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New Insights on Storm-Time Ring Current and Radiation Belt Modeling

New Insights on Storm-Time Ring Current and Radiation Belt Modeling. Vania K. Jordanova Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.

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New Insights on Storm-Time Ring Current and Radiation Belt Modeling

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  1. New Insights on Storm-Time Ring Current and Radiation Belt Modeling Vania K. Jordanova Space Science and Applications, Los Alamos National Laboratory, Los Alamos, NM 87545, USA • Discuss simulations of the ring current and the radiation belts during the geomagnetic storms of April 21 and October 21, 2001 • Investigate the relative effect on the dynamics of energetic particles of the: - convection electric field - radial diffusion - self-consistent magnetic field calculation • Acquire knowledge for the development of a predictive geomagnetic storm model Acknowledgments: Y. Miyoshi, Solar-Terrestrial Environment Laboratory, Nagoya, Japan S. Zaharia, B. Lavraud, and M. Thomsen, Los Alamos National Laboratory, NM A. Vapirev, C. Mouikis, and H. Matsui, University of New Hampshire, Durham, NH D. Evans, SEC/NOAA, Space Environment Lab, Boulder, CO SM24D-01, WPGM 2006

  2. Ring Current - Atmosphere Interactions Model RAM --- Jordanova et al. [1996; 2001] Calculates the distribution function of ring current H+, O+, and He+ ions and thermal plasma from the fundamental kinetic equations plasma sheet - LANL sources initial distribution - Polar charge exchange Ring current model Coulomb collisions losses E=100 eV – 400 keV PA= 0º – 90º dipole (L= 2.0-6.5) all MLT atmospheric loss w-p interactions escape from MP transport convection Plasmasphere model ionosphere/thermosphere

  3. Recent Model Development: Relativistic Electrons Radial diffusion:classical diffusion theory [Cornwall, 1971; Schulz and Lanzerotti, 1974] where are radial diffusion coefficients from [Brautigam and Albert, 2000] Electron scattering by plasma waves:simplified loss term • within plasmasphere - hiss and lightning whistler [Lyons et al., 1972; Abel and Thorne, 1998; Albert, 1999] • outside plasmasphere – strong diffusion [Schulz, 1974] and empirical scattering rate [Chen and Schulz, 2001] Boundary conditions:LANL/MPA and SOPA data

  4. Interplanetary Observations and Geomagnetic Indices: October 21-25, 2001 • An interplanetary shock was observed at ~16 UT, October 21 • IMF Bz~-20 nT & solar wind speed v~700km/s; a 2nd negative Bz~-15 nT excursion at hour~33 • Triggered a large geomagnetic storm with Dst=-180 nT; strong geomagnetic activity lasting for about a day • Two enhancements of Kp=8- and Kp=7+ occurred at hour~22 and hour~40

  5. Cluster/CODIF Data: October 21, 2001 • Energy spectra and pitch angle spectra for H+, He+ and O+ in the prenoon sector as the S/C goes toward perigee (4.0 Re) during the main phase of the storm • The energy spectra clearly show the deep minimum at about 10 keV in all species At high energies H+ peak @ 90 degrees Low energy O+ and He+ outflow In the inner magnetosphere field aligned low energy O+ from both hemispheres

  6. Cluster EDI & EFW Data and Model Comparison Electric field in the equatorial plane during the storm main phase: •The fields are mapped to the SM magnetic equator for each 4 s using the Tsyganenko magnetic field model; signatures of ULF (Pc5) waves are seen • The solid red line indicates 10-min running averages of the data •Weimermodel reproduces very well the radial component but not the azimuthal electric field component

  7. RAM Comparison with Cluster/CIS Data: H+ and O+ • The Volland-Stern model (dashed) underestimates the distribution within the stagnation dip at low L • Adding radial diffusion (dash-dot) smooths the gradients and reduces the dip • The Weimer model (solid) reproduces better the observations

  8. RAM Comparison with NOAA Data: Ions • Pronounced enhancement near dusk with both models at low energies • Weimer model reproduces better the the enhancement at higher energies

  9. Ring Current Energization and Dst Index Comparison of: •Kp-dependent Volland-Stern model • IMF-dependent Weimer model • Weimer model & Radial diffusion => Weimer model predicts larger electric field than Volland-Stern throughout the main phase, which results in larger injection rate and stronger ring currentbuildup => Both models underestimate ring current energization near the 2ndDst minimum => An additional injection of ring current particles near 2ndDst minimum by radial diffusion improves the agreement with observations

  10. RAM Electron Results • Enhancement near dawn for lower energies electrons • Good agreement with NOAA electron data [Miyoshi et al., JGR, 2006]

  11. Time Variation of Electron Energy Gain

  12. Contribution of Ring Current Electrons • Theelectroncontribution is small (~2%) during quiet times and reaches maximum values of~10%near Dst minima • Radial diffusioninjects high-energy particles deep into the magnetosphere (L<4) and increases the total ring current energy by~15%near minimum Dst

  13. Interplanetary Observations and Geomagnetic Indices: April 21-23, 2001 • An interplanetary shock was observed at ~16 UT, April 21 • IMF Bz~-15 nT & solar wind speed v~400km/s • The magnetic cloud triggered a moderate geomagnetic storm with >12 hour long main phase, Dst=-100 nT and Kp=6+ • Slow storm recovery lasting more than a day

  14. IMAGE/HENA Proton Flux (27-39 keV) April 22 08 UT 05 UT 16 UT [courtesy of the IMAGE/HENA team, P. Brandt]

  15. Plasmasphere Evolution & IMAGE/EUV Data Plasmapause obtained from IMAGE/EUV data [Goldstein et al., 2005] Modelplasmapause LANL cold plasma data • Both VS and W01 models reproduce well the plasmapause observed by IMAGE on the nightside • Weimer model produces narrower dayside plumes

  16. Ring Current H+ Flux, April 22 Hour 40 • Pronounced ring current asymmetry during the main phase showing peaks on the nightside in agreement with HENA data • The fluxes are larger using Weimer model which injects particles deeper in the inner magnetosphere • Radial diffusion enhances only the high-energy proton fluxes

  17. Further Model Development: Non-dipole magnetic field • Relative difference between the dipole field and the T04 magnetic field during (left) quiet and (right) disturbed times in the SM equatorial plane • The dipole field is larger on the dusk-midnight side and smaller on the dawn-noon side • The bounce-averaged gradient curvature velocity increases on the dusk-midnight side in the non-dipole case Sun Sun [Vapirev & Jordanova, 2006]

  18. Further Model Development: Self-consistent magnetic field • Using a 3-D equilibrium code [Zaharia et al., 2005] the magnetic field is computed in force balance with the anisotropic pressure from the RAM code at one-hour intervals • Significantly lower plasma pressure & narrow pressure peaks are seen in the self-consistent case (bottom) compared to the dipole case (top)

  19. Self-consistent magnetic field calculations Difference between the self-consistent magnetic field and the Earth dipole field in the equatorial plane: => no significant differences on the dayside => large depressions on the nightside during the storm main phase [Zaharia et al., JGR, 2006]

  20. Self-consistent B field simulations April 22 • The self-consistently calculated ring current fluxes are significantly reduced during the main phase compared to the dipolar field calculations • The ring current morphology is approximately the same in both cases and flux peaks remain at the same local time

  21. Conclusions • We simulated the storm-time dynamics of energetic particles during 21-23 April and 21-25 October, 2001 with our kinetic RAM model. We found: • Volland-Stern model underestimated the Dst index.Weimermodel produced larger injection rate. An additional injection by radial diffusion gave the best agreement, increasing the total ring current energy by~15%near minimum Dst • The simulated ion fluxes showed pronounced ring current asymmetry during the main phase of the storm and reached maximum near local midnight in agreement with measured HENA fluxes during April 2001 • The convection models reproduced the enhancement of ~30-80 keV fluxes near dusk (dawn) seen in NOAAion (electron) data during October 2001, the ion enhancement with Weimer model was faster and stronger • The comparison with Cluster/CIS in-situ data showed good overall agreement with both models at large L. Volland-Stern underestimated the fluxes within the stagnation dip at low L; adding radial diffusion removed the sharp gradients and reduced the dips • The electron contribution to the ring current was highly variable, being negligible during quiet times and ~10% near Dst minima • Magnetically self-consistent calculations indicated deep depressions of the magnetic field on the nightside and reduced ion fluxes; their morphology, however remained unchanged

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