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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.

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Presentation on theme: "MHD Simulations of the January 10-11, 1997 Magnetic Storm Scientific visualizations provide both scientist and the general public with unprecedented view."— Presentation transcript:

1 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  Acceleration of relativistic electrons by ULF waves  Demise of Telstar 401 Adapted from Goodrich et al. [1998]

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

3 PI: W. Lotko/Dartmouth Distribution, Formation & Structure of Discrete Aurora Photograph by Jan Curtis Synthetic Arcs pre-midnight, multi-banded, drifting Resonant ULF waves produce pre-midnight, multi-banded, drifting auroral arcs Ground Observations Multi-band Multi-band arc structure is typical Satellite Observations pre- midnight Bright arcs occur statistically in pre- midnight sector Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000 P.T. Newell et al 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 R E altitude, producing a parallel electric field and a kilovolt energy boost to precipitating plasma sheet electrons.

4 PI: W. Lotko/Dartmouth Are Alfvénic arcs the most common type of discrete aurora? Photograph by Jan Curtis Alfvénic Arcs pre-midnight, multi-banded, N-S drifting Resonant ULF waves produce pre-midnight, multi-banded, N-S drifting auroral arcs Ground Observations Multi-band drifting Multi-band, N-S drifting discrete arcs are common Satellite Observations pre-midnight Bright arcs occur statistically in the pre-midnight sector Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000 P.T. Newell et al 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 R E altitude, producing a parallel potential drop and a kilovolt energy boost to precipitating plasma sheet electrons. Computer Simulation

5 PI: W. Lotko/Dartmouth Are Alfvénic arcs the most common type of discrete aurora? Photograph by Jan Curtis Alfvénic Arcs pre-midnight, multi-banded drifting Resonant ULF waves produce pre-midnight, multi-banded, N-S drifting auroral arcs Ground Observations Multi-banded, drifting Multi-banded, drifting discrete arcs are common Satellite Observations pre-midnight Bright arcs occur statistically in the pre-midnight sector Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000 P.T. Newell et al 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 R E altitude, producing a parallel potential drop and a kilovolt energy boost to precipitating plasma sheet electrons. Computer Simulation

6 KILLER ELECTRON STORMS GEM/ISTP Geomagnetic Storm Event Study Measured & Simulated MAGNETIC FIELD vs UT Sep 1998 Storm Measured at GOES-8 Simulated by Lyon-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 storm main and recovery phases Adapted from S. Elkington, Dartmouth College, 2000

7 DATA From 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. MODEL Synthetic 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. MAGNETOSPHERIC RESONANCE AND AURORA FAST Measurements of Field Line Resonance From Lotko, Streltsov, and Carlson [1998]


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