Plasma in the Heliosheath

John Richardson

M.I.T.

Collaborators: J. Belcher,

J. Kasper, E. Stone, C. Wang

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

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).

QuickTime™ and aSorenson Video 3 decompressorare needed to see this picture.

V1 (94 AU)

84 AU

Belcher

Plasma Flow

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

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

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

V2

V1

T

N

View from SUN:R is outward

• 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

• 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

Days 242-245

• Speed drops in discrete steps as shock approaches.

• 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.

Mach number wrt thermal plasma > 1 in heliosheath

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.)

• Shock jump comparison

• Interplanetary shock (blue),

• Neptune’s bow shock (black),

• The TS (red)

• Normalized to SW upstream of the TS

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

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)

Daily Averages • VR fluctuates |Vr| = 137 km/s• VT constant 51 km/s• VN periodic -17 km/s• Transient at

2008.62

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

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

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

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

• 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

• 110-120 day period in VN, VR

(Lomb-Scargill)

• Power in VN, VRVn

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.

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?)

• 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

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

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

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

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

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