Substorm Current Wedge from ground magnetic observations.

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Substorm Current Wedge from ground magnetic
observations.
S.V. Apatenkov, V.A. Sergeev, (St. Petersburg
State University, Russia)thanks to E. Donovan
(UCalgary) and N.A. Tsyganenko, A. Nikolaev
(SPbU)
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Substorm current wedge.
Closure of the cross-tail current via the
ionosphere

• Motivation
• Obtain the region of a substorm
  development(relative s/c locations, phenomena
  locations, auroral features etc)
• Evaluate and take into account SCW contribution
  to magnetospheric magnetic field.

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Substorm current wedge. CS models.
Initial modelHorning, McPherron, Jackson
(1974) some improvements and algorithm
development by Sergeev et al (1989..96) 3
current systems DR, DRP, SCW idea observe at
midlatidutes, move aside of complicated auroral
current systems
Improvement details a) dipole -gt IGRF field
linesb) FACs distributed in longitudec) ring
current line -gt T89 d) 2 AEJ closure for DRP
(eastwardwestward)e) AEJ is along constant
CGLat66 instead of GLat (possible to correct
latitude if auroral observations available)
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Available observations.
INTERMAGNET, IMAGE, SAMNET, THEMIS and other ?
good longitudinal coverage around the globe!!
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Substorm current wedge. Inverse problem.
Magnetic disturbance at station k and component t
(H,D, not Z)
Up to 11 free parameters(3 amplitudes - linear)
Standard deviation
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Inverse problem. Algorithm.
A. Separate search of linear and non-linear
parametersB. Possible to look for either SCWDR
(2 CS)
or SCWDRPDR (3CS) Solve inverse
problem(1a) Direct search (step SCW5,5
DRP15,15 deg) OR (1b) Zero
assumption manually THEN(2) Downhill
simplex method (amoeba)
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Substorm current wedge. Examples.
Idealized magnetic disturbance observed along
constant latitude
Real observationsand modeled magnetic disturbance
A) Way to represent/visualize magnetic data?H,
?D versus LT or CGLongitudeB) This
representation helps to make zero approach on SCW
location
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Magnetograms, examples 2007/12/27 2008/02/02
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Results SCW vs UT, 2007/12/27
Two subsequent substorms develop in different
(although close) MLT sectors
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Results SCW vs UT, 2008/02/02
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Results SCW vs UT, 2008/02/26 2008/02/19
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IDL tool (GUI)
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IDL tool (GUI)
1) Use or not? 2) Draw m-gramm or not?
3) Data is available?
DO NOT use close to AEJ!
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backup slides
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Some typical problems and ways to solve

• Fukushima theorem. (AEJ and vortex)We are to
  remember we work with equivalent currents, since
  one observes (at the ground) magnetic disturbance
  caused by source-free ionospheric currents (Hall
  currents in case of uniform conductance)
• Induction currents. (AEJ, vortex, SCW)
• Earth is a conductor with non-uniform
  conductivity induced currents affect BX,Y and
  BZ in different way. Ways to solve(a) take into
  account induced currents situating
  superconductive sphere at some depth (depends on
  region and on variation time-scale)(b) use only
  BX and BY (increase 1.5-2) without BZ (decrease
  0.5-0.7 close to noise level)
• SQ variation. (SCW)Necessary to know for every
  midlatitude station. To be subtracted when
  investigating SCW dynamics at gt1 hour.
• Baseline. (AEJ, vortex, SCW) Visual inspection
  is required for every case.
• Not so bad! Seem to be easier and more
  reliable than e.g. spacecraft plasma instruments
  calibration

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?????????? ?????????. IDL ??????.
Input(1) INTERMAGNET data, IAGA-2002 format,
daily files, all stationshon20070323d.min
(definitive)hon20070323v.min (preliminary)(2)
SQ data for the particular day if
availablehon20070323sq.dat
?????????????????? ????????1) ????? ????2)
???????? ?????? ??? ????? ???3) ????????
????????????4) ????? ???????????? ???????5)
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??????????? ??????
1) ????? ???????. AE, AL ???????, ????? 200???
- 2007/12-2008/02 ?? 2) ?????????? INTERMAGNET
?????? 2007/12-2008/02 ??(preliminary - 3 days
delay later definitive) 3) ????? ????? ???????
??????? ??????? (?? ?-???????) 4) ?????
??????? ??? ??????????!5) ?????????? ??????????
SCW ?????? 2 ??????.6) ?????????? ???-??? ?
??????????? ????????? ???-??
- ?????????? ? ???????? ??????? ??????? - ???
??????? ???????????.- ???????? ????? ? ????????
??????? 30-80 ?? ????. ?????????.
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Substorm current wedge. State-of-the-art and
experience.

• Model Horning, McPherron, Jackson (1974)
• 3 current systems DR, DRP, SCWsome improvements
  by Sergeev et al (1992, 96)a) dipole -gt IGRF
  field linesb) FACs distributed in longitudec)
  ring current line -gt T89 d) 2 AEJ closure for
  DRP (eastwardwestward)e) AEJ is along constant
  CGLat66 instead of GLat (possible to correct
  latitude if auroral observations available)

Observations midlatitude observatories 20-55
CGLata) lt55 to avoid influence of complicated
auroral currentsb) gt20 to avoid SQ variation
influence
Contributions from SCW portions
(AEJFACsMsphC)AEJ 10-20MsphC 10FACs
70-801..3Re FAC 70 of total FAC
Other models Cramoysan et al (1995)() variable
AEJ latitude(-) always need auroral data 1
current system - SCW A tool available on web
www.dcs.lancs.ac.uk - no inverse problem only
MAG data representation.
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??????????? ??????
?????? ? ????????? ?? \\ SCW \ D \ work \ scw
??????????? ?? geo.phys.spbu.ru/themis/
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Available observations 2.
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Available observations 3.
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Planned to do
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How to use MAG_SCW (idl project)