Plasmasheet Response to Multiple Substorm Activations

1
Plasmasheet Response to Multiple Substorm
Activations
The Interball-ground experimentators
T. Bösinger, V. A. Segeev, A. G. Yahnin, L.
Vagina, K. Kudela, J.-A. Sauvaud, D. Milling,
N. L. Borodkova, V. N. Lutsenko, A. Skalsky, et
al.
2
What?
1
A series of substorms, substorm intensifications
and activations north of Scandinavia on 9
December 1995 and Interball Tail Probe (IT1) and
its Companion (IT2)
Substorm I
Substorm II
Substorm III
Table 1 Time line, observation platforms, main
events
SCW Substorm Current wedge uFAC upward
directed Field Aligned Current AEJw westward
Auroral ElectroJet PS Plasma Sheet
3
Where?
2
IT-1
IT-2
Neutral Sheet
Interball Tail probe IT-1
Fig. 4
The IMAGE network of magnetic recordings.
4
SCW parameters
Pi2/Pi1B onsets

• no electrojet currents,
• magnetic signatures gt DP1 current system
• determination of SCW position, parameters, etc.

5
Interball tail-probe (IT-1) - ground temporal
correlation
Pi2/Pi1B onsets

• close temporal relationship between magnetic
• signatures at IT-1 and auroral stations (e.g.
  KEVO)
• from 20 to 22 UT
• 4 substorms, the first three conjugate to
  Scandinavia

6
ELECTRON data from Interball tail-probe (IT-1)

• disappearance of PS electrons (exit to the lobe)
  gradually
• starting at 1930 and in between 2043 and
  2052 UT.

• similar to above but with higher time resolution
  
• (2020 to 2100 UT) and PA close to
  field-aligned
• note behaviour of S/C potential (low energy
  electrons)

7
B-field (gsm) at IT-1
20 nT
Bz
By
Bx
lobe
SCW
-40 nT
2015 UT
2045 UT
20 nT
Bz
By
SCW
Bx
lobe
-40 nT
2030 UT
2100 UT

• large changes in Bx, small changes in By and Bz
• intrusion of IT-1 into PS gt PS expansion
• intrusion of IT-1 into PS in agreement with
  ELECTRON data
• IT-1 not far from the PS-boundary
• no or only small signatures of dipolarization
• spiky By bursts, By-shear gt FAC
• at PS-boundary FACs ?
• SCW gt large scale, large time constant current
  system
• FACs at PS-boundary gt current filaments
• current filements in B-turbulent region

8
By spikes (IT-1)
2048 UT
2052 UT
9
Electron energy spectra (IT-1)
10
Injection at Magion-4 (IT-2)
T1
T4
T2

• T1 202242 UT
• T2 204830 UT
• T4 205100 UT

11
Timing PS-expansion (IT-1) versus Injection
(IT-2)
The high temporal resolution of PRAM, ELECTRON
(IT-1) and DOK-S (IT-2) data made it possible to
do some relative timing analysis

• throughout the timing analysis we distinguished
  between onset
• and peak values, wherever possible.
• during substorm I, the appearance of
  PS-electrons at IT-1
• occurred within 3 s at the same time,
  independent of energy
• and pitch-angle.
• the same holds for substorm II within 6 s,
  beside that PS
• electrons appeared in 3 subsequent jumps. Each
  was dealt
• separately.
• during substorm II, the onsets of sudden Bx
  deflection and
• PS-electrons appearance (IT-1) were delayed by
  10 to 20 s with
• respect to electron injection onset (IT-2). The
  peak values in the
• 3 data sets were, however, reached
  simultaneously.
• during substorm I, the onsets of Bx deflection,
  and appearance
• of PS-electrons (IT-1), and electron injection
  signatures (IT-2)
• were probably also delayed (data gap).
• Pi2/PiB onsets as determined on the ground were
  within 1 min
• simultaneous with IT-1/IT-2 signatures.
• the By spike associated appearance of PS
  electrons was lead by
• field-aligned electrons.

12
Summary and Conclusions
general aspects

• substorms during low magnetic activity
• substorms of small intensity (lt 100 nT)
• practically no PEJ currents
• magnetic signatures only of DP-1 type
• active region north of Scandinavia
• contracted auroral oval
• no injection signatures at geostationary orbit
• IT-1 and IT-2 conjugate to active region at x
  -10-12 Re
• IT-1 and IT-2 either inside PS, close to NS, at
  PS boundary
• or exiting into the lobe
• PS expansion simultaneous with onsets of
  substorms,
• no or small dipolarization signatures
• appearance of PS electrons at IT-1 simultaneous
  within
• 3 s regardless of energy and pitch angle
• injection signatures (gt 23 keV) at IT-2 (-10.6
  Re) 10-20 s
• earlier than PS expansion at IT-1 (-11.6 Re)
• IT-1 and IT-2 close but tailward of reconnection
  region
• tiny, small substorms exhibit the same
  signatures as big
• ones

13
Summary and Conclusions
specific aspects

• field-aligned current filements (By spikes) at
  PS boundary
• during PS expansion
• appearance of By spike associated PS electrons
  led by
• field-aligned electrons
• deeper in the PS, electrons PA distribution
  isotropic
• deeper in the PS, B-field turbulent
• B-field turbulence as long as SCW development