ICS9 Session 2: SUBSTORMS : ONSET, PROPAGATION

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ICS-9 Session 2SUBSTORMS ( ONSET,)
PROPAGATION EVOLUTION

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Session 2 (2522) Substorm Propagation and/or
Evolution

• Issue which seems to be closed?
• Breakup always corresponds (in spacetime) to
  tailward Alfvenic outflows (XNL reconnection?)
  /Ieda,-gt80 for ideal SC locations, Miyashita/
• Issues discussed
• BBFs/reconnection (gt11RE)
• Average location of flow reversal comes closer !
  (15-20Re, Miyashita, ..), some fast tailward
  flows are even observed at less than 15 Re.
  THEMIS timing
• Close temporal relationship BBFs--gtPi2s
  (Hsu,McPherron, Kepko)
• Flow bursts propagate from 17Re?11Re in 50
  (Shue, also previous Takada et 2007) --???
• BBFs Dipolarization at GEO orbit no one to
  one relationship. Statistics show no preference
  for ?Bzgt0 at GEO, when Geotail observes BBFs
  (Ohtani).

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• Multiple activations (3-10min) (Keika,
  Nakamura,), between multiple TCRs (Nagai),
• Dipolarization together with CS thinning
  (Nakamura,Sergeev..)
• Tailward and Earthward flow bursts are due to
  different activations(new source), not to
  continuous motion of NL/Nakamura/
• Tailward flows (NearEarth reconnection, on
  closed FL?) have not necessarily strong ground
  activity associated (Nakamura,)
• Dipolarizations/Injections (lt11Re)
• spatial coincidence with SCW /Dubyagin/
• EVxB0 for intense E-B variations (McFadden).
  However Runov finds large differences between E
  and VxB, at least during short lasting
  dipolarization observed on near Earth THEMIS S/C.
  
• Pressure increases/not bubbles?/
• Are all different and messy /Larson, others /

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• Propagation in X/Y
• EGP-like signature-spatial structure, propagate
  Earthward /Takada/
• BBFs propagate Earthward, DIP propagate Tailward
  (as pileup?) suppressing ??? /Takada/
• BBF can also propagate azimuthally
  /Angelopoulos, /
• DIP propagates at velocities 30-100km/s in the
  inner region/Jacquey/, plasmoid/TCR initiates at
  rlt10Re
• Dispersionless injection of energetic particles
  takes place in average at 8Re. propagate
  Earthward lt8Re, and tailward gt8Re /Spanswick, but
  not fixing Z/
• Boundaries of DIP and enhanced (dispersionless)
  accelerated protons are separate /Lin/
• DIP?BBF(Nakamura),TCS 9Re
• Both earthward and tailward fast flows in the
  inner region (vortex? Takada/Keiko)

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• Initial arc
• Henderson confirms Donovans results the first
  arc intensifies at the transition between dipole
  like and tail like field lines.
• Simulations by Voronkov show that the NL
  evolution of the shear ballooning can produce the
  vortices observed as the first arc evolves
• .
• Other issues
• Are there different SBS categories (BU arc
  location, etc), where do they start ?
• Near-Earth reconnection events how close
  (lt12Re??), how often, what controls??
• Timing of the activity is quite complex (space
  localizations, multiple sources and impulsive
  development) For instance A.Taillet finds a
  delay of only 1sec between fast tailward flow
  near Earth (ThE) and tail S/C (ThC)How to handle
  all this in data analysis??
• Nature of structuring ??
• Importance of electron bounces in the dynamics of
  the current sheet gt instabilities at ?be.
  (Louarn)

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Highlighted results
Auroral Brightening(BU)-ordered statistics
(Polar/Image - Geotail) Ieda et al reduce
spatial/temporal ambiguity, 90 of BU?TOutflows
(within couple min, may be before) in the
activated sector Miyashita et al (accurate to
2min) provide statistical maps of
changes, P, Vx, Bz, Ey, etc 5-30Re XNL at 15
-20 Re AB most typically lags
the XNL-reconnection,
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Problems in SBS evolution studies

• Inside ? Out onset scenarious
• or better? Dipolelike ? Taillike (Bz/Blobe as
  index)
• Can be solved with radial SC configuration
  (Themis)
• however, instead of X-problem
• ZvX-problem (configuration knowledge required!)
• In the tail How to separate effects controlled
  by X orXeq
• Ionosphere - knowledge of mapping curve is
  required
• YvX-problem - GBO configuration
• Multiplicity complexity of the objects
• Still far from understanding
• Importance of adaptive
• modeling

X Xeq
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ICS-9 PROPAGATION EVOLUTION

• What are the well-posed questions to answer?
• Is SBS started by CD or Reconnection? example
  of ill-posed question
• Reconnection is one of forms of Current
  Disruption (with very localized non-frozen-in
  region)
• Localised current blockade ? explosive XNL
  reconnection immediately (Pritchett, Coroniti
  kinetic simulations, 2003 also non-ideal MHD
  simulations by Ugai et al.) ,
• Broadly distributed anomalous diffusion hardly
  applicable to substorm onsets

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September 26, 2005 - Multi-spacecraft Study of
near-Earth Reconnection

• 3 events sudden brightenings, injections,
  dipolarizations AL 50..300nT
• Weak /northward IMF BZ, but SW flow pressure
  (8nPa) above the norm

• Stretched magnetotail configuration before the
  events CLTC2 in the 23h MLT plane
• Cluster Tc2 map to 64oCGLat , to the
  localized auroral brightenings (from IMAGE) in
  two isolated events
• Cluster made observations on closed field lines
  in the middle of thick (8Re) Cold\Dense
  plasma sheet

PS
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Illustration of synthetic approach ..

• Magnetic Reconnection is a basic process
• of explosive energization during substorms
• Can the reconnection XNL be formed in the near
  tail (lt15Re) in normal conditions ?
• Geotail view that typically MR starts at 20-30 Re
  distances (Nagai et.,1998)
• Very few previous observations of tailward
  Alfvenic outflows at lt15Re,
  e.g., during very strong CDAW-6 substorms
  (McPherron, Manka 1985)
• What are the critical tests for detecting XNL?
• Can MR be intense in thick Plasma Sheet on
  Closed Flux Tubes (at 10-15Re) ?
• Common view that only lobe reconnection can be
  very intense
• Embedded thin CS are rarely addressed in
  simulations

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Critical Signatures of Petschek-type Reconnection

• Set of critical signatures at
  single (or few) spacecraft ,
• to identify the
  reconnection outflow
• Fast Tailward plasma outflow southward
  magnetic flux , ideally observations of both
  T and E outflows
• Outflow V VA (taken in the inflow region)
• Hall-related quadrupole By - spatial
  distribution how far extend??
• Frozen-in magnetic field ( E VxB ?0 )
  (specific for Petschek reconnection, critical
  difference with anom.resistrivity-based CD
  models)
• deceleration of incoming electrons crossing the
  separatrix.
• ionospheric signature accelerated
  particlespoleward expansion

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Dec.16, 2006
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Substorm Dipolarizations

• A guess - Common scenario explaining variable
  magnetotail behavior during convection, SBS,
  SMC/CB and plasma injections into the inner
  magnetosphere entropy conservation-based
  scenario in the critical closed FL region (plasma
  sheet)
• S ? pV? ? const in closed convecting plasma
  tube (V? ds/B , needs MagnModel to
  probe)
• Radial distribution S(r) controls the global
  mode, e.g. HauWolf 1989,Erickson 1992 (needs SC
  constellation or perfect model to probe)
• Flat S(r)const ? steady PS convection (SMC)
• Steep S(r) profile ? energy loading (pressure
  crises) leading to SUBSTORM
• Cross-tail (radial) distribution S(y) controls
  narrow plasma streams (interchange motions,
  bubbles ? BBFs)
• Plasma bubble is able to propagate earthward
  final distance depends on its S (inward
  injections)