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