Extracted from talks by Janet Kozyra, Don Carpenter, Dennis Gallagher, Bob Clauer, Mike Liemohn, Sta

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SummaryGlobal Models and Data Focus on Inner
Magnetosphere

• Extracted from talks by Janet Kozyra, Don
  Carpenter, Dennis Gallagher, Bob Clauer, Mike
  Liemohn, Stanislav Sazykin, Bill Burke, Stefano
  Orsini, and Pontus Brandt

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Ring Current Issues

• Kinetic RC models consistently reproduce the
  general behavior of the Dst index using
  semi-empirical electric field models and observed
  near-Earth plasma sheet source populations. In
  most cases, overpredict the contribution to Dst
  due to total RC energy as a result of
  uncertainties in the electric field model and/or
  uncertainties in the contribution of
  field-aligned and closure currents to Dst. Do
  not yet include RC self-field. Other non-ring
  current contributions to Dst must be secondary.
• New Predictions
• Main early recovery phase RC is asymmetric and
  dominantly a partial RC loop. Ions move on open
  drift paths to the magnetopause making only one
  pass through the inner magnetosphere. Dominant
  loss is through flow-out on the dayside.
• RC characteristics are rapidly influenced by
  changes in the inner plasma sheet populations and
  in the convection electric field strength
  directly transmitted along open drift paths.
  Following consequences

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• Rapid (as low as 1 hour) loss time-scales during
  main phase due to flow-out which are correlated
  with VBs in the solar wind (related to
  magnetospheric convection strength)
• Two-phase decay -- transition from fast
  flow-out loss to slower charge-exchange loss
  as open drift paths are converted to closed ones
  in the early recovery phase
• Composition changes in the RC driven by
  composition changes in the inner plasma sheet in
  response to changing magnetic activity. Produce
  close correlation between Dst and composition
  changes in the ring current.
• Preconditioning Pre-existing RC populations
  from previous activity are largely swept out of
  the magnetosphere by new activity.
  Preconditioning by prior activity may enter
  through driving of the plasma sheet (RC source
  population) characteristics
• Direct Injection Source? CRRES sees evidence for
  upflowing ions directly injected into the ring
  current region. Not understood how this
  contributes to the ring current formation? Need
  much more information on global distribution,
  persistence, composition, pitch angle and energy
  characteristics of these events. Can global ENA
  images contribute to this issue?

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Ring Current Issues

• Rapid variations in the near-Earth plasma sheet
  density means that low-density flux tubes will be
  convected into the inner magnetosphere behind
  very high density flux tubes. This creates a
  situation in MHD that is unstable to the
  interchange instability. Preliminary RCM results
  indicate that this configuration is only
  borderline unstable. It is stabilized to this
  point either by differential particle drifts or
  numerical diffusion in the model. Further
  investigation is needed. (Sazykin)

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Interpretation of Indices (Focus here on Dst)

• Many signatures contribute to Dst
• MLT-UT maps constructed with 20 ground
  magnetometers show MLT-dependence of signatures
  in addition to global-averaged information
  contained in Dst index
• Show evidence of contributions of current systems
  responding to solar wind pressure hits -- not
  what one would expect from Chapman-Ferraro
  current system -- not removed by standard
  pressure corrections
• Observations indicate that immediate and dramatic
  enhancements in global DP2 current system in
  response to pressure hits overwhelms other
  contributions for several hours after pressure
  hit
• Large-scale substorms produce clear substorm
  current wedges at mid-latitudes. Also associated
  with near in time ring current enhancements. How
  do these signatures impact Dst? Clearly show
  asymmetry of ring current enhancements
• MLT-resolved information will refine our
  understanding of the meaning of the Dst index
• Important for real-time prediction and monitoring
  -- model verificaton -- data ingestion, etc.

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Coupling Processes
Penetration electric fields

• The fundamental importance of the penetration
  electric field for the dynamical behavior of the
  ring current, thermal plasma and global
  ionosphere is becoming increasingly apparent.
  Its role in geoeffectiveness is not completely
  understood.
• Self-consistent magnetic field has important
  consequences. Penetration fields persist for
  longer periods because stretched field
  configuration inhibits the re-establishment of
  shielding by the ring current. Not previously
  appreciated. (Sazykin)
• New information (observations and models)
  indicates that the ring current is highly
  asymmetric and on dominantly on open drift paths
  during the main and recovery phase. This implies
  a strong partial ring current loop with currents
  closing through the ionosphere. Important to
  understand the details of the current closure.
  New effort underway to combine AMIE specification
  of conductivities with FACs from ring current
  model to get realistic current closures

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Coupling Processes
Penetration electric fields

• This current closure (in combination with
  ionospheric conductivity gradients) results in
  strong and persistent penetration electric
  fields. DMSP observed up to 60 kV penetration
  potentials extending equatorward of the auroral
  electron boundary
• Large portion of the penetration potential
  concentrated in small-scale structures called
  SAID events which create high-speed flow channels
  in the ionosphere. Roughly a degree MLAT wide
  and a couple hours in MLT
• Influence of penetration fields can extend all
  the way to the equatorial ionosphere on short
  time scales
• Has global consequences to ionospheric stability
  -- triggers growth of equatorial bubles, related
  also to deep depletions ofequatorial F-region,
  etc.
• Overshielding can develop near the inner edge of
  the ring current (seen on CRRES) -- effects on
  ionospheric potential have been observed on DMSP
• Changes in the global electric field potential
  pattern due to closure of the partial ring
  current through the ionosphere resemble
  statistically modified patterns demonstrated to
  create shoulders in the plasmaspheric
  distribution

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Plasmasphere Issues

• Reasons for variability in the plasmaspheric
  density structure are still not understood.
  Structuring is observed on all scale sizes down
  to L values as low as L2
• Large and highly structured electric fields are
  also observed throughout these regions and are
  correlated with the presence of ring current
  ions. Role of these fields in the structuring is
  not understood.
• Losses of plasmaspheric plasma to the underlying
  regions appear to occur and are also not
  understood.
• What is the dynamical behavior that forms density
  bite-outs (voids)? How are they formed and why
  do they persist (some for up to 40 hours).
• Features already being observed in global images
  are corotating plasmaspheric shoulder, voids
  (density bite-outs). Have not seen detached
  plasma regions yet.
• How do induction fields from substorms modify
  this picture

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What new data shows how it can be used to
explore new issues -- Ring Current

• Can finer-scale structures (in the ring current?
  in the plasmasphere?) indeed be resolved by
  global images? Are other methods needed to
  observe and characterize smaller-scale structures
  and their dynamical behavior
• New statistical ring current models based upon
  AMPTE and CRRES show strong trapped component in
  the period preceeding an event. This component
  disappears during main phase and is replaced by
  population on open drift paths. In recovery,
  phase trapped component again dominates -- in
  agreement with model predictions
• New global observations with HENA show evidence
  of dayside outflow of ring current ions. After
  northward turning of IMF, dayside population of
  ring current is re-established. -- outflow
  predicted by global ring current model for this
  event.
• Caution Pitch angle characteristics can
  dramatically impact which populations show up
  strongly in ENA images. Highly trapped
  distributions show weaker signatures because
  remain in regions of low neutral density.
  Mirroring particles produce strong ENA
  signatures.

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What new data shows how it can be used to
explore new issues -- Ring Current

• Time sequences of global images powerful tool for
  examing new dynamical issues
• conversion of asymmetric to symmetric ring
  current configurations -- conversion of open to
  closed drift trajectories -- how this relates to
  phases of the storm
• nature of flows of ring current ions to the
  dayside magnetopause and contribution to loss
  during the main phase
• composition changes sweeping through the ring
  current region from the nightside plasma sheet as
  magnetic activity varies
• interplay between substorm modification of the
  near-earth plasma sheet populations and enhanced
  convection in ring current build-up
• To make progress on open issues need from global
  observations
• information on the global electric field pattern
  and its evolution during events
• MLT-resolved composition, energy and density of
  the near-Earth plasma sheet (ring current source
  population) and its variation during magnetic
  activity

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What new data shows how it can be used to
explore new issues -- Ring Current

• Information on global distribution of ionospheric
  populations directly injection into the ring
  current region
• Evolution of global plasmaspheric configuration
  including small-scale density structures (to
  specify environment for plasma waves, Coulomb
  losses, etc.)
• Contributions of Global Models
• Enable interpretation of physical processes
  driving the observed global dynamics
• Supply initial guess to support
• ENA inversion (especially related to small-scale
  structures)
• Estimation of global electric field evolution
  from global images

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What new data shows how it can be used to
explore new issues Plasmasphere

• Much can be added to the observational picture
  and many questions answered by global images
  which show the longitudinal extent of
  plasmaspheric structures, their dynamic behavior
  and their relationship to other elements (like
  the ring current, global electric field pattern,
  etc.).
• New features and their dynamical behavior being
  identified in the global images already.
• shoulder in plasmaspheric boundary that
  corotates following formation. Preliminary
  results indicate it may be related to a transient
  feature in the global electric field pattern
  (resembling that produced by the ring current
  penetration electric field)
• Evidence for finger-type structures, voids is
  density
• Clear that need to understand more about
• plasmasphere-ring current interactions
• plasmasphere - superthermal electron interactions
• consequences for ionospheric sources and losses

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What new data shows how it can be used to
explore new issues Global Electric Fields
GLOBAL ELECTRIC FIELD (including PENETRATION
FIELD)

• RCM contributed much to our understanding of
  penetration electric fields -- recently validated
  extensively by comparing DMSP potentials and
  CRRES observations against the model results in
  the magnetosphere and underlying ionosphere for
  the June 1991 storm interval -- uses statistical
  patterns of conductivity and for RC source
  populations -- need to test understanding
  against observations that are more represenatitve
  of selected events
• Preliminary investigations using AMIE
  specifications of the conductivity and calculated
  field-aligned currents from a data-driven ring
  current model show interesting features
• In particular, can these models reproduce the
  small-scale and intense features (SAIDs) that are
  superposed on the larger-scale and weaker
  penetration electric fields

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What new data shows how it can be used to
explore new issues Global Electric Fields

• How do these more complex global convection
  patterns impact the location in MLT and extent of
  open drift paths from the magnetotail that supply
  the ring current source population during storms.
  There are MLT-dependent populations observed at
  geosynchronous orbit with differing energy,
  composition and density characteristics which may
  have interesting impacts on the ring current
  formation
• Can global imaging sequences of plasmasphere
  and/or ring current provide information on the
  penetration fields from their impact on the
  global configuration of the plasmasphere and ring
  current?
• ENA images through determination of the average
  energy of the ring current versus local time may
  be able to provide an estimate of the potential
  drop in the cross-tail field. Work continues on
  this.