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Travel-time Magnetoseismology

Travel-time Magnetoseismology. Peter J. Chi and C. T. Russell UCLA/IGPP. Acknowledgments: MHD simulation results are provided by Dong-Hun Lee. Earth. The Scientific Question. How do the impulse-induced perturbations propagate in the magnetosphere?

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Travel-time Magnetoseismology

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  1. Travel-time Magnetoseismology Peter J. Chi and C. T. Russell UCLA/IGPP Acknowledgments: MHD simulation results are provided by Dong-Hun Lee. Peter Chi: Travel-time magnetoseismology

  2. Earth The Scientific Question • How do the impulse-induced perturbations propagate in the magnetosphere? • How can such knowledge help us estimate the state of the magnetosphere? Peter Chi: Travel-time magnetoseismology

  3. Three Seismologies, Two Methods Travel-time Normal-mode Peter Chi: Travel-time magnetoseismology

  4. Scale Lengths Associated with Magnetoseismology Scale Comparison Dayside impulses Nightside impulses Can’t use ray tracing in magnetoseismology !!! Peter Chi: Travel-time magnetoseismology

  5. Tamao’s Model of Impulse Propagation via MHD Waves Alfven Tsutomu Tamao • Compressional Mode: • Propagates in all directions • Suffers geometrical attenuation (~ 1/r) • Alfven Mode: • Propagates along magnetic field line • Wave energy conserved Compressional Tamao [1964a] “Tamao travel path” : preserves most wave energy Peter Chi: Travel-time magnetoseismology

  6. Impulse Travel Time Predicted by Tamao’s Model Peter Chi: Travel-time magnetoseismology

  7. Simulation of Sudden Impulse Propagation via MHD Waves B Alfvén speed (Simulation made by Dong-Hun Lee) Peter Chi: Travel-time magnetoseismology

  8. Currents Associated with the Compression MHD waves Ionospheric Hall current Kikuchi and Araki [1979] ? Field-aligned current Kikuchi and Araki [1979]; Kikuchi et al. [1996] Tamao [1964b] Peter Chi: Travel-time magnetoseismology

  9. B MHD simulation (Noon meridian) t onset arrival Earth Subsolar point Propagation of Impulse Front (Onset) • It is argued that the Earth-ionosphere waveguide model is evidenced by the simultaneous onset time seen on the ground across all latitudes. • Onset will be seen across all latitudes on the ground within ~10 sec (without the need of Earth-ionosphere wave guide)! Peter Chi: Travel-time magnetoseismology

  10. Propagation of Impulse Conventional (static) View Dynamics View + Tamao [1964b] Peter Chi: Travel-time magnetoseismology

  11. MHD Simulation on Ionospheric Currents due to Impulse Plasmapause Latitude Peter Chi: Travel-time magnetoseismology

  12. Tremors (quakes) in space Peter Chi: Travel-time magnetoseismology

  13. Density Model and Inversion Tamao Model of Wave Propagation Density Function (Lpp: plamapause L-value) d Nonlinear optimization e a b c (t0: start time) Parameters to solve: (t0,) nmp, m1, Lpp, npp, m2 Peter Chi: Travel-time magnetoseismology

  14. Density Profile Estimated through Magnetoseismic Inversion In situ observations by Akebono also suggest that the plasmapause Lpp ~ 3.5 prior to the SI event. Peter Chi: Travel-time magnetoseismology

  15. Polar 48.4 sec Polar’s Observation of Impulse Time • Estimated Start time: 2344:20 UT • Calculated travel time from impact location to Polar: 48.4 sec • Observed arrival time at Polar: 2345:08 UT Peter Chi: Travel-time magnetoseismology

  16. Nightside Magnetoseismology • Tamao’s travel path: • From low L to high L • From high L to low L Peter Chi: Travel-time magnetoseismology

  17. Test of Inversion: Using Artificial Data • Artificial Data: • 10 imaginary observations equally spaced between 6 and 24 in L-value (all outside the plasmasphere) • Timing uncertainty: 5 sec • Arrival time consistent with Tamao travel time • Models: • Magnetic Field: T89 • Plasma: • n = nsh/(1 – exp–L/12) • T = Tsh/(1 – 0.5 exp–L/12) Peter Chi: Travel-time magnetoseismology

  18. Polar Polar-THEMIS Joint Observations for Magnetoseismic Studies • THEMIS will deploy five satellites near the equatorial plane. • Magnetoseismic inversion can take advantage of all satellite observations, but it favors the observations distributed across different regions. • Polar can provide joint observations at high latitudes, giving critical timing records for Alfven wave propagation. (Modified from the diagram on the THEMIS web site) Peter Chi: Travel-time magnetoseismology

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