ring current and plasmasphere accomplishments during the gem im/s campaign mike liemohn gem workshop...
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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, Gradient-curvature 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• The ring current is not a ring during storms
Liemohn et al., JGR, 2001
-60
-40
-20
0
20
40
0 06:00 12:00 18:00 24:00 UT
31 March 2001
From Don Mitchell
Ring Current-FAC- 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
8 UT 12 August 2000
Post-midnight enhance-
ment
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, 2002Chen et al., JGR, 2003
04x10298x1029
1.2x10301.6x1030
2x1030
-80
0
80
Dst observed, nT
1-300 keV
20-80 keV
1-30 keV
80-300 keV
04x10298x1029
1.2x10301.6x1030
2x1030
Ring current energy, keV
04x10298x1029
1.2x10301.6x1030
2x1030
dipole
dipole + T89
dipole + T01s
0 6 12 18 0 6 12 18 0 6 12 18 24 Apr 21 Apr 22 Apr 23 UT
Ganushkina et al., JGR, 2006
Magnetic Field Connection
• 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
Particle Tracing ModelWith Inductive-E Pulses
Zaharia et al., JGR, 2005
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
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
With Kinetic CodeWithout Kinetic Code
From Toth, Ridley, and De Zeeuw
Ebihara & Ejiri, JGR, 2000Liemohn and Ridley, JGR 2002
Plasma Sheet Connection• Plasma sheet density controls the strength
of the ring current
• Plasma sheet temperature also affects ring current intensity
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 – Preference for field-aligned
• 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
Slide from Stan Sazykin, Rice U.
Plasmapause and The 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
Hilmer-Voigt B-Field T03s B-Field
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:
– 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
Role of Loss Mechanisms
Morphology of Storm
Quantification of Interdependencies?
Plasmasphere Dynamics
Subauroral Electric Fields on All Scales
Storm-time Sources: Composition & Latitude & Longitude
Losses Internal and External to Storm-Time Plasmapause
Morphology of Storm
Origin of Plasmaspheric Structures at all Scales?
Inner Magnetospheric Coupling:Ring Current and Plasmasphere
Ring Current
E and B Fields
Plasmasphere
Locali
zed
IM p
ertu
rb.
J , J ||
Heating
Localized IM perturb.
Conductivity
Collisions, WPI catalyst
Inner Magnetospheric Coupling
Ring Current
LocalizedE and B FieldPertubations
Plasmasphere
Conductivity
Collisions, WPI catalyst
E and B
Heating
Radiation Belts
Pre
cip,
J, J
||
E a
nd
B
Diagnostic tracersPrecip
.
WPI catalyst
BD
iagn
ostic
trac
ers
Plas
ma
Wav
es, S
eed
Pop.
Ionospheric Conductance
and Dynamics
Ionospheric
OutflowPlasma Sheet
ULF Waves
Large Scale E and B Fields
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– 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