New Insights on Geomagnetic Storms From Model Simulations Using Multi-Spacecraft Data

1. New Insights on Geomagnetic Storms From Model Simulations Using Multi-Spacecraft Data by Vania K. Jordanova Space Science Center/EOS Department of Physics University of New Hampshire, Durham, USA • • 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

2. Geomagnetic Storm: Ring Current Evolution Sudden Commencement main recovery phase

3. Geomagnetic Storm: Ring Current Evolution Sudden Commencement • • 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

4. • Flow of plasma within the magnetosphere (convection) Solar - Interplanetary - Magnetosphere Coupling [Gonzalez et al., 1994]

5. • Flow of plasma within the magnetosphere (convection) Solar - Interplanetary - Magnetosphere Coupling [Gonzalez et al., 1994]

6. Sources of Ring Current Ions • • Solar wind • • Ionosphere [Chappell et al., 1987]

7. Sources of Ring Current Ions • • Solar wind • • Ionosphere [Chappell et al., 1987] max H+: solar min & quiet conditions max O+: solar max & active conditions Total ionospheric flux ~ 1026ions/s => comparable to solar wind source

8. Ring Current Loss Processes Ring Current Belt (1-300 keV) Density Isocontours Plasmapause Lower Density Cold Plasmaspheric Plasma (Dusk Bulge Region) Dawn ( L~4) Dusk ( L~8 ) ( L~6 ) [Kozyra & Nagy, 1991]

9. Ring Current Loss Processes Energetic Ring Current Belt (1-300 keV) Density Isocontours Neutral Plasmapause Precipitation Lower Density Cold Plasmaspheric Plasma (Dusk Bulge Region) Dawn Charge Exchange ( L~4) Dusk ( L~8 ) ( L~6 ) [Kozyra & Nagy, 1991]

10. Ring Current Loss Processes Energetic Ring Current Belt (1-300 keV) Density Isocontours Neutral Plasmapause Precipitation Lower Density Cold Plasmaspheric Plasma (Dusk Bulge Region) Dawn Charge Exchange Coulomb Conjugate Collisions SAR Arcs Between Ring Currents ( L~4) and Dusk Thermals Anisotropic (Shaded Area) Energetic Ion Precipitation ( L~8 ) ( L~6 ) [Kozyra & Nagy, 1991]

11. Ring Current Loss Processes Energetic Ring Current Belt (1-300 keV) Density Isocontours Neutral Plasmapause Precipitation Lower Density Cold Plasmaspheric Plasma (Dusk Bulge Region) Dawn Ion Cyclotron Charge Waves Exchange Coulomb Conjugate Collisions SAR Arcs Between Ring Currents ( L~4) and Dusk Thermals Anisotropic (Shaded Area) Energetic Ion Precipitation ( L~8 ) ( L~6 ) Wave Scattering of Ring Current Ions Isotropic Energetic Ion [Kozyra & Nagy, 1991] Precipitation

12. Theoretical Approaches • • Single particlemotion - 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

13. Kinetic Model of the Terrestrial Ring Current • •Initial conditions: POLAR and EQUATOR-S data • •Boundary conditions: LANL/MPA and SOPA data where and - 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) [Jordanova et al., 1994; 1997]

14. Charge Exchange Model Equatorial exospheric Hydrogen densities [Rairden et al., 1986] Charge exchange cross sections [Phaneuf et al., 1987; Barnett, 1990]

15. Plasmasphere Model Equatorial plasmaspheric electron density Ion composition: 77% H+, 20% He+, 3% O+

16. Plasmasphere Model Comparison with geosynchronous LANL data Equatorial plasmaspheric electron density Ion composition: 77% H+, 20% He+, 3% O+

17. 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)

18. 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: [Jordanova et al., 2001]

19. 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: [Jordanova et al., 2001]

20. WIND Data & Geomagnetic Indices • •Magnetic cloud • •Moderate geomagnetic storm Dst=-83 nT & Kp=6

21. 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

22. Effects of Wave-Particle Interactions • Model results & HYDRA data comparison: • • Pitch anglescattering has larger effect thanenergydiffusion • • Non-localeffects of WPI due to transport

23. 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

24. Effects of Time-Dependent Plasmasheet Source Population: October 1995 • • Enhancement in the convection electric fieldalone is not sufficient to reproduce the stormtime Dst • •The strength of the ring current doubles when the stormtime enhancement of plasmasheet densityis considered

25. 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 • •Weimermodel is more complex and exhibits variable east-west symmetry and spatial irregularities

26. Modeled H+ Distribution and POLAR Data: March 1998 HYDRA Volland-Stern Model Weimer Model

27. Bounce-averaged Drift Paths of Ring Current Ions • • East-West transitionoccurs at lower energy inVolland-Sternmodel • • Particles follow drift paths at larger distances from Earth and experience lesscollisional lossesinWeimermodel

28. Ring Current Energization & Dst:July 13-18, 2000

29. Ring Current Asymmetry & Ion Composition • • 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

30. EMIC Waves Excitation • • 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

31. Ion Pitch Angle Distributions from POLAR/IPS L=7 • • 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 L=6 L=5 L=4 L=3

32. Hour 75 Model Results: Precipitating Proton Flux

33. Hour 75 Hour 93 Model Results: Precipitating Proton Flux • • Precipitating H+ fluxes are significantly enhanced by wave-particle interactions • • Their temporal and spatial evolution is in good agreement with POLAR/IPS data

34. Proton Ring Current Energy Losses • • Proton precipitation losses increase by more than an order of magnitude when WPI are considered • • Losses due to charge exchange are, however, predominant

35. Conclusions • Thering currentis a very dynamic region that couples the magnetosphere and the ionosphere during geomagnetic storms • New resultsemerging from recent simulation studies were discussed: • • the effect of theconvection electric fieldon ring current dynamics: influence on Dst index, east-west transition energy, dips in the distribution function • • the important role of the stormtime plasmasheet enhancementfor ring current buildup • • the formation of anasymmetricring current during the main and early recovery storm phases • • it was shown that charge exchangeis the dominant ring current loss process • • wave-particle interactionscontribute 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, moreoverO+is the dominant ring current specie during great storms • • to determine the contribution of substorminduced electric fieldson ring current dynamics

36. Acknowledgments • 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