Ring Current and Plasmasphere Accomplishments During the GEM IM/S Campaign

1
Ring Current and Plasmasphere Accomplishments
During the GEM IM/S Campaign

• Mike Liemohn
• GEM Workshop Tutorial
• June 27, 2006

2
IM/S Campaign Outcomes and Questions

• How well do we understand the physics of the
  inner magnetosphere?
• What are the physical questions remaining to
  understand the inner magnetosphere?
• How far have we come since the beginning of the
  IM/S Campaign (1998)?
• What advances in observations are needed next?
• Of these, which can be anticipated in current
  plans?
• Which observations can be readily achieved, which
  are dependent on advances in experimental
  physics, and which cannot be currently foreseen
  as possible?
• What advances in modeling are needed next?
• Are there important physical processes that are
  not yet included?
• Can regional models be advanced independent of
  system-wide modeling?
• What advances in numerical technique and
  processing power are needed?

3
Basic Definition Plasmasphere

• Cold Less than 1 eV, maybe up to 10 eV
• Dense 100s-1000s cm-3, lower out near geos.
• Ionospheric source is the subauroral ionosphere
• Mostly Protons oft-quoted composition, 77 H,
  20 He, and 3 O
• E-field dominated spatial extent governed by
  magnetospheric electric field time history
• Important dominates the mass density of the
  inner magnetosphere

4
Basic Definition Ring Current

• Hot 1-400 keV
• Tenuous quiet, 1 cm-3 active, 10s cm-3
• Plasma sheet source is near-Earth magnetotail,
  wherever that comes from
• Mostly Protons During big storms, O can
  dominate
• Complicated Drift E-field, B-field,
  Gradient-curvature terms
• Important Dominates the energy density of the
  inner magnetosphere

5
Ring Current Advances

• Storm-Time Ring Current Morphology
• Partial ring current dominance during storms
• Connection/Feedback with Electric Field
• The ionosphere matters
• Connection/Feedback with Magnetic Field
• The B-field really is tweaked by currents
• Connection/Feedback with Plasma Sheet
• Has anyone seen my source term?
• Connection/Feedback with Plasma Waves
• Collisionless energy transfer

6
Ring Current Morphology

• The ring current is not a ring during storms

Liemohn et al., JGR, 2001
From Don Mitchell
7
Ring Current-FAC-F Relationship

• A pressure peak requires FACs at each end to
  close the partial ring current, and the resulting
  potentials act to expel the pressure peak

Liemohn and Brandt,AGU Mon v. 159, 2005
8
Electric Field Connection

• Partial ring current causes a potential well near
  midnight, changing the hot ion drift paths in the
  inner magnetosphere

Fok et al., SSR, 2003
9
Electric Field, Part 2 SAPS and Flow Channels

• SAPS subauroral polarization stream
• Enhanced outward E-field in dusk/evening sector
  causing faster-than-normal sunward flow
• Flow channels narrow regions of injection
• Enhanced westward E-field in localized sector of
  nightside causing fast injection

Foster and Vo, JGR, 2002
Chen et al., JGR, 2003
10
Magnetic Field Connection
Particle Tracing Model With Inductive-E Pulses

• One-way connection B-field influences on the
  ring current
• Trends in the ring current energy content time
  series are best reproduced when B is stretched
  realistically and when convective inductive
  E-fields are included

Ganushkina et al., JGR, 2006
11
Magnetic Fields 2-Way Coupling

• B-field found from RC result, then fed back to RC
  model
• Pressure (P?) overall significantly smaller
  (half) in self-consistent (SC) case vs. dipole
  field P (not shown) not as affected
• Less plasma delivered close to Earth, but more
  structure
• Less filled flux tubes are able to drift closer
  to Earth

Zaharia et al., JGR, 2005
12
The Flip Side of FeebackEffect of the Hot Ions
on B

• X-Y plane pressures with 3-d B lines for a given
  latitude overdrawn
• Tail stretching
• Pressure much higher near the Earth with kinetic
  code embedded
• Hot ions near Earth alter the field and plasma in
  other areas

With Kinetic Code
Without Kinetic Code
From Toth, Ridley, and De Zeeuw
13
Plasma Sheet Connection

• Plasma sheet density controls the strength of the
  ring current
• Plasma sheet temperature also affects ring
  current intensity

Ebihara Ejiri, JGR, 2000
Liemohn and Ridley, JGR 2002
14
Plasma Wave Connection

• Calculating the EMIC wave energy density
  self-consistently with the hot ions allows for
  nonlinear feedback between them
• Scattering of ions depends on Bw and q
• Preference for field-aligned q
• Also a heat source for the thermal plasma

Khazanov et al., JGR, 2006
15
What is Needed for Improvement

• Major Modeling Needs
• More fully develop self-consistency in the models
• Continue to couple ring current models to other
  inner magnetospheric models and to global models
• Better electron ring current loss
  lifetimes/diffusion coefficients
• Algorithms for accurate hot plasma precipitation
  calculation
• Major Observational Needs
• Routine ion composition measurements at GEO
• More reliable electron ring current measurements
• Multi-spacecraft particle, field, and wave
  measurements in the ring current region
• More/better ionospheric conductance measurements

16
Plasmasphere Advances

• Global Morphology
• The plasmapause is lumpy, and we know why
• Magnetic Field Effects
• The plasmasphere is more than just an E-field
  history integrator
• Plasmaspheric Refilling
• Diffusive equilibrium is not quite right
• Mass Density
• ULF wave analysis comes of age

17
Global Morphology

• IMAGE EUV has shown the plasmasphere to be a
  lumpy and bumpy creature
• Tracer of the time-history of inner mag. fields
  (mostly E, also B)

Sandel et al., SSR, 2003
18
Plasmapause and the E-Field

• Electric field choice can greatly influence the
  shape and dynamics of the plasmapause

Liemohn et al., JGR, 2004
19
Plasmapause and The B-Field
Hilmer-Voigt B-Field
T03s B-Field

• Comparison of the RCM-computed plasmapause
  boundary
• Magnetic Field HV95 (left panel) and T03S (right
  panel)
• Plasmasphere is orange, filled at start of
  simulation
• Contour lines flow lines for cold (?0)
  particles
• EUV-extracted plasmapause blue symbols in each
  plot

Slide from Stan Sazykin, Rice U.
20
Plasmaspheric Refilling

• Variable refilling rates
• Slow-then-fast refilling
• Different processes
• Lawrence et al., JGR, 1999
• Field-line distributions
• Flat at the equator
• Does not follow diffusive equilibrium
• Reinisch et al., JGR, 2004

21
Plasmaspheric Mass Density

• Ground-based magnetometers and field-aligned wave
  propagation
• Multiple stations can be used to extract mass
  density along a field line
• These results from the MEASURE mag chain

Berube et al., GRL, 2005
22
Magnetoseismology

• Probing the mass density of the magnetosphere via
  plasma wave transit times

Chi and Russell, GRL, 2005
23
What is Needed for Improvement

• Major Modeling Needs
• Inclusion of heavy ion species
• Inclusion of temperature calculation
• Better coupling with ring current and ionosphere
• Inclusion in global models
• Small-scale structure, subcorotation, and
  refilling still not well understood
• Major Observational Needs
• Routine derivation of TEC from LEO
• Refinement of ULF-wave data analysis techniques
• Establish global ground and space operational
  systems for making coordinated observations in
  time and space
• Follow-on IMAGE-type suite of instruments

24
Ring Current Dynamics
Role of Plasma Sheet Source Population
Role of Driving E and B Fields
Morphology of Storm
Role of Loss Mechanisms
Quantification of Interdependencies?
25
Plasmasphere Dynamics
Subauroral Electric Fields on All Scales
Storm-time Sources Composition Latitude
Longitude
Morphology of Storm
Origin of Plasmaspheric Structures at all Scales?
Losses Internal and External to Storm-Time
Plasmapause
26
Inner Magnetospheric CouplingRing Current and
Plasmasphere
27
Inner Magnetospheric Coupling
Ionospheric Conductance and Dynamics
Large Scale E and B Fields
Ring Current
DE and DB
Precip, J, J
Ionospheric Outflow
Plasma Sheet
Collisions, WPI catalyst
Localized E and B Field Pertubations
Plasma Waves, Seed Pop.
Diagnostic tracers
Heating
Conductivity
DB
Precip.
DE and DB
Diagnostic tracers
Plasmasphere
Radiation Belts
WPI catalyst
ULF Waves
Liemohn, JGR, 2006
28
A Complicated Flow Chart
Liemohn and Khazanov, AGU Mon. 156, 2005
29
Culmination of the IM/S Campaign

• The Inner Magnetosphere/Storms Assessment
  Challenge (the IMSAC)
• The final hurrah of the IM/S Campaign
• Focus the community's efforts on a common goal
• Choose a few specific events for intense study
• Choose a few questions to direct the
  investigations

30
Purpose of the IMSAC

• Goal 1 To what accuracy can the current inner
  magnetospheric models predict the state of the
  fields and plasma?
• Related question What level of model
  sophistication is needed to get a certain level
  of accuracy in the result?
• Goal 2 What is the present consensus
  understanding of inner magnetospheric physics?
• Related question What is the full set of physics
  for a complete description?

31
Storm Selection

• Two storms for the plasmasphere and ring current
• April 22, 2001 cloud with southward IMF
• October 21-23, 2001 sheath/cloud combo
• Two storms for the radiation belts
• October 21-23, 2001 large storm followed by a
  large RB enhancement
• September 4-9, 2002 a series of storms with
  interestnig RB dynamics

32
Culmination of the IMSAC

• JGR-Space Special Section
• Submission deadline was January 9th
• 17 manuscripts submitted
• Some in print/press, most still in
  review/revision
• Over half focused on ring current dynamics
• Please, keep submitting papers
• Additional papers can still be linked to the
  special section in the online listing

33
Conclusions

• GEM IM/S Campaign was a success!
• Focused community effort on plasmasphere and ring
  current issues
• Understanding of magnetic storms is much better
  now
• New questions are plentiful
• Still to do
• Coupling processes between plasma populations
• Self-consistent simulations still need
  improvement
• Coupling to sub-auroral ionosphere
• Coupling to outer magnetosphere
• Understanding small-scale plasma/field structures