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

mainrecovery 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: ~ keV/cm 3 mainrecovery 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 ~ ions/s => comparable to solar wind source Solar wind Ionosphere

Ring Current Belt (1-300 keV) Density Isocontours Dawn Dusk Lower Density Cold Plasmaspheric 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 Energetic Neutral Precipitation Lower Density Cold Plasmaspheric 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 Conjugate SAR Arcs Energetic Neutral Precipitation Anisotropic Energetic Ion Precipitation Coulomb Collisions Between Ring Currents and Thermals (Shaded Area) Lower Density Cold Plasmaspheric 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 Conjugate SAR Arcs Energetic Neutral Precipitation Anisotropic Energetic Ion Precipitation Coulomb Collisions Between Ring Currents and Thermals (Shaded Area) Lower Density Cold Plasmaspheric Plasma (Dusk Bulge Region) ( L~6 )( L~8 ) Wave Scattering of Ring Current Ions Plasmapause ( L~4) Isotropic Energetic Ion Precipitation 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

- radial distance in the equatorial plane from 2 to 6.5 R E - 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) andwhere 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 n t, E II, A t 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) Solve the hot plasma dispersion relation for EMIC waves:

Wave-Particle Interactions Model Solve the hot plasma dispersion relation for EMIC waves: where n t, E II, A t 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 B w : [Jordanova et al., 2001]

Wave-Particle Interactions Model Solve the hot plasma dispersion relation for EMIC waves: where n t, E II, A t 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 B w : [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 HYDRAVolland-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 Flux Hour 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 Flux Hour 75Hour 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, NAG and NSF under grant ATM Acknowledgments