Magnetopause & its Boundary Layers
Reporter Review 2011-2013
Hiroshi Hasegawa
Inst. Space & Astronautical Science (ISAS), JAXAIAGA 2013 The XII-th Scientific Assembly(Merida Yucatan Mexico, 26-31 August 2013)

2013: 50th anniversary of the
discovery of Earth’s magnetopause &proposal of high-latitude reconnection
B directions|B|
Explorer-12
outbound crossing

Cahill & Amazeen (JGR63);
Heppner+ (JGR63)• |BMP| ~ 2 times thedipole value.
• Reconnection may
occur also for NBZ.

Dungey (1963)

Outline: macro to micro• Global Structure• Boundary Layers• Surface Waves/Deformations• Polar Cusp
• Magnetic Reconnection
Acronyms: MP (magnetopause), SW (solar wind),
LLBL (low-latitude boundary layer), ULF (ultra-low frequency),
KHI (Kelvin-Helmholtz instability), Q-|| (quasi-parallel),
KAW (kinetic Alfvén wave), LHDI (lower-hybrid drift instability)
ENA (energetic neutral atom), PIC (particle-in-cell)Global StructureSW dependence of MP position
P balance @MP:

Based on ~1000
dayside MP crossings• Larger SW pressure exerted on MP
for southward than for northward IMF.
• Consistent with blunter MP (largerflaring angle) for southward IMF.

Shue & Chao (JGR13)

Based on 15,089
MP crossings

f = 2 for planar MP

New 3D MP model by Wang+ (JGR13)

Non axi-symmetry depends on MA
X = -5 RE

MP radial position

High SW
MA caseIMF

Circular

IMF

Elongated

Low SW
MA caseConfirmed by Cluster observations

Difference from Shue97/98’s model MP Lavraud+ (JGR13); Lu+ (JGR13)

Dust effect on MP compression?
Probably No!

Dust velocity (km/s)

Treumann & Baumjohann (AG11)• Only nanodust can bepicked up to ~SW speed,
but its dynamic pressure is
too small to displace MP.
• Larger dust has low speed,i.e., little dynamic pressure.
Dust mass (kg)Mann & Hamrin (AG13)

Mercury’s tail MP: More cylindrical

MESSENGER
observations in orbit(Winslow+, JGR13)

Earth’s MP model (Shue+, JGR98)→
shows a larger flaring of the tail MP.

Possible interpretations:• Tail X-line closer toplanet at Mercury.
• Larger role of SW“static” pressure inshaping Mercury’s MP(Fujimoto+, SSR08).

Boundary Layers

Voyager not yet at the heliopause, butsaw a peculiar BL in the heliosheath

Lower-energy
particle count|B|

Innerheliosheath• |B| doubled across the“edge”, but...
Outersheath• No B-directional change.
(Boundary• SW particles decreased,Layer)suggestive of a plasma
depletion layer, but...
• GCR counts enhanced.

Galactic Cosmic Ray (GCR) count

Burlaga+, Krimigis+, Stone+ (Science13)

|B|

Boundary layer
at Mercury too
All encounteredmagnetospheres
appear to have a BL.

B-fielddirection• MESSENGER first flyby
for northward IMF.
• Dawnside boundary layer
with thickness ~1000 km,
comparable to MP
standoff altitude.
• Intermediate |B| value.
Anderson+ (PSS11)

Transport rate based on observations# of ions transferred acrossthe dayside MP: ~3 x 1026 /s
assuming flux tube length of~10 RE.
THEMIS
observed:
NBL ~10 /cc
BL width ~0.35 RE|VM| ~100 km/s
Li+ (JGR09)

Density@equator

This is sufficient to fill theplasma sheet with volume
50RE x 50RE x 5RE & Ni ~1
in only 3 hours.

• Dual high-latitude
reconnection can be thedominant “entry” mechanism.

Imber+ (AG07); Hasegawa (MEEP12); Shi+ (Nature Comms13)

Diffusion Coefficient

Evidence of eddy diffusion thickening
the dayside LLBL for northward IMF

Izutsu & Fujimoto(AG12)• Eddy diffusion can explain athickening dayside (prenoon)
LLBL for northward IMF.
MP ⇔ magnetosphere• Diff. coefficient decreases
with distance from MP.
See also Lin+ (PRL12) for generation & role of KAWs.

Surface Waves/Deformation

KH waves at Mercury’s MP
Sundberg+ (JGR12)
Boardsen+ (GRL10)• Large periodic |B|variations, consistent
with non-linear waves.

• Wave period: 10-40 s
MESSENGER@postnoon|B|– Suggesting MP
width ~proton gyroradius rgp (~200 km)– Much thinner thanEarth’s MP ~10*rgp

Occurrence position of KH-waves
Mercury

Only on dusk side
Sundberg+ (JGR12)

EarthMore often on
dusk side at X>0
Taylor+ (AG12)

Mostly for northward IMF
But see e.g. Hwang+ (JGR11)

Possibly higher growth rate on thedusk side is consistent with 2D PIC
simulations by Nakamura+ (PoP10)

Surface waves on Saturn’s MP

Masters+ (PSS12)• No clear dawn-dusk asymmetry inoccurrence, contrary to expectation
based on the flow shear magnitude.
• The surface waves mostly propagatetailward.
• Perturbation is somewhat larger on thedusk side.

MP surface waves driven byforeshock or Q-|| shock waves?

Postnoon
Plaschke+ (JGR13)• Data do not satisfy the KHI condition, but are consistent with
the MHD surface wave theory (Plaschke & Glassmeier, AG11).

Transient phenomena under radial
IMF can deform dayside MP

See also Dmitriev+ (JGR12)• Sheath super-magnetosonic flows (Hietala+, AG12) ortransient ion foreshock phenomena (Safrankova+, GRL12;
Hartinger+, JGR13) can deform MP & excite Pc5 ULF waves.

Polar Cusp
For some details, see JASTP 2012 special issue“Physical Process in the Cusp: Plasma Transport & Energization”

ENA imaging of the cusps←Southward IMF↓Northward IMF

Petrinec+ (JGR11)

IBEX observations
0.3 - 6 keV• Clear dipole tilt dependence,leading to north-south asymmetry.
• Emission also for northward IMF.
• Stronger emissions in regions
more favorable for reconnection.

Cusp energetic particles:Q-|| shock (remote) origin?
Trattner+ (JGR11;JASTP12);
Petrinec+ (JASTP12)>100 keV ions show
no strong correlation
with cusp diamag
cavity (CDC).

• Cusp & sheath energy spectra are similar, when connectedto Q-|| shock, consistent with the shock origin.

>37 keV Electrons

Cusp energetic particles:
Partly consistent withLocal origin?
local acceleration.

→ Energy (eV)→ DuskPositively charged particles for SBZ
Pitch angle(Walsh+, JGR11)

Light protons→ Sun

Acceleration by reconnection-driven potential difference.

Adamson+(AG12)
Nykyri+ (JGR11a,b; JASTP12)

Heavy ions

• Test particle simulations→ local acceleration up to ~50keV.
• Weak wave power at ~fic. Role of kinetic effects remain unclear.

Magnetic Reconnection

Diamag suppression of reconnection
Reconnection
possible
Reconnection
suppressed• Diamagnetic suppression ofreconnection (Swisdak+, JGR03),
first tested in solar wind (Phan+,ApJ10), has been confirmed for
MP too (Phan+, GRL13).
• At Saturn, high β sheath likely
suppresses reconnection(Masters+, GRL12).

Evidence of 3D topology of flux rope
• Field lines in MP flux ropes canhave various magnetic topologies.
• Suggest complex nature of MP
reconnection & energy transfer.

Øieroset+ (PRL11); Zhang+ (JGR12); Pu+ (GRL13)

Intense waves in reconnection layer,
but not exactly at the X line
Bz

3D PIC asymmetric reconnection

THEMIS observations
Density nEy, δBz, δn

Ey ~ 4vAB0 ~100 mV/m
• Frequency between fpc & fLH,
not exactly LHDI mode.
• No role in the reconnection
process (resistivity) itself.
Pritchett+ (JGR12); Tang+ (GRL13)

To be launched in late 2014

What’s coming next???
Multi-scale obs. by MMS, THEMIS, Cluster, Geotail• Electron diffusion/dissipation region in reconnection
finally detected?
• Fully 3D nature of flux ropes, magnetic null,separator, KH vortices revealed?
• Cross-scale coupling/feedback processes unveiled?

Stay tuned for updates!
http://mms.space.swri.edu/

Identifying magnetic nulls/separators• In-depth analysis of null
structures in the tail, basedon Cluster observations(Wendel & Adrian, JGR13).
• A new method developedfor tracing the separators(Komar+, JGR13).

Time is ripe for studyof 3D reconnection!

Komar+ (JGR13); see also Moore+ (JASTP13)