Transcript Global Simulation for a Space Weather Model: Present and

Determination of the Substorm Initiation Region From a
Major Conjunction Interval of THEMIS Satellites
A T Y Lui, V Angelopoulos, S B Mende, O LeContel, H Frey,
E Donovan, D G Sibeck, W Liu, H U Auster, X Li, M Nose, and M
O Fillingim
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Outline
Conjunction of THEMIS and GOES 11 &12 satellites
Auroral activity (AU/AL indices and GBO observations)
THEMIS observations
Time history of substorm disturbances (including GOES 11&12)
Summary and Conclusions
Conjunction of satellites
–30 R E
XGSM
–30 R E
20 R E
A
B
C
D
E
GOES11
GOES12
30 R E
YGSM
 Major
conjunction of
THEMIS
satellites
along
midnight axis
on 2008 Jan
29, 07-09 UT.
 GOES 11 &
12 bracket the
MLT of
THEMIS
alignment.
AU/AL indices During Conjunction
During the conjunction interval, there were one isolated substorm
and another substorm with multiple intensifications. The three time
indicators correspond closely to onsets of substorm activity seen by
THEMIS satellites.
Satellite Projections
Ground stations and projected satellite locations at 0800 UT
60º
70º
80º
80º
18 MLT
NAQ
CMO
20 MLT
70º
INUV
B
YKC
SIM
GOES 11
BLC
60º
06 MLT
GOES 12
04 MLT
C
FCC
PBQ
A SMI E D
02 MLT
22 MLT
00 MLT
AE stations are shown in blue, THEMIS GBO stations in green, and
THEMIS satellite projections along magnetic field lines in red. The
projected satellite locations are well embedded within these stations.
Auroral Activity at Fort Smith (FSMI)
First auroral substorm
onset at ~0714 UT
starting slightly to the
east - note the relatively
undisturbed arc (no
breakup activity)
poleward of the onset
arc.
Second substorm onset
at ~0742 UT starting
slightly to the west note undisturbed arc
poleward of onset arc.
Third substorm
activity at ~0832 UT
from the west of the
station.
Auroral Activity at Fort Simpson (FSIM)
• Fort Simpson (FSIM)
is west of FSMI.
• Substorm activity
seen was similar to
that at FSMI, i.e., arc
brightening followed
by poleward
expansion at ~0714
UT and ~0742 UT
and with relatively
undisturbed
poleward arc.
• Auroral substorm
activity at the
poleward boundary
starting at ~0831 UT.
Keograms From 4 GBO
Stations
• From top to bottom are
Double oval: retreating
equatorward at FSIM 0742
but expanding poleward
at INUV & FYKN
0828
keograms from FSMI,
FSIM, Inuvik (INUV),
and Fort Yukon
(FYKN).
• INUV & FYKN are
west of and at higher
latitudes than the
former two stations.
• Onset at ~0742 UT
reached INUV &
FYKN with poleward
expansion at ~0813 UT.
•Another activation at
~0828 UT at the
poleward boundary for
INUV & FYKN.
Movie From GBO Stations
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
THEMIS B (P1)
• No dipolarization seen by
P1 at X ~ –30 Re.
• Negative Bz but no tailward
plasma flows seen near the
first substorm onset.
• P1 exited the plasma sheet
later with negative Bz and
earthward plasma flows,
implying plasma sheet
thinning after (not before)
the substorm expansion
onset in the mid-tail region.
• It remained in the tail lobe
for the rest of the interval.
THEMIS C (P2)
• Two dipolarizations
seen by P2 at X ~ –18
Re, negative Bz and no
tailward plasma flows
for first substorm onset.
• Negligible earthward
plasma flow seen prior
to the 2nd
dipolarization.
• Strong earthward
plasma flows (~500
km/s) seen prior to the
third dipolarization.
THEMIS D (P3)
• Three dipolarizations
seen by P3 at X ~ –11 Re
with time corresponding
well to ground auroral
onsets of activity.
• Weak earthward
plasma flows (<150
km/s) seen prior to the
first dipolarization.
• Negligible earthward
plasma flows (<50 km/s)
prior to the second and
third dipolarizations.
THEMIS E (P4)
• Three dipolarizations seen
by P4 at X ~ –11 Re, similar
to P3 closeby. However,
there are big differences
between P3 & P4 in
temporal profiles of Vx and
Bz during dipolarizations.
• Weak earthward plasma
flows (<100 km/s) seen
prior to the first
dipolarization.
• Tailward plasma flows
prior to 2nd dipolarization.
• Weak earthward plasma
flows (<200 km/s) prior to
the 3rd dipolarization.
THEMIS A (P5)
• Two dipolarizations
seen by P5 at X~ –8 Re,
similar to P2 at X~ –18
Re.
• Weak earthward
plasma flows (~100
km/s) seen prior to the
2nd dipolarization.
• Very weak earthward
plasma flows (<50 km/s)
seen prior to the 3rd
dipolarization.
Observations
from GOES 11
& 12 satellites
• Dipolarization most
prominent for first
substorm onset.
• GOES 12 at postmidnight observed a
larger Bz increase
than GOES 11 at
pre-midnight,
suggesting first
onset was located in
the post-midnight.
THEMIS Vix and Bz
For 0714 UT, temporal sequence: D/E => B
For 0742 UT, temporal sequence: A => D/E => C
For 0828 UT, temporal sequence: C => E => D => A
Time History of Events
 For first auroral activation (onset of an isolated
substorm), onset location was between P2 and
P3/P4 (X = –11 to –18 Re). It was closer to P3/P4
than P2 because dipolarization at P3/P4 was
simultaneous with auroral breakup whereas that
at P2 was delayed substantially.
 For the second auroral activation (onset of a
longer duration substorm), onset location was
between P5 and P3/P4 (X = –8 to –11 Re).
 For the third auroral activation (onset of
substorm intensification, not a new substorm
expansion onset), the activity onset location was
beyond P1 (X< –30 Re).
No Magnetic Reconnection on Open Field Lines
 For first and second auroral activations (onsets of two substorms),
there was a relatively undisturbed arc poleward of the onset arc.
 The substorm activity did not reach the oval’s poleward boundary.
 These two optical features from GBO observations indicate the
absence of magnetic reconnection on open field lines.
 Even though negative Bz (|Bz|<<|Bx| => southward dipping) was
seen by P2 at X= –18 Re, there was no associated tailward plasma
flow, no tailward streaming of energetic electrons, and no signature
of the quadruple By perturbation.
 P1 at X= –30 Re observed southward dipping and earthward
plasma flow later. When P1 exited the plasma sheet after substorm
onset, it did not detect tailward streaming of energetic electrons.
 These observed features from THEMIS satellites indicate there
was no signature of magnetic reconnection at the plasma sheet
boundary, consistent with the presence of an undisturbed auroral
arc at the poleward boundary of the auroral oval.
 Therefore, there was no magnetic reconnection on open field lines
at the two substorm onsets.
Summary and Conclusions
 THEMIS major conjunction: covering from X= –5 to –30 Re.
 Three auroral activations during this interval - first two are
substorm onsets and the third one is a substorm intensification.
 Not all dipolarizations are preceded by significant earthward
plasma flows, suggesting earthward plasma flows are not a
necessary condition for dipolarization.
 For the first substorm onset, negative Bz occurs at X = –18 Re (P2)
before at X= –30 Re (P1), suggesting thinning starts earthward of
P2 and then propagates to P1 (tailward going thinning wave?).
 The first substorm is initiated in the inner plasma sheet
(X = –11 to –18 Re; closer to –11 Re than –18 Re) and does not
involve magnetic reconnection on open field lines.
 The second substorm is initiated in the inner plasma sheet
(X = –8 to –11 Re) but subsequently involves substorm disturbance
initiated beyond X= –30 Re for a substorm intensification.
 These two substorms fit the substorm synthesis model.