The mystic twins

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The mystic twins Auroras in the North and the
SouthProf. Nikolai Østgaard
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The Sun is not only white lightbut hot boiling
plasma
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The Sun affects us The Earths magnetic field
protects us almost....
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The Solar wind penetrates our magnetic shield
NASA 2003
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Auroras in the North and South when appearing
similar
Reference Sato et al., GRL 2005
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Aurora from Space
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Aurora in the two hemispheres -displaced
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An example
Interplanetary Magnetic Field
Bx
By
Bz
Clock angle
Westward bulge SH 1.1 MLT duskward of NH
Duskward BY negative !
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Interplanetary Magnetic Field controls
Clock angle
BZ lt0 and BY gt0. (a) The tension force acting
on open field lines before they reconnect in the
magnetotail(b) Superposition of IMF and
symmetric field lines gives similar effects
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Statistical distribution of auroral brightening
(substorm onset)

• 4192 substorms by IMAGE
• 2761 Northern hemisphere
• 1431 Southern hemisphere

Clock angle
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Statistical distribution, IMF to -10 Re
Conjugate imaging
Statistical
Model
Asymmetry is 5-10 times larger than model
predictions
Liou et al, 2001 found a similar tendency
Correlating with IMF By
Østgaard et al., J.Geophys. Res., 2004 Østgaard
et al., Geophys. Res. Lett., 2005 Østgaard et
al., JASTP, 2007
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Cusp and theta aurora different in the two
hemispheres
Non-conjugate theta (transpolar arcs) consistent
with IMF Bx
Østgaard et al., Geophys. Res. Lett., 2003
Asymmetry controlled by IMF By (longitude) and
Dipole tilt angle (latitude) First simultaneous
observation of cusp aurora, But only 10 min.
Østgaard et al., Geophys. Res. Lett., 2005
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Why do we need to understand this system?

• Electric currents in the ionosphere induce
  currents on the ground
• Variations in the electron density in the
  ionosphere communication/navigation

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• High-energy particles hazard to satellittes og
  astronauts
• Large plasma laboratory to understand
  fundamental physics
• AND understand our environment

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Aurora even in BergenThanks!