Cutting-Edge Results from Formation Flying Observations

Cutting-Edge Results from Formation Flying Observations

near Earth’s magnetopause

Hiroshi Hasegawa （長谷川 洋）

ISAS/JAXA

Meeting on “Opportunity for Collaboration on ERG and SCOPE Missions & Community Input” (16-17 March 2009)

We hope to reach a complete understanding of fundamental physical processes (reconnection, shock, & turbulence) in the Plasma Universe.

• How does it start?

• How does it evolve?

• What feedbacks/consequences does it bring about?

In the future SCOPE era

As data analysts or theorists,

We should prepare well enough for the future missions,

by learning from “currently” available data from on-going multi-satellite missions.

We should not just wait

>10 satellites in near-Earth space

Geotail

Cluster (4 sc)

THEMIS (5 sc)

KAGUYA, & SW monitor

Most of the data are publicly available.

• How does it start?

• How does it evolve?

• What feedbacks/consequences does it bring about?

As a demonstration,

Here we address the Kelvin-Helmholtz instability (KHI) that can be excited at the magnetopause (it = KHI).

What we can do with available data

Shocked solar wind

Magnetopause KHI

Hasegawa et al., 2004; Nakamura et al., 2004

Kelvin-Helmholtz vortices may play a role in transport of solar wind into the magnetosphere, in other words, anomalous transport of collision-less plasma.

• How does it start?

• How does it evolve?

• What feedbacks/consequences does it bring about?

What we can do with available data

C1 electron

C1 ion

density

Cluster event on 20 Nov 2001 (19 LT)(Hasegawa et al., 2004; Chaston et al., 2007; Foullon et al., 2008)

temperature

velocity

magnetic field

TotalPvv

)(

Total-P perturbation in the vortex

streamline

Force balance

Total-P perturbation in the vortex

• Dominant-mode period ~200 s (Wavelength ~6 Re)• Power also at ~400 s: Beginning of vortex pairing?

• Spatial initial value problem• Assumptions: MHD, d/dt =0, 2D, & B along invariant axis z.

Dominant-mode wavelength ~6 Re

Vortex structurefrom Grad-Shafranov-like reconstruction of

streamlines (Sonnerup et al., 2006; Hasegawa et al., 2007)

C1

C3

• Two vortices within one dominant-mode wavelength.

Breakup of a parent MHD-scale vortex (cascade)?

The KHI seen by Cluster was fully in a nonlinear phase, characterized by merging/breakup (inverse-cascade/cascade) of the vortices.

• How does it start?

• How does it evolve?

• What feedbacks/consequences does it bring about?

The observed KHI wavelength (~6 Re) is much longer than predicted by theory.

Why???

What we can do with available data

Simultaneous observations of the magnetopause at different longitudes

• Cluster @ 19 MLT (X ~ -4 Re) saw nonlinear KH wave.

• Geotail @ 15 MLT (X ~ +8 Re) saw what???

Geotail

Cluster

Fluctuation in the dayside boundary

• Magnetic fluctuations had a period similar to that of the KH waves.

Geotail Cluster

The KHI was generated by the mechanism that generated the magnetic fluctuations.

Reconnection @ the dayside boundary

0

BVV HT

B tensionCentrifugal force

Walén relation satisfied(Sonnerup et al., 1987)

Reconnection (or sheath fluctuations) generated the seed perturbations for the KHI excitation.

• Reconnection generated the B fluctuations?

• How does it start?

• How does it evolve?

• What feedbacks/consequences does it bring about?

What we can do with available data

4-satellite timing method →• Vn ~ 80 km/s• Crossing took ~3 sec.

Current Sheet thickness ~250 km= 2-3 times ion inertia length (~100 km)1 min

converging vortex flow

25 minBL

Ion-scale CSs at the edge of KH vortices

BL

Reconnection signatures in the thin CS

Bifurcated Current Sheet

Bn < 0

Outflow jet (V = 60 km/s ~ Alfven speed in sheath = 90 km/s)

Ne

BL

jM

VL

20 sec

Plasma Sheet Sheath

VL

Consistent with reconnection triggered in the thin CS at the vortex edge

closest to Earth0600 UT

1000 UT

X (sunward)

Y (dusk)

THEMIS string-of-pearls observation of a dayside boundary layer (BL) @16 MLT

8 June 2007

THEMIS obs. of a dayside BL

• Surface waves activity with 1-2 min period

• Simultaneous BL encounters by 2-4 SC, at several times.

• SC separated in Xby ~1.5 Re.

↓BL width ~0.5 Re40 min

closest to Earth

Eriksson et al., JGR, 2009

• Bipolar BN, at BL-to-sheath transitions, i.e., at the sunward-side edge of the surface wave.

Bipolar B oscillations on the surface wave

BN

80 min

streamline

B-field

streamline

Recovery of 2D MHD structureSonnerup & Teh, JGR, 2008

• Magnetic island & small vortex between two large-scale vortices

• Local reconnectionleading to the magnetic island formation

sheath side

Plasma sheet

N

T

What we can do with available data

• How does it start?

• How does it evolve?

• What feedbacks/consequences does it bring about?

Nonlinear KHI growth can lead to the formation of thin (ion inertia-length scale) current sheets and magnetic islands.

Geotail TH-BTH-C

TH-A,D,E

Cluster

An ideal satellite distribution in 2008

SummaryWith currently available satellite data,• How it starts & how it evolves can partly be

addressed for some processes/phenomena.• We can get some glimpse of what

consequences arise from it.

• Feedback & fast processes (electron dynamics, etc.) will be pursued by SCOPE.

• Prepare for the future, by analyzing data from on-going missions, or by developing & testing novel data analysis techniques.

Nakamura et al., 2004

Matsumoto & Hoshino, 2004

(Inverse-) cascade

Miura, PoP, 1997

Nakamura et al., GRL, 2006

Interpretation of THEMIS & Cluster events

• Thin current sheet can form at the edge of KH vortex where the CS is compressed, and may become subject to reconnection.

• KH-induced reconnection can lead to the flux rope formation. • Can it lead to large-scale plasma transport???

Anisotropy in ion V distribution

sheath

Plasma sheet

Perp heating: consistent with diffusive transport via KAW (Johnson & Cheng, 2001)