetic field
  lines.

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CHARGED PARTICLE DRIFT

• Force applied to charged particle in a magnetic
  field will result in drift.

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TRANSPORT IN THE MAGNETOSPHERE

• Electric field force ? ExB drift (Caution
  E-field does NOT cause the flow!)

• Centrifugal force ? curvature drift

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ENERGIZATION IN THE MAGNETOSPHERE(Not fully
understood yet.)

• Conservation of first adiabatic invariant heats
  plasma in the perpendicular direction.
• Sunward ExB flow from tail increases
  perpendicular energy when the plasma encounters
  stronger magnetic field strength.
• The flux tube volume decreases ? energy density
  (pressure) goes up.
• Geomagnetic storms
• Violations of the first adiabatic invariant
  (scattering) lead to net energy increase
• Scattering in collisionless plasmas?? EM waves!
• Sudden magnetic reconfigurations. substorms

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SIMPLE MAGNETOSPHERE
Corotation E-field plasma corotating with
Earths magnetic field creates E-field.
Convection E-field Earthward flow from the tail
sets up cross-tail E-field. Governed by IMF.
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Predictions in a simple magnetosphere

• IMF southward Plasma on open trajectories. The
  main phase of a geomagnetic storm.
• IMF turns north ? convection E-field turns off ?
  only corotation field left ? plasma curv-grad
  drifts in closed trajectories. Recovery phase.
• There should be a region of cold plasma on closed
  equi-potentials that can never escape this
  system.?Plasmasphere

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EARTHS MAGNETOSPHERE
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MEASUREMENTS

• In-situ charged particle spectrometers
• Detailed information on energization processes,
  but very little global context.
• Imaging
• Photon imaging
• Aurora
• Plasmasphere
• ENA imaging The first tool to image proton
  plasma.

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IMAGE Imager for Magnetopause-to-Aurora Global
Exploration
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B. R. Sandel, Univ. of Arizona Lead Investigator
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ENA PRODUCTION
ION FLUX
EXOSPHERE
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ENA Detection Techniques
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The HENA imager
High-Energy Neutral Atom (HENA) Imager
Lead Investigator D. Mitchell, Applied Physics
Lab
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ENA IMAGES NOT ONLY PRETTY PICTURES
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LINEAR INVERSION OF ENA IMAGES

• 1. Transform ENA production integral to linear
  equation system.

Typical ENA image obtained during a storm
mainphase at 1800 UT 4 Oct 2000.
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LINEAR INVERSION OF ENA IMAGES

• 2. Solve the linear system with a constrained
  least squared fit method.

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THE SOLUTION
Above the equator the current connects to the
ionosphere
Electrical current lines close to the equator
close on themselves
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The Bastille Day Magnetic Storm

• Typical storm sequence
• mainphase convection field ON, asymmetric, open
  drift trajectories (ExB drift curv-gradB
  drift).
• recovery convection field OFF, symmetric,
  closed trajectories (curv-gradB drift).
• Dst is a measure of current strengths (NOTE
  probably more related to ionospheric currents
  than the ring current itself!)

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UV Detection Techniques
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Plasmasphere features
24 May 2000
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HENA (39-60 keV) and EUV
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LENA Solar Wind Neutrals Polar Ion Outflow
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LENA Solar Wind Neutrals
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SEEING THE COUPLING

• Pressure ehancement on nightside.
• Region 2 current intensification.
• Evening subauroral ionosphere
• Intense E-fields.
• High (gt1000 m/s) sunward flows.
• Ionospheric uplift (seen by GPS receivers).

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CASSINISATURN ORBIT INSERTION JULY 2004

• ENA imager INCA almost identical to IMAGE/HENA.
• Magnetospheric system is much different from
  Earth.
• Rotation is faster
• Satellites leave gas torii in their trails.

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THE IO TORUSJupiter fly-by
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THE IO TORUS DECONVOLVED
Jupiter ring current plasma
ENA emissions from enhanced neutral gas torus
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ENA IMAGING DISCOVERIES/CONTRIBUTIONS

• EARTH
• The ring current drives some of the dynamics of
  the ionosphere and plasmasphere.
• Mainphase ring current is on the nightside and
  appears to be an inflow-outflow system.
• Substorms appears to energize O ions
  dramatically.
• LENA imaging of the ion outflow from the polar
  caps in response to solar wind pressure.
• LENA imaging of the solar wind interaction with
  the magnetosphere.
• OTHER PLANETS
• Jupiter/Saturn (Cassini/INCA) general plasma
  distribution and interaction with rings, torii,
  satellites.
• Mars/Venus (Mars/Venus Express/Aspera-3/4)
  interaction with solar wind and atmospheric
  escape.
• HELIOSPHERE
• 2.5 yrs of left-over ENAs has put severe
  constraints on the theories for
  interaction/acceleration at the heliospheric
  termination shock.

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THE END.