Plasma in the Heliosheath John Richardson M I

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 V 1 and V 2 speed differences Flow angles and the TS shape Comparisons of the HSH and magnetosheath plasmas and implications for TS variability Summary

Apropos: Sticking Our Head Out Heliosphere: 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). Asia IHY School 2007 Sticking our Head out E. Möbius UNH/SSC -3

Plasma Flow V 1 (94 AU) 84 AU Belcher

Heliospheric Asymmetry. V 1 enters TS foreshock region At 85 AU, V 2 enters At 75 AU. Why? A LIC magnetic field at an angle to the flow can cause asymmetries. 84 AU 75 AU

Shape of the Termination Shock • TS is blunt, as evidenced by streaming of foreshock beams at V 1 and V 2 Asia IHY School 2007 Sticking our Head out E. Möbius UNH/SSC -7

Simulation of sheath (Opher) Tilted LIC magnetic field gives asymmetry TS and HP closer in South than North. B Magnitude of asymmetry was subject of controversy Large asymmetry implies large LIC B field.

View from SUN: R is outward V 1 N T V 2

PLS SPECTRA • 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

Asymmetry Observed: V 2 crosses the TS In Aug. 2007 at 84 AU • V 2 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 V 1 • Speed decreases before shock

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 ke. V.

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

Comparison of Reflected Ions Termination shock ICME Jupiter NH/NC Jupiter. 34 TH/TC 6. 3 7. 5 5. 1 e 6 4. 8 e 6 T Saturn. 45 Uranus 0 0 2. 6 e 6 Neptune. 48 13. 0 ICME 0 -. 5 TS 0 0 -10 0 3. 6 e 6 Uranus has H corona - perhaps creates own pickup ions? Study of ICME sheaths may help understand this heating. 1. 8 e 5

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 30 o from ecliptic plane • V 1 VR > V 2 VR • V 1 |VN| >V 2 |VT| V 1 V 2 V 1 VT V 1 -VN

V 1 and V 2 radial speeds are different LECP V 1 LECP Speeds in the heliosheath (Decker et al. ) PLS V 2 PLS speeds in the heliosheath Vr -Vt

V 1 - V 2 comparison: Velocity V 1 (LECP) VR VT 67± 16 -42± 15 V -32º V 2 (PLS) VR VT VN 138 48 -14 V V 20º -6º

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 N T

• 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, VR Vn

How to get oscillations? Change shock angle? (Deflection At 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, 000 K • 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 TS motion? 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 or reforming shock Need very dynamic TS

Comparison of plasmas in magnetosheaths and the heliosheath VR HSH scales larger by factor of 1000 VR less variable In HSH Jup Boundary motion less important in HSH Speeds determined by large-scale motions Jup 35 Sat 61 87 114 VR (km/s) Ura Nep 42 115 ICME TS 140

HSH Jup V 2 Jupiter 0. 38 V 1 0. 58 Relative Standard Deviation of VR Saturn Uranus Neptune 0. 46 2. 2 0. 14 0. 35 TS 0. 19

2 Density variation also from small scale shock motion? 185 DAY 186 Density N 1 DEN similar in MSHs and HSH. Shock speeds similar? 0 Jupiter 0. 62 0. 43 Relative Standard Deviation of N Saturn Uranus Neptune 0. 41 0. 13 0. 67 TS 0. 52

Thermal speed w Place (w)/<w> HSH 0. 41 V 1 Jup 0. 26 V 2 Jup 0. 22 V 1 Sat 0. 10 V 2 Sat 0. 14 W more variable in HSH than in MSH √ 5 variation fits data HSH V 2 JUP MSH √ 5 variation too big