Constraining Substorm Onset from Space- and Ground-Based Observations

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Constraining Substorm Onset from Space- and
Ground-Based Observations
Department of Space Climate Physics Mullard
Space Science Laboratory
A. P. Walsh1, A. N. Fazakerley1, I. J Rae2, I. R.
Mann2,, K. R. Murphy2, M. Volwerk3
1. Mullard Space Science Laboratory, University
College London, Holmbury St. Mary, Surrey, UK 2.
Department of Physics, University of Alberta,
Edmonton, Alberta, Canada 3. Space Research
Institute, Austrian Academy of Sciences, Graz,
Austria
!7th Cluster Workshop, University of Uppsala,
15th May 2009
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Introduction 2 Substorm Models
Mullard Space Science Laboratory

• With this event we probably cant work out which
  of these is right.
• Will concentrate on near-Earth features of the
  substorm, particularly the formation of the
  Substorm Current Wedge.

Sketch UCLA
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Near-Earth Observational Signatures
Mullard Space Science Laboratory

• Include, in the ionosphere
• Geomagnetic bays ( ionospheric current)
• Pi1 Pi2 pulsations
• Auroral emissions
• Include, in the magnetotail
• Dipolarisation of the magnetic field
• Formation of Substorm Current Wedge (FACs)
• Injection of energetic particles near
  geosynchronous orbit

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Mullard Space Science Laboratory
1 October 2005 Event auroral imaging from space

• IMAGE-FUV data (southern hemisph.)
• Images every 2 mins time stamp is at the end of
  the 2 min interval during which image is
  collected
• Frey list onset at 042120 (Frey Mende, 2006)
  0419-21
• Site of auroral expansion seems to be a few degs
  east first brightening at 0421-23 expansion
  starts 0423-25

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Mullard Space Science Laboratory
1 October 2005 Event ground magnetometers

• Canadian magnetometers (northern hemisphere)
• The onset of Pi1/2 pulsations can be timed and
  localised using a wavelet transform (Milling et
  al., 2007, Murphy et al., 2009).
• Experience shows that wave power arrives a few
  minutes before auroral intensification,
  co-located within 1 or 2 degrees
• Onset of Pi1/2 activity at 0416UT at GILL (Cf
  0419-21 at IMAGE)

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Mullard Space Science Laboratory
1 October 2005 Event ground magnetometers

• Experience shows that wave power arrives a few
  minutes before auroral intensification,
  co-located within 1 or 2 degrees
• Onset of Pi1/2 activity at 0416UT at GILL (Cf
  0419-21 at IMAGE)
• A Pi1/2 onset/intensification is seen centred
  between ISLL PBQ which starts no later than
  042224 (Cf 0421-23 at IMAGE)
• Locations are consistent with the two separate
  IMAGE onsets.

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Mullard Space Science Laboratory
1 October 2005 Event ground magnetometers
GILL
PBQ

• Compare magnetometer time history for GILL and
  PBQ
• GILL shows a weaker bay (weaker ionospheric
  current overhead) consistent with main substorm
  ionospheric current being located east of GILL,
  nearer PBQ, consistent with IMAGE evidence that
  the eastward event is associated with stronger
  activity

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Mullard Space Science Laboratory
1 October 2005 Event Near Earth Spacecraft

• Blue radial line represents longitude of
  Churchill Line magnetometers used here.

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Mullard Space Science Laboratory
1 October 2005 Event Near Earth Spacecraft

• GOES12 Double Star TC-2 are close to
  magnetically conjugate with the 2nd IMAGE onset,
  apparently.
• LANL90 LANL94 bracket the onset region
• LANL spacecraft see evidence of a particle
  injection initiated near TC-2 /GOES12

GSE XY positions of Near-Earth spacecraft TC-2 at
(6.0, -2.2, 1.0) RE GSE
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Mullard Space Science Laboratory
Double Star TC-2 Data

• TC-2 in Northern hemi-sphere, in plasma sheet at
  time of 2nd IMAGE onset.
• Large deflections in dBY, pulsations in dBZ and
  enhanced T / T- observed around the time of
  onset.
• (i.e. FACs and Pi1/2s)

T// / T
PA0
PA90
PA180
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Mullard Space Science Laboratory
Double Star TC-2 Data

• TC-2 in Northern hemi-sphere, in plasma sheet at
  time of 2nd IMAGE onset.
• Large deflections in dBY, pulsations in dBZ and
  enhanced T / T- observed around the time of
  onset. (i.e. FACs and Pi1/2s)
• Sees dipolarisation and more energetic electron
  population 4 mins afterwards.

T// / T
PA0
PA90
PA180
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Mullard Space Science Laboratory
IMAGE Eastern Onset
TC-2 GOES12 Data

• GOES-12 sees deflections in BY, but in the
  opposite sense to TC-2. Timing matches IMAGE
  eastern onset.
• Consistent with the spacecraft begin located
  either side of the Western FAC of the Substorm
  Current Wedge, as it formed.
• Pi1/2 pulsations at TC-2 start at same time as
  dBY deflections. (waiting for higher time
  resolution GOES data)
• GOES12 observes the dipolarisation before TC-2.
  What does this say about SCW evolution?

Earth
j (SCW)
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Mullard Space Science Laboratory
Double Star TC-2 Data

• Pi1/2 oscillations start at 042020 UT. After
  GILL, but fits with PBQ.
• A lower energy population of field-aligned
  electrons are present during Pi1/2 pulsations.
  These disappear when the dipolarisation starts.
• Earthward flow is seen with dipolarisation, but
  not as early as Pi2 waves.
• Pulsations have frequencies of 50 to 100mHz. How
  are these related to electrons, FAC appearance
  and IMAGE onset?

Par-Perp
PA0
PA90
PA180
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Conclusions
Mullard Space Science Laboratory

• Ionosphere Pi1/2 pulsations are detected on the
  ground at virtually the same time as, and at a
  location consistent with, the main auroral
  substorm onset.
• Magnetosphere Similar pulsations at TC-2 start
  at the same time as the spacecraft sees evidence
  of the appearance of FACs which we suggest are
  part of the Substorm Current Wedge.
• M-I link? Timing evidence consistent with
  suggestion that these signatures are connected
  spacecraft and ground observations magnetically
  linked? Can we use the data to investigate the
  onset of cross-tail current diversion?
• Pi1/2 origin Possibility that the spacecraft and
  ground pulsations are a signature of local plasma
  flow is not supported in this case.

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Future Work
Mullard Space Science Laboratory

• Characterise the TC-2 pulsations properly,
  compare with candidates for current disruption
• EMIC drift (e.g. Yoon et al., 2009)
• Kinetic Ballooning (e.g. Liu et al., 2008)
• What is the role of the electrons?
• Put into the wider context of the substorm
  (Cluster data Cluster was not in the central
  plasmasheet at this events onset time).

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Mullard Space Science Laboratory
LANL Energetic Particles
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Mullard Space Science Laboratory
LANL Energetic Particles
LANL94
LANL90