Space Group

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Space Group Department of Physics Umeå University
Staff Kjell Rönnmark, prof. Patrik Norqvist,
lektor Maria Hamrin, lektor Annie Reiniusson,
doktorand Jörgen Vedin, doktorand Niklas
Melander, exjobbare
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Current research topics

• Tracking down the (auroral) generator and load
  regions Maria Hamrin, Octav Marghitu
  (MPI-Garching Bucharest),
• Method development, GALS Maria Hamrin, Kjell
  Rönnmark, Jörgen Vedin.
• Numerical simulations of auroral flux
  tubes Jörgen Vedin, Kjell Rönnmark.
• Small scale density gradients, Freja Annie
  Reiniusson, Gabriella Stenberg, Patrik Norqvist,
  Kjell Rönnmark,
• Small scale density gradients, Cluster Patrik
  Norqvist, Gabriella Stenberg,
• Bonus project 1 Cluster passage of reconnection
  separatrices Maria Hamrin, Gabriella Stenberg,
  
• Bonus project 2 Calibration of IMA, Mars
  Express Niklas Melander, Maria Hamrin, Patrik
  Norqvist, Rickard Lundin,

Hamrin, Uppsala, May 2006
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Generator and load regions in the plasma sheet
(ClusterFAST)

• Earlier study on auroral generator (Cluster
  FAST).
• Now Cluster plasma sheet crossings, fall 2001.
• EJ signatures ? concentrated loads and
  generators found (CLR, CGR).
• CLR more common. Often close to the neutral
  sheet.
• CGR often in PSBL.
• Good agreement with simulations (Birn Hesse
  2005).
• Many future prospects

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GALS Gradient Analysis by Least Squares
L100kmW20km

• Method for reconstructing the (B-) field and its
  gradients at an arbitrary point in space-time by
  using multi-spacecraft observations.
• Current density from Amperes law.
• Not very sensitive to the s/c configuration.
• Comparable or better than the Curlometer.

Hamrin, Uppsala, May 2006
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• Reasonable measures of quality.

Hamrin, Uppsala, May 2006
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Numerical simulations of auroral flux tubes

• Numerical model auroral current circuit.
• Electrons both modeled as fluid and individual
  particles (?temperature).
• Driving mechanism applied generator in the
  equatorial magnetotail ? Alfvén waves propagating
  towards the ionosphere.
• Electrons are strongly heated (parallel and
  perpendicularly) in the acceleration region.
• The model explains how field-aligned potential
  drops of several kV are supported by gradients in
  the electron temperature (pressure).

Hamrin, Uppsala, May 2006
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Small scale density gradients, Freja Cluster
Dens

• Previous studies increased E in lower hybrid
  cavities.
• Now increased E and B is found on irregular
  small scale density gradients.
• More electrostatic waves (E/B bigger) on sharp
  gradients.

Grad Dens
SE
SB

• Cluster data confirms this.

SSE
SSB
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Bonus projects

• Bonus project 1 Cluster passage of the
  separatrices of a distant reconnection site.
• Bonus project 2 Calibration of IMA, Mars
  Express..

Hamrin, Uppsala, May 2006