Ring Current and Plasmasphere
Accomplishments
During the GEM
IM/S Campaign
Mike Liemohn
GEM Workshop Tutorial
June 27, 2006
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?
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
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, Gradientcurvature terms
• Important: Dominates the energy density of the
inner magnetosphere
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
Ring Current Morphology
Bz, GSE (nT)
IMF
• The ring current is not a ring during storms
Liemohn et al., JGR, 2001
31 March 2001
40
20
0
-20
-40
-60
0
06:00
12:00
18:00
24:00 UT
From Don
Mitchell
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
Electric Field Connection
• Partial ring current causes a potential well
near midnight, changing the hot ion drift
paths in the inner magnetosphere
Postmidnight
enhancement
8 UT 12 August 2000
Fok et al., SSR, 2003
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
Magnetic Field Connection
2x1030
30
1.6x10
30
1.2x10
29
8x10
4x1029
0
30
2x10
1.6x1030
30
1.2x10
29
8x10
4x1029
0
30
2x10
1.6x1030
30
1.2x10
29
8x10
29
4x10
0
Dst observed, nT
– 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
Ring current energy, keV
• One-way connection: Bfield influences on the
ring current
Particle Tracing Model
With Inductive-E Pulses
dipole
1-300 keV
20-80 keV
80-300 keV
1-30 keV
dipole + T89
dipole + T01s
80
0
-80
0 6 12 18 0
Apr 21
6 12 18 0
Apr 22
UT
6 12 18 24
Apr 23
Ganushkina et al., JGR, 2006
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
The Flip Side of Feeback:
Effect 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
Without Kinetic Code
With Kinetic Code
From Toth, Ridley, and De Zeeuw
Plasma Sheet Connection
• Plasma sheet density controls the strength
of the ring current
• Plasma sheet temperature also affects ring
current intensity
Liemohn and Ridley, JGR 2002
Ebihara & Ejiri, JGR, 2000
Plasma Wave Connection
• Calculating the EMIC wave energy density selfconsistently 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
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
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
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
Plasmapause and the E-Field
• Electric field choice can greatly influence
the shape and dynamics of the plasmapause
Liemohn et al.,
JGR, 2004
Plasmapause and The B-Field
Hilmer-Voigt B-Field
T03s B-Field
• Comparison of the RCM-computed plasmapause boundary
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–
–
–
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.
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
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
Magnetoseismology
• Probing the mass density of the magnetosphere via
plasma wave transit times
Chi and Russell, GRL, 2005
What is Needed for Improvement
• Major Modeling Needs:
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–
–
–
–
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
Ring Current Dynamics
Role of Plasma Sheet
Source Population
Role of Driving
E and B Fields
Morphology of Storm
Quantification of
Interdependencies?
Role of Loss
Mechanisms
Plasmasphere Dynamics
Storm-time Sources:
Composition & Latitude &
Longitude
Subauroral
Electric Fields on
All Scales
Morphology of Storm
Origin of
Plasmaspheric
Structures at
all Scales?
Losses Internal and External to
Storm-Time Plasmapause
Inner Magnetospheric Coupling:
Ring Current and Plasmasphere
E and B Fields
Ring Current
Collisions, WPI catalyst
Heating
Plasmasphere
Inner Magnetospheric Coupling
Plasma
Sheet
Precip, J, J||
Ring Current
DE and DB
Large Scale E
and B Fields
Localized
E and B Field
Pertubations
Ionospheric
Conductance
and Dynamics
Ionospheri
c
Outflow
Diagnostic tracers
Radiation Belts
WPI catalyst
ULF Waves
Plasmasphere
Liemohn, JGR, 2006
A Complicated Flow Chart
Liemohn and Khazanov, AGU Mon. 156, 2005
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
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?
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
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
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
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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