html5-img
1 / 40

Modeling Geomagnetic Storm Dynamics

Modeling Geomagnetic Storm Dynamics . by Vania K. Jordanova Space Science Center/EOS Department of Physics University of New Hampshire, Durham, USA. • Origin, growth, and recovery of geomagnetic storms • Theoretical approaches for studying inner magnetosphere dynamics

benjamin
Télécharger la présentation

Modeling Geomagnetic Storm Dynamics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Modeling Geomagnetic Storm Dynamics by Vania K. Jordanova Space Science Center/EOS Department of Physics University of New Hampshire, Durham, USA • • Origin, growth, and recovery of geomagnetic storms • • Theoretical approaches for studying inner magnetosphere dynamics • • New insights on geomagnetic storms from kinetic model simulations using multi-satellite data • • Future model developments Tutorial, GEM Workshop, 6/27/03 1

  2. Sources of ring current ions Solar - Interplanetary - Magnetosphere Coupling [Gonzalez et al., 1994] [Chappell et al., 1987] • Solar wind • Ionosphere max H+: solar min & quiet conditions max O+: solar max & active conditions Tutorial, GEM Workshop, 6/27/03 2

  3. Magnetic Field of the Earth [Hess, 1968] • The main geomagnetic field can be represented by spherical harmonic series in which the first term is the simple dipole term [Gauss, 1839]. Temporal variations of the internal field are modeled by expanding the coefficients in Taylor series in time [e.g., IGRF model, 1995]. • The Earth's real magnetic field is the sum of several contributions including the main (internal) field and the external source (magnetospheric) fields [e.g., Tsyganenko, 1996, 2001]. • Gradient-Curvature velocity: Tutorial, GEM Workshop, 6/27/03 3

  4. Large-Scale Magnetospheric Electric Field • Volland-Stern semiempirical model • convection potential: • corotation potential: • Drift velocity: Cluster/EDI Data IMF Bz<0, 1Re=0.2 mV/m [Matsui et al., 2003] [Lyons and Williams, 1984] Tutorial, GEM Workshop, 6/27/03 4

  5. Cluster/EDI Electric Field Data • • Statistically averaged data at L=4-5, IMF Bz<0, average Kp=2+, corotating frame of reference • • Radial and azimuthal components mapped to equatorial plane • • Strong electric field at MLT=19-22, not observed during northward IMF [Matsui et al., 2003] Tutorial, GEM Workshop, 6/27/03 5

  6. Diffusive Transport • • Standard model [e.g., Sheldon and Hamilton, 1993] • - magnetic diffusion [Falthammer, 1965] • - electric diffusion [Cornwall, 1971] • • The cross-tail potential is enhanced by a superposition of exponentially decaying impulses [Chen et al., 1993; 1994] • • Profiles of normalized ring current energy density indicate the impulsive character of enhancements makes significant contribution in storms with long main phase [Chen et al., 1997] Tutorial, GEM Workshop, 6/27/03 6

  7. 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 Tutorial, GEM Workshop, 6/27/03 7

  8. Theoretical Approaches • • Single particlemotion - describes the motion of a particle under the influence of external electric and magnetic fields • - trajectory tracing studies [e.g., Takahashi & Iyemori, 1989; Ebihara & Ejiri, 2000] • - mapping of distribution function [e.g., Kistler et al., 1989; Chen et al. 1993] • • Magnetohydrodynamics and Multi-Fluid theory - the plasma is treated as conducting fluids with macroscopic variables, allow self-consistent coupling of the magnetosphere and ionosphere • - Rice convection model [e.g., Harel et al., 1981; Wolf et al., 1981; 1997] • • Kinetic theory - adopts a statistical approach and looks at the development of the distribution function for a system of particles [e.g., Fok et al., 1993; Sheldon & Hamilton, 1993; Jordanova et al., 1994] Tutorial, GEM Workshop, 6/27/03 8

  9. Kinetic Model of the Ring Current - Atmosphere Interactions (RAM) • •Initial conditions: POLAR, CLUSTER and EQUATOR-S data • •Boundary conditions: LANL/MPA and SOPA data [Jordanova et al., 1994; 1997] Ro - radial distance in the equatorial plane from 2 to 6.5 RE -azimuthal angle from 0 to 360, E - kinetic energy from 100 eV to 400 keV o- equatorial pitch angle from 0 to 90 - bounce-averaging (between mirror points) Tutorial, GEM Workshop, 6/27/03 9

  10. Model: Drift of Ring Current Particles Initial E=0.2 keV at L=10Initial E=0.4 keV at L=10 The 90 deg pitch angle particle tracings. Asteriks are plotted at 1 hour steps within 20 hours [Ejiri, 1978] Tutorial, GEM Workshop, 6/27/03 10

  11. Model: Ring Current Loss Processes Charge exchange with Hydrogen from geocorona (A) (A+) - cross section for charge exchange with H - bounce-averaged exospheric Hydrogen density [Schulz and Blake, 1990] Loss of particles to the atmosphere due to the emptying of the loss cone (twice per bounce period B) [Lyons, 1973] , where Tutorial, GEM Workshop, 6/27/03 11

  12. Model: Ring Current Loss Processes Coulomb collisions with thermal plasma: - Fokker-Planck equation considering energy degradation & pitch angle scattering - plasmaspheric density model for e-, H+, He+, O+species [Rasmussen et al., 1993] Plasma waves scattering: quasi-linear theory [Kennel and Engelmann, 1966; Lyons and Williams, 1984] - quasi-linear diffusion coefficients including heavy ion components [Jordanova et al., 1996] Tutorial, GEM Workshop, 6/27/03 12

  13. Plasmasphere Model Equatorial plasmaspheric electron density Ion composition: 77% H+, 20% He+, 3% O+ Tutorial, GEM Workshop, 6/27/03 13

  14. EMIC Waves Observations EMIC waves recorded using DE1 magnetometer within 30° MLAT during the 10-year mission lifetime [Erlandson and Ukhorskiy, 2001] • Freja data, April 2-8, 1993 storm, Dst=-170 nT, Kp=8- • •Waveamplitudesdecreased with storm evolution • •Wavesbelow O+ gyrofrequencyobserved near Dst minimum [Braysy et al., 1998] Tutorial, GEM Workshop, 6/27/03 14

  15. Self-consistent Wave-Particle Interactions Model (1) 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 (2) Integrate the local growth rate along wave paths and obtain the wave gain G(dB) a) Use a semiempirical model to relate G to the wave amplitude Bw: b) Or, use the analytical solution of the wave equation to relate G to the wave amplitude: Bw=Boexp(G), where Bo is a background noise level [Jordanova et al., 2001] Tutorial, GEM Workshop, 6/27/03 15

  16. IMAGE Mission: Imaging the inner magnetosphere • •Simultaneous global images of the plasmasphere and the ring current during the storm main phase (Dst= -133 nT) on May 24, 2000 [Burch et al., 2001] EUV image of the plasmasphere at 0633 UT from above the north pole Superimposed HENA image of 39-60 keV fluxes showing significant ion precipitation near dusk • •The low altitude ENA fluxes peak near dusk and overlap the plasmapause [Burch et al., 2001] Tutorial, GEM Workshop, 6/27/03 16

  17. WIND Data & Geomagnetic Indices:January 9-11, 1997 • •An interplanetary shock arrived at Wind at hour~25 • • It is driven by a magnetic cloud which extends from hour~29 to hour~51 • • Triggered a moderate geomagnetic storm with Dst= -83 nT & Kp=6 Tutorial, GEM Workshop, 6/27/03 17

  18. Convection Electric Field: Comparison with POLAR/EFI Data • Enhanced electric fields are measured below L=5 during the main phase of the storm on the duskside (MLT18) • Such electric fields appear about an hour or more before a strong ring current forms • Much smaller electric fields at larger L shells (L=5-8) and on the dawnside (MLT6) • Good agreement with the MACEP model we developed on the basis of the ionospheric AMIE [Richmond, 1992] model and a penetration electric field [Ridley and Liemohn, 2002] [Boonsiriseth et al., 2001] Tutorial, GEM Workshop, 6/27/03 18

  19. Effects of Inner Magnetospheric Convection: January 10-11, 1997 • 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 • •MACEPmodel is more complex and exhibits variable east-west symmetry and spatial irregularities Tutorial, GEM Workshop, 6/27/03 19

  20. Ring Current Asymmetry: Main Phase • • Initial ring current injection at high L shells on the duskside • • A very asymmetric ring current distribution during the main phase of the storm due to freshly injected particles on open drift paths • The total energy density peaks near midnight using MACEP, near dusk using Volland-Stern • Ring current ions penetrate to lower L shells and gain larger energy in MACEP than in Volland-Stern Tutorial, GEM Workshop, 6/27/03 20

  21. Ring Current Asymmetry: Recovery Phase • • Energy density peaks near dusk in both MACEP and Volland-Stern models during early recovery phase • The trapped population evolves into a symmetric ring current during late recovery phase Tutorial, GEM Workshop, 6/27/03 21

  22. Model Results: Dst Index, Jan 10, 1997 • Comparison of: • •Kp-dependent Volland-Stern model • • Empirical MACEP model • => MACEP model predicts larger electric field, which results in larger injection rate and stronger ring current buildup Tutorial, GEM Workshop, 6/27/03 22

  23. Modeled Distributions and POLAR Data: Jan 10, 09:30 UT Tutorial, GEM Workshop, 6/27/03 23

  24. Ion Pitch Angle Distributions: POLAR/IPS • • Data are from the southern pass at MLT~6 and E=20 keV on Jan 9 (left), 10 (middle) and 11 (right) • • Empty loss cones, indicating no pitch angle diffusion are observed at these locations Tutorial, GEM Workshop, 6/27/03 24

  25. Ion Pitch Angle Distributions: POLAR/IPS • • Data are from the southern pass at MLT~18 and E=20 keV at hour~8.5 (middle) and at hour~25.5 (right) • • 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 during the recovery phase Tutorial, GEM Workshop, 6/27/03 25

  26. EMIC Waves Excitation:January 10, 1997 • • We calculated the wave growth of EMIC waves from the He+ band (between O+ and He+ gyrofrequency) • • Comparable wave growth is predicted by both models during the early main phase • • Intense waves are excited near Dst minimum and during the recovery phase only whenMACEPmodel is used Tutorial, GEM Workshop, 6/27/03 26

  27. Hour 9 Model Results: Precipitating Proton Flux Hour 25 • • Precipitating H+ fluxes are significantly enhanced by wave-particle interactions • • Their temporal and spatial evolution is in good agreement with POLAR/IPS data at low L shells 27 Tutorial, GEM Workshop, 6/27/03

  28. Effects of Plasma Sheet Variability: March 30 - April 3, 2001 • • An interplanetary (IP) shock is detected by ACE at ~0030 UT on March 31 • • A great geomagnetic storm Dst= -360 nT (SYM-H= -435 nT) and Kp=9- occurs Tutorial, GEM Workshop, 6/27/03 28

  29. LANL Boundary conditions: March - April, 2001 • • Enhanced fluxes are observed in both energy channels of the MPA instrument for ~10 hours after the IP shock • • The magnitude of the ion fluxes gradually decreases after that • • The MPA plasma sheet ion density shows a similar trend Tutorial, GEM Workshop, 6/27/03 29

  30. Effects of Time-Dependent Plasma Sheet Source Population: March 30 - April 3, 2001 • • Enhancement in the convection electric fieldalone is not sufficient to reproduce the Dst index • •The ring current (RC) increases significantly when the stormtime enhancement of plasma sheet density is considered • •The drop of plasma sheet density during early recovery phase is important for the fast RC decay [Jordanova et al., GRL, 2003] 30 Tutorial, GEM Workshop, 6/27/03

  31. EMIC Waves Excitation:July 13-18, 2000 • • 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 [Jordanova et al., Solar Physics, 2001] Tutorial, GEM Workshop, 6/27/03 31

  32. 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 [Jordanova, Space Sci. Rev., 2003] 32 Tutorial, GEM Workshop, 6/27/03

  33. IMAGE/HENA Data, courtesy of Mona Kessel, NASA Tutorial, GEM Workshop, 6/27/03 33

  34. RAM Simulations, movie prepared at NASA, Nov 2000 Tutorial, GEM Workshop, 6/27/03 34

  35. Relativistic Electron Kinetic Model • g - relativistic factor, mo - rest mass, p - relativistic momentum of particle • - radial diffusion coefficients Tutorial, GEM Workshop, 6/27/03 35

  36. Relativistic Electron Transport and Loss • Radial diffusion coefficients [Brautigam and Albert, 2000] • • magnetic field fluctuation • electric field fluctuation • Wave-particle interactions (WPI) • • within plasmasphere [Lyons, Thorne, and Kennel, 1972] • n=±5 cyclotron and Landau resonance • hiss and lightning whistler (10 pT - [Abel and Thorne, 1998; Albert, 1999] • • outside plasmasphere – • E>Eo : empirical scattering rate [Chen and Schulz, 2001] • E<Eo : strong diffusion scattering rate [Schulz, 1974] • Boundary conditions: LANL/MPA and SOPA data Tutorial, GEM Workshop, 6/27/03 36

  37. RAM Electron Results: Test simulations Tutorial, GEM Workshop, 6/27/03 37

  38. Model Results and NOAA Data: October 21-25, 2001 [Miyoshi et al., 2003] Tutorial, GEM Workshop, 6/27/03 38

  39. 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 predominant role of theconvection electric fieldfor ring current dynamics & Dst index • • the importance of the stormtime plasma sheet enhancement and dropoutfor ring current buildup and decay • • the formation of anasymmetricring current during the main and early recovery storm phases • • it was shown that charge exchangeis the dominant internal ring current loss process • • wave-particle interactionscontribute significantly to ion precipitation, however, their effect on the total energy balance of the ring current H+ population is small (~10% reduction) • Future studies • • determine the effect of WPI on the heavy ion components, moreoverO+is the dominant ring current specie during great storms • • study effects of diffusive transport and substorm-induced electric fieldson ring current dynamics • • determine the role of a more realistic magnetic field model • • development of a relativistic electron model Tutorial, GEM Workshop, 6/27/03 39

  40. Acknowledgments • Many thanks are due to: • Yoshizumi Miyoshi, Tohoku University, Japan, & UNH, Durham, USA • R. Thorne, A. Boonsiriseth, Y. Dotan,Department of Atmospheric Sciences, UCLA, CA • M. Thomsen, J. Borovsky, and G. Reeves, Los Alamos Nat Laboratory, NM • J. Fennell and J. Roeder,Aerospace Corporation, Los Angeles, CA • H. Matsui, C. Farrugia, L. Kistler, M. Popecki, C. Mouikis, J. Quinn, R. Torbert, • Space Science Center/EOS, University of New Hampshire, Durham, NH • This research has been supported in part by NASA under grants NAG5-13512, NAG5-12006 and NSF under grant ATM 0101095 Tutorial, GEM Workshop, 6/27/03 40

More Related