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Evolution of a solar wind discontinuity through its interactions with the bow
shockK. Keika (1), R. Nakamura (1), W. Baumjohann (1), W. Magnes (1),
K. H. Glassmeier (2), H. U. Auster (2), K. H. Fornaçon (2), D. G. Sibeck (3), V. Angelopoulos (4), E. A. Lucek (5), C. Carr (5), I. Dandouras (6)
(1)Space Research Institute, Austrian Academy of Sciences, Graz, Austria
([email protected] / Fax: +43-316-4120-590 / Phone: +43-316-4120-595),
(2) Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Germany,
(3) Goddard Space Flight Center, NASA, MD, USA,
(4) Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA, USA,
(5) Imperial College, London, UK,
(6) Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, Toulouse, France.
2IWF/ÖAW GRAZ
Discontinuity-bow shock interactions
June 21, 2007
A discontinuity arrived at Wind and ACE near 0910 UT.
Cluster
DSP/TC1
THEMIS
A E C B
1 3 2
3IWF/ÖAW GRAZ
Discontinuity-bow shock interactions
All S/C except THB observed a Bz increase in the discontinuity; the amplitude is >50 nT.
Rise time depends on the distance from the bow shock (BS). It is longer near BS than away from BS.
THB crossed the magnetopause into the magnetosphere at 1019 UT.
We estimate the normal direction and speed at the points indicated by three dashed lines: “Leading Edge”, “Internal Part”, and “Trailing Edge”.
THEMIS, Cluster, TC1
4IWF/ÖAW GRAZ
Discontinuity-bow shock interactions
“Internal Part” is slower than “Leading Edge” and “Trailing Edge”, even though they flow upstream with the same speed.
We suggest that bow shock sunward motion (caused by the Pd decrease) is responsible for the speed difference.
Supported by plasma flow data from both THEMIS and Cluster.
Supported by a simple calculation of Rankine-Hugoniot conditions.
BS
IP
TE
LE
x
tInterpretation
Spacecraft Part (˚)
vn (km/s)
THEMIS A, C, E
Leading -163 93
Internal -93 2.5
Trailing -116 21
Cluster 1, 2, 3 Leading 112 147
Internal 123 16
Trailing 130 108
5IWF/ÖAW GRAZ
Discontinuity-bow shock interactions
n decreased more gradually than in the solar wind.
n started to decrease before the discontinuity arrived. => implying that rarefaction waves carry the density.
|vx| decreased in the
discontinuity, at minimum around “Internal Part”.
All spacecraft saw similar profiles.
THEMIS particle data
TH
ATH
ETH
CTH
B
6IWF/ÖAW GRAZ
Discontinuity-bow shock interactions
n decreased more gradually than in the solar wind.
n started to decrease before the discontinuity arrived. => implying that rarefaction waves carry the density.
|vx| decreased in the
discontinuity, at minimum around “Internal Part”.
All spacecraft saw similar profiles.
Cluster particle data
Clu
ster
1C
lust
er
3
7IWF/ÖAW GRAZ
Calculation of RH condition
For the density-decrease event, flow in the discontinuity becomes slower than that in both sides.
Effect of BS motion on Vsw in the magnetosheathU
pst
ream
condit
ions
(fro
m W
ind o
bse
rvati
ons)
Downstream
V1
N1
Pd1
Pmag1
Pth1
VBS
V2
8IWF/ÖAW GRAZ
Summary
Discontinuity observed in SW by WIND/ACE and in the magnetosheath by THEMIS/CLUSTER
Rise time decreases during propagation in Magnetosheath
=> Change of the internal structure
Internal part slower than edge
Outward motion of BS might be responsible for lag
Interactions between a solar wind discontinuity
and the Earth’s bow shockK. Keika (1), R. Nakamura (1), W. Baumjohann (1), W. Magnes (1),
K. H. Glassmeier (2), H. U. Auster (2), K. H. Fornaçon (2), D. G. Sibeck (3),
V. Angelopoulos (4), E. A. Lucek (5), C. Carr (5), I. Dandouras (6)
(1)Space Research Institute, Austrian Academy of Sciences, Graz, Austria
([email protected] / Fax: +43-316-4120-590 / Phone: +43-316-4120-595),
(2) Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Germany,
(3) Goddard Space Flight Center, NASA, MD, USA,
(4) Institute of Geophysics and Planetary Physics, University of California Los Angels, Los Angels, CA, USA,
(5) Imperial College, London, UK,
(6) Centre d'Etude Spatiale des Rayonnements, CNRS/UPS, Toulouse, France.
10IWF/ÖAW GRAZ
This StudyBx By Bz
We examine interactions between solar wind tangential discontinuities and the Earth’s bow shock, using:
THEMIS in the duskside magnetosheath,
Cluster in the dawnside magnetosheath,
DSP/TC1 in the magnetosheath around noon.
Such a large number of spacecraft enables us
to determine propagation normal and speed of transmitted discontinuities.
to study their evolution in the magnetosheath.
Two discontinuities were observed by Wind and ACE on June 21, 2007.
11IWF/ÖAW GRAZ
Event 1: Density Increase - 1
Wind observations
By changed from -8 nT to -2 nT.
Bz increased from 3 nT to 7 nT.
|B| decreased from 10 nT to 7 nT.
N increased by a factor of ~1.5.
Vx remains almost constant.
Pd increased by a factor of ~1.5.
Pth increased by a factor of ~1.5.
Pmag decreased by a factor of ~2.
ACE observations
By changed from -10 nT to -5 nT.
Bz increased from 0 nT to 3 nT.
|B| decreased from ~10 nT to 4 nT.
Normal direction is estimated to be ~ 175˚ - 180˚, where is the latitude in GSM coordinates.
Solar wind observations
12IWF/ÖAW GRAZ
Event 1: Density Increase - 2
Cluster
DSP/TC1
THEMIS(A,E,and B)
Geotail
ClusterDSP/TC1
THEMIS(A,E,and B)
Spacecraft positions
13IWF/ÖAW GRAZ
Event 1: Density Increase - 3
DSP/TC1 observed a By change from -50 nT to -20 nT and a |B| decrease from 45 nT to 20 nT at 1246 UT. => Discontinuity.
A small structure can be seen ahead of the discontinuity: By decrease and |B| increase. => Fast forward shock generated at the bow shock.
Cluster observed similar structures followed by the discontinuity.
THEMIS A crossed the MP near 1246 UT and observed the discontinuity at 1250 UT.
The crossing is cased by inward motion of MP probably due to the generated fast forward shock.
Observations in the magnetosheath
14IWF/ÖAW GRAZ
Event 1: Density Increase - 4
THEMIS A observed sharp density increase at the discontinuity.
Cluster also observed the sharp density increase.
Rise time of density (20 - 40 s) is shorter than that of solar wind density (~2 min).
Rise time for density is slightly shorter than rise time for B changes.
Velocity observed by Cluster increased at the fast shock. It slightly decreased after the discontinuity front arrived.
THEMIS & Cluster plasma data
15IWF/ÖAW GRAZ
Event 1: Density Increase - 5
Spacecraft Method (˚) (˚) Ratio
TC1 MVA 180 28 2.2
MC 179 29
Cluster 1 MVA 150 7.8 5.7
MC 179 14
Cluster 2 MVA 178 2.1 10.9
MC ‑174 34
Cluster 3 MVA 176 29 2.6
MC ‑176 34
Cluster Timing -147 287
Spacecraft Method (˚) (˚) vn or ratio
TC1 MVA 170 21 16.0
CP 168 13
Cluster 1 MVA 146 ‑3.9 17.3
CP 147 -0.14
Cluster 2 MVA 144 ‑4.5 9.8
CP 141 3.6
Cluster 3 MVA 143 ‑0.84 8.9
CP 142 4.3
Cluster Timing 140 188 km/s
THEMIS A MVA ‑154 18
CP -152 17
Spacecraft Method (˚) (˚) vn or Ratio
Wind MVA 178 ‑20 8.0
CP -179 -26
ACE MVA 177 ‑19 19.9
CP 174 -28
Wind, ACE, TC1 Timing 174 410 km/s
Normal direction and speed
Discontinuity
Forward fast shock
MVA: Minimum Variance AnalysisCP: Cross Product of BTiming: Timing Analysis : longitude in GSM coordinates : latitude in GSM coordinates
16IWF/ÖAW GRAZ
Summary
Double Star TC1 in the dayside magnetosheath observed a fast shock (FS) at 1245:10 UT, 1 min before it saw the tangential discontinuity (TD). About two minutes later, it crossed the bow shock (BS).
Cluster in the dawnside magnetosheath observed FS at 1248:10 UT, ~2 min before they saw the TD.
Cluster observations revealed different propagation fronts; TD is ~30 deg. (~15 deg.) inclined toward dusk at Cluster (DSP/TC1), but FS is little tilted.
THEMIS A crossed the magnetopause into the magnetosheath at 1246:15 UT, because FS compressed the magnetosphere. It saw TD about 3.5 min later.
A planar front with the same normal as TD in the solar wind cannot explain time differences in the FS and TD observations between spacecraft.
TD; 1318 UT??
FS; 1245:10 UTTD; 1246:10 UTBS; 1248:30 UT
FS; 1248:10 UTTD; 1250:15 UT
FS; 1246:15 UTTD; 1249:40 UT
17IWF/ÖAW GRAZ
Conclusions
What was happening?
§ A little inclined TD hits BS near 1245 UT.
§ FS is generated and then propagating anti-sunward.
1. TD keeps propagating anti-sunward in the magnetosheath.
2. BS moves anti-sunward, because of an decrease in Alfven velocity in the magnetosheath.
The FS front is not a planar, because speed of FS is faster than that of TD in the solar wind.
The TD front is not a planar, because speed of TD is slower than that of TD in the solar wind.
TD becomes steeper in the magnetosheath, probably because speed of the TD final part becomes different from that of the TD front. Is this because of bow shock inward motion?
This results in short rise time (~2 min) of SIs in the magnetosphere.
The TD front seems greatly deformed near MP.
1. Both discontinuities compressed the magnetosphere; TD made the dominant contribution of sudden impulses (SIs) which have a front ~28° inclined toward dusk.
Does this cause dawn-dusk asymmetry of SIs?
18IWF/ÖAW GRAZ
Event 2: Density Decrease - 1
Wind observations
Bz increased from ~0 nT to 8 nT.
|B| increased from 7 nT to 12 nT.
N decreased by a factor of ~2.
Vx remains constant.
Pd decreased by a factor of ~2.
Pth decrased by a factor of 2.5.
Pmag increased from 0.02 nPa to 0.06 nPa.
ACE observations
Bz increased from -5 nT to 7 nT.
|B| increased from 8 nT to 12 nT.
Solar wind observations
19IWF/ÖAW GRAZ
Event 2: Density Decrease - 2
Cluster
DSP/TC1
ClusterDSP/TC1
THEMIS(A,E,and B)
Spacecraft positions
THEMIS
A E C B
1 3 2
20IWF/ÖAW GRAZ
Event 2: Density Decrease - 3
All S/C except THB observed a Bz increase in the discontinuity; the amplitude is >50 nT.
Rise time depends on the distance from the bow shock (BS). It is longer near BS than away from BS.
THB crossed the magnetopause into the magnetosphere at 1019 UT.
We estimate normal direction and speed at the points indicated by three dashed lines: “Leading Edge”, “Internal Part”, and “Trailing Edge”.
THEMIS, Cluster, TC1
21IWF/ÖAW GRAZ
Event 2: Density Decrease - 4
n decreased more gradually than in the solar wind.
n started to decrease before the discontinuity arrived. => implying that rarefaction waves carry the density.
|vx| decreased in the
discontinuity, at minimum around “Internal Part”.
All spacecraft saw similar profiles.
THEMIS particle data
22IWF/ÖAW GRAZ
Event 2: Density Decrease - 5
n decreased more gradually than in the solar wind.
n started to decrease before the discontinuity arrived. => implying that rarefaction waves carry the density.
|vx| decreased in the
discontinuity, at minimum around “Internal Part”.
All spacecraft saw similar profiles.
Cluster particle data
23IWF/ÖAW GRAZ
Event 2: Density Decrease - 6
Spacecraft Method (˚)
(˚) vn or ratio
Wind, ACE, TC1 Timing 170 395 km/s
Wind MVA 171 11 5.8
CP 158 13
ACE MVA 174 6.2 11.0
CP 165 5.5
Spacecraft Part (˚)
vn (km/s)
THEMIS A, C, E Leading -163 93
Internal -93 2.5
Trailing -116 21
Cluster 1, 2, 3 Leading 112 147
Internal 123 16
Trailing 130 108
Spacecraft Method (˚) (˚) Ratio
THEMIS E MVA ‑141 17 12.6
CP ‑156 17
THEMIS C MVA ‑137 9.1 4.0
CP ‑154 16
Cluster 1 MVA 114 6.7 7.4
CP 132 7.7
Cluster 3 MVA 124 13 3.2
CP 129 5.9
Cluster 2 MVA 144 9.7 2.8
CP 128 6.8
Normal direction and speed
Discontinuity
MVA: Minimum Variance AnalysisCP: Cross Product of BTiming: Timing Analysis
Discontinuity (each part)
Solar wind
24IWF/ÖAW GRAZ
Summary
Double Star TC1 in the dayside magnetosheath observed TD at 1009:40 UT, and crossed BS almost at the same time of the arrival of the TD final part.
THEMIS A, E, and C on the dusk side observed the TD front before they crossed BS. THEMIS E saw the TD front in the magnetosheath before it crossed MP.
The TD fall time is ~14 minutes.
Cluster SC observed TD in the dawnside magnetosheath.
The TD fall time is ~10 minutes.
THEMIS and Cluster observations showed that the transient region of TD has speed slower than plasma ahead of and behind it. This is probably because of bow-shock anti-sunward motion.
TD_front; 1009:40 UTTD_final; ~1016-17 UTBS; 1016:20 UT
TD_front; 1014:00 UTTD_final; 1024:00 UT
THATD_front; 1010:15 UTTD_final; 1021:10 UTBS; 1014:15 UT
THETD_front; 1010:40 UTTD_final; 1024:00 UTBS; 1011:40 UT
THBTD_front; 1011:40 UT
25IWF/ÖAW GRAZ
“Internal Part” is slower than “Leading Edge” and “Trailing Edge”.
This difference results in different rise time among spacecraft.
Supported by plasma flow data from both THEMIS and Cluster.
Supported by a simple calculation of Rankine-Hugoniot conditions.
Discontinuity-bow shock interactions
BS
IP
TE
LE
x
t
THA THE THC
Spacecraft Part (˚)
vn (km/s)
THEMIS A, C, E Leading -163 93
Internal -93 2.5
Trailing -116 21
Cluster 1, 2, 3 Leading 112 147
Internal 123 16
Trailing 130 108
26IWF/ÖAW GRAZ
Calculation from RH condition
For the density-increase event, flow in the discontinuity becomes faster than that in both sides. => Density increase becomes sharper.
For the density-decrease event, flow in the discontinuity becomes slower than that in both sides. => Density increase becomes less steep. A B change becomes more drastic around the trailing edge.
Effect of BS motion on Vsw in the magnetosheathU
pst
ream
condit
ions
Downstream
28IWF/ÖAW GRAZ
Conclusions
1. A discontinuity (TD?) hits BS near 1010 UT.
2. A fast shock (FS) is not generated? or just not detectable?
3. TD keeps propagating anti-sunward in the magnetosheath.
4. BS moves sunward, probably because of an decrease in Alfven velocity in the solar wind.
5. It is likely that the BS sunward motion causes a decrease in the speed of plasma inside TD.
• TO DO…
• Estimates of the direction and speed of boundary normals
• Check if Rankine-Hugoniot equations are satisfied.
• Compare with moeling.
TD
BS
TD
BS
TD
BS
TD
BS
29IWF/ÖAW GRAZ
Comparison We are going to make
comparison between TD with a density increase and TD with a density decrease, paying much attention to:
Whether or not FS is excited at the bow shock,
Propagation direction of FS and BS in the magnetosheath,
Variations of rise (fall) time and its relation with bow shock motion,
Rise time of geomagnetic H-component at Kakioka:
At 1245 UT; ~2 min.
At 1010 UT; ~10 min.
and magnetospheric response.
TD
BS
TD
BS
TD
BS
TD
BS
TD
BS
TD
BS
FSTD
BS
FS
TD
BS
FS