• Solar and interplanetary origin of geomagnetic storms

• Sources, acceleration, and losses of ring current ions

• Modeling the evolution of the terrestrial ring current using multi-satellite data

by

Vania K. Jordanova

Space Science Center/EOS

Department of Physics

University of New Hampshire, Durham, USA

New Insights on Geomagnetic Storms From Model Simulations

Using Multi-Spacecraft Data

main recovery phase

Sudden Commencement

Geomagnetic Storm: Ring Current Evolution

• Composition: e-, H+, He+, O+, N+, He++

• Energy Range: ~ 1 keV < E < 300 keV

• Location: ~ 2 < L < 8

• Energy Density: ~ 10 - 1000 keV/cm3

main recovery phase

Sudden Commencement

Geomagnetic Storm: Ring Current Evolution

Solar - Interplanetary - Magnetosphere Coupling

• Flow of plasma within the magnetosphere (convection)

[Gonzalez et al., 1994]

Solar - Interplanetary - Magnetosphere Coupling

• Flow of plasma within the magnetosphere (convection)

[Gonzalez et al., 1994]

Sources of Ring Current Ions

[Chappell et al., 1987]

• Solar wind

• Ionosphere

Sources of Ring Current Ions

[Chappell et al., 1987]

max H+: solar min & quiet conditions

max O+: solar max & active conditions

Total ionospheric flux ~ 10 26 ions/s=> comparable to solar wind source

• Solar wind

• Ionosphere

Ring Current Belt(1-300 keV)Density Isocontours

Dawn

Dusk

Lower Density ColdPlasmaspheric Plasma(Dusk Bulge Region)

( L~6 )( L~8 )

Plasmapause

( L~4)

[Kozyra & Nagy, 1991]

Ring Current Loss Processes

Ring Current Belt(1-300 keV)Density Isocontours

Dawn

Dusk

EnergeticNeutralPrecipitation

Lower Density ColdPlasmaspheric Plasma(Dusk Bulge Region)

( L~6 )( L~8 )

Plasmapause

( L~4)

Charge Exchange

[Kozyra & Nagy, 1991]

Ring Current Loss Processes

Ring Current Belt(1-300 keV)Density Isocontours

Dawn

Dusk

ConjugateSAR Arcs

EnergeticNeutralPrecipitation

AnisotropicEnergeticIon Precipitation

CoulombCollisionsBetweenRing CurrentsandThermals(Shaded Area)

Lower Density ColdPlasmaspheric Plasma(Dusk Bulge Region)

( L~6 )( L~8 )

Plasmapause

( L~4)

Charge Exchange

[Kozyra & Nagy, 1991]

Ring Current Loss Processes

Ring Current Belt(1-300 keV)Density Isocontours

Dawn

Dusk

ConjugateSAR Arcs

EnergeticNeutralPrecipitation

AnisotropicEnergeticIon Precipitation

CoulombCollisionsBetweenRing CurrentsandThermals(Shaded Area)

Lower Density ColdPlasmaspheric Plasma(Dusk Bulge Region)

( L~6 )( L~8 )Wave Scattering of Ring Current Ions

Plasmapause

( L~4)

Isotropic Energetic IonPrecipitation

Ion Cyclotron Waves Charge

Exchange

[Kozyra & Nagy, 1991]

Ring Current Loss Processes

• Single particle motion - describes the motion of a particle under the influence of external electric and magnetic fields

• Magnetohydrodynamics and Multi-Fluid theory - the plasma is treated as conducting fluids with macroscopic variables

• Kinetic theory - adopts a statistical approach and looks at the development of the distribution function for a system of particles

Theoretical Approaches

atm

t

Waves

t

collisCoul

t

chexch

tt

t

F

t

F

t

F

t

F

dt

dF

h o 1

2Ro

ds

1 B s Bms m

sm'

o coso

- radial distance in the equatorial plane from 2 to 6.5 RE

- azimuthal angle from 0 to 360

- kinetic energy from 100 eV to 400 keV

- equatorial pitch angle form 0 to 90

- bounce-averaging (between mirror points)

dV 8 mt3Ro

2 E oh o dRoddEd oFt dN tdV

andwhere

Ro

E

o

Kinetic Model of the Terrestrial Ring Current

• Initial conditions: POLAR and EQUATOR-S data

• Boundary conditions: LANL/MPA and SOPA data

[Jordanova et al., 1994; 1997]

Equatorial exospheric Hydrogen densities [Rairden et al., 1986]

Charge exchange cross sections[Phaneuf et al., 1987; Barnett, 1990]

Charge Exchange Model

Plasmasphere Model

Equatorial plasmaspheric electron density

Ion composition: 77% H+, 20% He+, 3% O+

Plasmasphere Model

Equatorial plasmaspheric electron density

Ion composition: 77% H+, 20% He+, 3% O+

Comparison with geosynchronous LANL data

Wave-Particle Interactions Model

where nt, EII, At are calculated with our kinetic

model for H+, He+, and O+ ions

• Integrate the local growth rate along wave paths and obtain the wave gain G(dB)

tIItg

A,E,n

V

• Solve the hot plasma dispersion relation for EMIC waves:

Wave-Particle Interactions Model

• Solve the hot plasma dispersion relation for EMIC waves:

where nt, EII, At are calculated with our kinetic

model for H+, He+, and O+ ions

• Integrate the local growth rate along wave paths and obtain the wave gain G(dB)

• Use a semi-empirical model to relate G to the wave amplitude Bw:

tIItg

A,E,n

V

dB 20 (neglect) nT 1.0

dB 6020 10

dB 60 nT 10

for

for

for

2060w

G

GB

GB

B Gsat

sat

[Jordanova et al., 2001]

Wave-Particle Interactions Model

• Solve the hot plasma dispersion relation for EMIC waves:

where nt, EII, At are calculated with our kinetic

model for H+, He+, and O+ ions

• Integrate the local growth rate along wave paths and obtain the wave gain G(dB)

• Use a semi-empirical model to relate G to the wave amplitude Bw:

tIItg

A,E,n

V

dB 20 (neglect) nT 1.0

dB 6020 10

dB 60 nT 10

for

for

for

2060w

G

GB

GB

B Gsat

sat

[Jordanova et al., 2001]

WIND Data & Geomagnetic Indices

• Magnetic cloud

• Moderate geomagnetic storm Dst=-83 nT

& Kp=6

Model Results: Dst Index, Jan 10, 1997

Comparison of:

• Kp-dependent Volland-Stern model

• IMF-dependent Weimer model

=> Weimer model predicts larger electric field, which results in larger

injection rate and stronger ring current buildup

Model results & HYDRA data comparison:

• Pitch angle scattering has larger effect than energy diffusion

• Non-local effects of WPI due to transport

Effects of Wave-Particle Interactions

Effects of Collisional Losses

Comparison of model results with POLAR data

Larger effect on: - postnoon spectra - low L shells - high magnetic latitudes - slowly drifting ~1-30 keV ions

• Enhancement in the convection electric field alone is not sufficient to reproduce the stormtime Dst

• The strength of the ring current doubles when the stormtime enhancement of plasmasheet density is considered

Effects of Time-Dependent Plasmasheet Source Population: October 1995

Effects of Inner Magnetospheric Convection:

March 9-13, 1998

Electric potential in the equatorial plane:

• Both models predict strongest fields during the main phase of the storm

• Volland-Stern model is symmetric about dawn/dusk by definition

• Weimer model is more complex and exhibits variable east-west symmetry and spatial irregularities

Modeled H+ Distribution and POLAR Data: March 1998

HYDRA Volland-Stern Model Weimer Model

• East-West transition occurs at lower energy in Volland-Stern model

• Particles follow drift paths at larger distances from Earth and experience less

collisional losses in Weimer model

Bounce-averaged Drift Paths of Ring Current Ions

Ring Current Energization & Dst:

July 13-18, 2000

• A very asymmetric ring current distribution during the main and early recovery phases of the great storm

• Near Dst minimum O+ becomes the dominant ion in agreement with previous observations of great storms

Ring Current Asymmetry & Ion Composition

• Intense EMIC waves from the O+ band are excited near Dst minimum

• The wave gain of the O+ band exceeds the magnitude of the He+ band

• EMIC waves from the O+ band are excited at larger L shells than the He+ band waves

EMIC Waves Excitation

• Data are from the northern pass at ~hour 75

(left) and from the southern pass at ~hour

93 (right), MLT~16

• Isotropic pitch angle distributions, indicating

strong diffusion scattering are observed at

large L shells near Dst minimum

• Partially filled loss cones, indicating

moderate diffusion are observed at lower L

shells and during the recovery phase

Ion Pitch Angle Distributions from POLAR/IPS

L=7

L=6

L=5

L=4

L=3

Model Results: Precipitating Proton FluxHour 75

• Precipitating H+ fluxes are significantly enhanced by wave-particle interactions

• Their temporal and spatial evolution is in good agreement with POLAR/IPS data

Model Results: Precipitating Proton FluxHour 75 Hour 93

• Proton precipitation losses increase by more than an order of magnitude when WPI are considered

• Losses due to charge exchange are, however, predominant

Proton Ring Current Energy Losses

The ring current is a very dynamic region that couples the magnetosphere and the ionosphere during geomagnetic storms

New results emerging from recent simulation studies were discussed:

• the effect of the convection electric field on ring current dynamics: influence on Dst index, east-west transition energy, dips in the distribution function

• the important role of the stormtime plasmasheet enhancement for ring current buildup

• the formation of an asymmetric ring current during the main and early recovery storm phases

• it was shown that charge exchange is the dominant ring current loss process

• wave-particle interactions contribute significantly to ion precipitation, however, their effect on the total energy balance of the ring current population is only ~2-8% reduction

More studies are needed

• to determine the effect of WPI on the heavy ion components, moreover O+ is the dominant ring current specie during great storms

• to determine the contribution of substorm induced electric fields on ring current dynamics

Conclusions

Many thanks are due to:

C. Farrugia, L. Kistler, M. Popecki, and R. Torbert,

Space Science Center/EOS, University of New Hampshire, Durham

R. Thorne, Department of Atmospheric Sciences, UCLA, CA

J. Fennell and J. Roeder, Aerospace Corporation, Los Angeles, CA

M. Thomsen, J. Borovsky, and G. Reeves, Los Alamos Nat Laboratory, NM

J. Foster, MIT Haystack Observatory, Westford, MA

R. Erlandson, Johns Hopkins University, APL, Laurel, MD

K. Mursula, University of Oulu, Oulu, Finland

This research has been supported in part by NASA under grants NAG5-7804,

NAG5-4680, NAG5-8041 and NSF under grant ATM 0101095

Acknowledgments