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



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 

Scientific visualizations provide both scientist and the general public with unprecedented view of dynamic nature of the magnetosphere

Adapted from

Goodrich et al

. [1998]

Global Distribution / Structure of Aurora Synthetic Aurora

Resonant ULF waves produce pre- midnight, multi-banded aurora

Satellite Observations

Intense aurora occur statistically in pre- midnight sector [

Newell et al

., 1996]

Photograph by Jan Curtis

Ground Observations

Multi-band arc structure is typical

PI: W. Lotko/Dartmouth

Distribution, Formation & Structure of Discrete Aurora

Synthetic Arcs Resonant ULF waves produce pre-midnight,

multi-banded, drifting

auroral arcs 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.

Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000

Ground Observations Multi-band arc structure is typical Satellite Observations Bright arcs occur statistically in pre- midnight sector

Photograph by Jan Curtis P.T. Newell et al. 1996

PI: W. Lotko/Dartmouth

Are Alfvénic arcs the most common type of discrete aurora?

Alfvénic Arcs

Resonant ULF waves produce pre-midnight, multi-banded, N-S drifting auroral arcs 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.

Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000 Computer Simulation

Ground Observations

Multi-band, N-S

drifting discrete arcs are common

Satellite Observations

Bright arcs occur statistically in the pre-midnight sector

Photograph by Jan Curtis P.T. Newell et al. 1996

PI: W. Lotko/Dartmouth

Are Alfvénic arcs the most common type of discrete aurora?

Alfvénic Arcs Resonant ULF waves produce pre-midnight, multi-banded, N-S drifting auroral arcs

Computer Simulation

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 plasma sheet electrons.

E altitude, producing a parallel potential drop and a kilovolt energy boost to precipitating

Research by D. Pokhotelov, W. Lotko, A. Streltsov, 2000

Ground Observations Multi-banded, drifting discrete arcs are common Satellite Observations Bright arcs occur statistically in the pre-midnight sector

Photograph by Jan Curtis P.T. Newell et al. 1996

KILLER ELECTRON STORMS GEM/ISTP Geomagnetic Storm Event Study Measured & Simulated

MAGNETIC FIELD vs UT 24-26 Sep 1998 Storm

Measured at GOES-8 Simulated by Lyon-Fedder Mobarry global MHD model Title: Graphic s produc ed by IDL Creat or: IDL Vers ion 5.0 (IRIX mipseb) Prev iew : This EPS pict ure w as not s av ed w ith a preview inc luded in it.

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> 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 Title: Graphics produc ed by IDL Creator: IDL Version 5.0 (IRIX mips eb) Preview : This EPS picture w as not saved w ith a preview included in it.

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MAGNETOSPHERIC RESONANCE AND AURORA

FAST Measurements of Field Line Resonance

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From

Lotko, Streltsov, and Carlson

[1998]

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.