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MHD Simulations of the January 10-11, 1997 Magnetic Storm

Scientific visualizations provide both scientist and the general public with unprecedented view of dynamic nature of the magnetosphere. Key aspects of storm Large scale ionospheric activity coupled with density variations Large pressure pulse pushes MP inside geostationary orbit

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MHD Simulations of the January 10-11, 1997 Magnetic Storm

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  1. Scientific visualizations provide both scientist and the general public with unprecedented view of dynamic nature of the magnetosphere Key aspects of storm Large scale ionospheric activity coupled with density variations Large pressure pulse pushes MP inside geostationary orbit Acceleration of relativistic electrons by ULF waves Demise of Telstar 401 MHD Simulations of the January 10-11, 1997 Magnetic Storm Adapted from Goodrich et al. [1998]

  2. Global Distribution / Structure of Aurora Synthetic Aurora Resonant ULF waves produce pre-midnight,multi-banded aurora Satellite Observations Intense aurora occur statistically in pre-midnightsector [Newell et al., 1996] D. Pokhotelov, W. Lotko, A. Streltsov— Dartmouth College, 2000 Photograph by Jan Curtis Ground Observations Multi-band arc structure is typical

  3. PI: W. Lotko/Dartmouth Distribution, Formation & Structure of Discrete Aurora Why do discrete aurorae intensify? drift and fade? form multi-band structure? occur statistically in pre-midnight and low-conductivity regions of the ionosphere? Atkinson-Sato feedback between magnetosphere and ionosphere converts latent energy of convection into field-line resonant Alfven waves where the conductivity is low (nightside and winter ionosphere) and where Pedersen and Hall currents tend to align (typically pre-midnight). Positive feedback occurs when the Doppler frequency of a drifting, banded density structure matches the natural frequency of the resonant Alfven wave. Aurorae ignite when the magnetic field-aligned current of the Alfven wave is impeded by microturbulence near 1 RE altitude, producing a parallel electric field and a kilovolt energy boost to precipitating plasma sheet electrons. Synthetic Arcs Resonant ULF waves produce pre-midnight,multi-banded, drifting auroral arcs Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000 Satellite Observations Bright arcs occur statistically in pre-midnight sector Ground Observations Multi-bandarc structure is typical Photograph by Jan Curtis P.T. Newell et al. 1996

  4. PI: W. Lotko/Dartmouth Are Alfvénic arcs the most common type of discrete aurora? Discrete auroras intensify, drift and fade, form multi-banded structure, and occur statistically in pre-midnight and low-conductivity regions of the ionosphere. Simulated Alfvénic arcs behave similarly. Latent energy in magnetospheric convection is radiated as resonant Alfvén waves where the ionospheric conductivity is low (nightside and winter) and the N-S Pedersen and Hall currents maximize (typically pre-midnight). “Atkinson-Sato” feedback between the magnetosphere and ionosphere ensues when the Doppler frequency of N-S drifting, ionospheric density fluctuations matches the natural frequency of participating, standing Alfvén waves. The aurora ignites as the wave field-aligned current develops microturbulence near 1 RE altitude, producing a parallel potential drop and a kilovolt energy boost to precipitating plasma sheet electrons. Alfvénic Arcs Resonant ULF waves produce pre-midnight,multi-banded, N-S drifting auroral arcs Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000 Computer Simulation Satellite Observations Bright arcs occur statistically in the pre-midnight sector Ground Observations Multi-band, N-S driftingdiscretearcs are common Photograph by Jan Curtis P.T. Newell et al. 1996

  5. PI: W. Lotko/Dartmouth Are Alfvénic arcs the most common type of discrete aurora? Discrete auroras intensify, drift and fade, form multi-banded structure, and occur statistically in pre-midnight and low-conductivity regions of the ionosphere. Simulated Alfvénic arcs behave similarly. Latent energy in magnetospheric convection is radiated as resonant Alfvén waves where the ionospheric conductivity is low (nightside and winter) and the N-S Pedersen and Hall currents maximize (typically pre-midnight). “Atkinson-Sato” feedback between the magnetosphere and ionosphere ensues when the Doppler frequency of N-S drifting, ionospheric density fluctuations matches the natural frequency of coincident, standing Alfvén waves. The aurora ignites as the wave field-aligned current develops microturbulence near 1 RE altitude, producing a parallel potential drop and a kilovolt energy boost to precipitating plasma sheet electrons. AlfvénicArcs Resonant ULF waves produce pre-midnight,multi-banded, N-Sdrifting auroral arcs Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000 Computer Simulation Satellite Observations Bright arcs occur statistically in the pre-midnight sector GroundObservations Multi-banded, driftingdiscretearcs are common Photograph by Jan Curtis P.T. Newell et al. 1996

  6. KILLER ELECTRON STORMS GEM/ISTP Geomagnetic Storm Event StudyMeasured & Simulated MAGNETIC FIELDvs UT 24-26 Sep 1998 Storm Measured at GOES-8 Simulated byLyon-Fedder-Mobarry global MHD model > 2 MeV ELECTRONS vs UT Upper. Simulated fluxes – electrons energized by Lyon-Fedder-Mobarry fields Lower. Measured fluxes – electrons at GOES-8: 30 hours spanning storm main and recovery phases Adapted from S. Elkington, Dartmouth College, 2000

  7. MAGNETOSPHERIC RESONANCE AND AURORAFAST Measurements of Field Line Resonance From Lotko, Streltsov, and Carlson [1998] DATAFrom a FAST satellite pass over a 13-minute periodically reforming auroral arc imaged at Gillam. CANOPUS magnetic, optical and radar data exhibit a coincident 1.3-mHz “resonant” toroidal pulsation. The East-West magnetic field of the pulsation is evident in FAST data (panel 1). An “electrostatic shock” forms in the North-South electric field at this altitude (panel 2). Downward electron energy flux (panel 3) and upward field-aligned current (panel 4) are signatures of the arc-related inverted V precipitation structure, which is collocated with an upflowing ion beam, flanked to the north and south by downward suprathermal electron currents. MODELSynthetic data from a virtual satellite, traversing a simulated, 88 s fundamental-mode, field line resonance layer straddling a dipole L=7.5 magnetic shell. The plasma is inhomogeneous, sustains anomalous resistivity where the parallel current becomes supercritical, and admits the finite electron inertia and ion Larmor radius. The simulated, instantaneous parallel potential drop is compared with the measured electron energy flux in panel 3 where positive/negative represents the integrated downward/upward parallel electric field at the satellite.

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