plasma in the heliosheath john richardson m.i.t. collaborators: j. belcher, j. kasper, e. stone, c....
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Plasma in the Heliosheath
John Richardson
M.I.T.
Collaborators: J. Belcher,
J. Kasper, E. Stone, C. Wang
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Outline
• The termination shock• Overview of the first year-plus of plasma
data from the heliosheath• V1 and V2 speed differences• Flow angles and the TS shape• Comparisons of the HSH and
magnetosheath plasmas and implications for TS variability
• Summary
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Asia IHY School 2007 Sticking our Head out E. Möbius UNH/SSC -3
Apropos: Sticking Our Head OutHeliosphere: pressure balance between solar wind and local interstellar medium.
Magnetized plasmas cannot mix. Boundary is the Heliopause
Shocks form in both flows, plasma moves downstream.
Solar wind is observed (IGY).
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QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.
V1 (94 AU)
84 AU
Belcher
Plasma Flow
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Heliospheric Asymmetry.
V1 enters TS foreshock regionAt 85 AU, V2 entersAt 75 AU.
Why? A LIC magnetic field at an angle to the flow can cause asymmetries.
84 AU
75 AU
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Asia IHY School 2007 Sticking our Head out E. Möbius UNH/SSC -7
Shape of the Termination Shock• TS is blunt, as evidenced by streaming
of foreshock beams at V1 and V2
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QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Simulation of sheath (Opher)
Tilted LIC magnetic field gives asymmetry
TS and HP closer in South than North.
Magnitude of asymmetry was subject of controversy
Large asymmetry implies large LIC B field.
B
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V2
V1
T
N
View from SUN:R is outward
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• HS on DOY 261, 2007
• V(R,T,N) = 157, 59, -21 km/s• N = .0041 /cc• T = 240,000 K• Heating occurs
at shock
PLS SPECTRA
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• V2 TS Overview• Speed decrease starts
82 days, 0.7 AU before TS
• Crossing clear in plasma data
• Flow deflected as expected
• Crossing was at 84 AU, 10 AU closer than at V1
• Speed decreases before shock
Asymmetry Observed: V2 crosses the TSIn Aug. 2007 at 84 AU
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Days 242-245
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• Speed drops in discrete steps as shock approaches.
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• Total H+ energy (flow + thermal)
• Discrete steps• AFTER
increased B regions
• Lose 40% of energy before TS
• After TS, only 20% of energy in thermal plasma.
• Need T(pu) of order 6-10 keV.
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Mach number wrt thermal plasma > 1 in heliosheath
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Structures of TS crossings a few hours apart are very different: there appear to be two ramps in first crossing.Shock may be reforming downstream(Burlaga et al.)
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• Shock jump comparison
• Interplanetary shock (blue),
• Neptune’s bow shock (black),
• The TS (red)
• Normalized to SW upstream of the TS
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Jupiter Saturn Uranus Neptune ICME TS
NH/NC .34 .45 0 .48 0 - .5 0
TH/TC 6.3 7.5 0 13.0 0-10 0 T 5.1e6 4.8e6 2.6e6 3.6e6 1.8e5
Uranus has H corona - perhaps creates own pickup ions?
Study of ICME sheaths may help understand this heating.
Comparison of Reflected Ions
Jupiter
ICME Termination shock
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Daily Averages• |V| ~ 150 km/s• N - decreasing;
from .002 to .0011 /cc (Avg = .0016 /cc)
Decrease in SW flux?• T decreasing (Avg =
118,000 K)
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Daily Averages • VR fluctuates |Vr| = 137 km/s• VT constant 51 km/s• VN periodic -17 km/s• Transient at
2008.62
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Model
(Pogorelov)
4 G, field in HDP, tilted 30o
from ecliptic plane
•V1 VR > V2 VR
•V1 |VN| >V2 |VT|
V1 V2
V1 -VN
V1 VT
V2
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V1 and V2 radial speeds are different
V1 LECP Speeds in the heliosheath
(Decker et al.)
V2 PLS speeds in the heliosheath
Vr
-Vt
LECP
PLS
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V1 (LECP) V2 (PLS)
VR VT VR VT VN
67±16 -42±15 138 48 -14
V V V -32º 20º -6º
V1 - V2 comparison: Velocity
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If the TS normal is not parallel to the upstream solar wind, the solar wind is deflected at the TS.
If shock deflection gives initial flow angle in HSH, then
1) For VT after TS of 25 km/s, TS angle = 10 in RT plane
2) To make average VN angle, need 5.5° angle in RN plane.
Suggests TS more blunt in T than N directions
T
N
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• Periodicities in RN and TN planes
• 110-day period
• Averages: -6º, 20º
• Amplitudes:
8º (R-N plane),
17º (T-N plane)
|V|
R-T angle
R-N angle
T-N
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• 110-120 day period in VN, VR
(Lomb-Scargill)
• Power in VN, VRVn
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How to get oscillations?
Change shock angle? (DeflectionAt TS depends on shock normal)
Waves on shock?Change in TS shape?
To make VN oscillation, need ±6º change in TS angle with a 110 day period.
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Why 110 days?
• If fast mode speed determined by pickup ions, then round trip wave time from TS to HP is ~ 110 days.
• Changes in solar wind (heliospheric current sheet tilt, polar coronal hole boundaries, MIRs?)
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• TEMPERATURE DISTRIBUTIONS
• SW - 10,000K• HSH - 100,000 K• HSH - numerous very low T spectra• Fluctuations (∆T/T) similar
in SW and HSH, but likely a coincidence.
• T(HSH) = 13 T(SW)• We look at HSH T
distributions
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Lots of scatter in T -caused by changes in TSmotion?
T depends on TS speed
Using R-H relations,if TS speed varies ±100 km/s, T changes by a factor of 5
Good upper bound (inward motion 100 km/s)
Lower bound not as good: faster outward motion orreforming shock
Need very dynamic TS
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VR (km/s)
Jup Sat Ura Nep ICME TS
35 61 42 115 140 87 114
Jup
HSH
Comparison of plasmas in magnetosheaths and the heliosheath
HSH scales largerby factor of 1000
VR less variableIn HSH
Boundary motionless important in HSH
Speeds determined by large-scale motions
VR
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Relative Standard Deviation of VR Jupiter Saturn Uranus Neptune TS V2 0.38 0.46 2.2 0.14 0.19
V1 0.58 0.35
HSH
Jup
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Relative Standard Deviation of NJupiter Saturn Uranus Neptune TS0.62 0.41 0.41 0.13 0.520.43 0.67
185 DAY 1862
1
0
N
Density variation also from small scale shock motion?
DEN similar inMSHs and HSH.
Shock speedssimilar?
Density
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Thermal speed w
Place (w)/<w>
HSH 0.41
V1 Jup 0.26
V2 Jup 0.22
V1 Sat 0.10
V2 Sat 0.14
W more variable in HSH than in MSH
√5 variation fits data
√5 variation too big
HSH
V2 JUP MSH