Cutting-Edge Results from Formation Flying Observations near Earth’s magnetopause

1. Cutting-Edge Results from Formation Flying Observations Cutting-Edge Results from Formation Flying Observationsnear 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)

2. In the future SCOPE era 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?

3. We should not just wait 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.

4. >10 satellites in near-Earth space THEMIS (5 sc) Geotail Cluster (4 sc) KAGUYA, & SW monitor Most of the data are publicly available.

5. What we can do with available data • 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).

6. Magnetopause KHI Shocked solar wind 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.

7. What we can do with available data • How does it start? • How does it evolve? • What feedbacks/consequences does it bring about?

8. Cluster event on 20 Nov 2001 (19 LT)(Hasegawa et al., 2004; Chaston et al., 2007; Foullon et al., 2008) C1 ion C1 electron density temperature velocity magnetic field

9. Total-P perturbation in the vortex streamline Force balance

10. Total-P perturbation in the vortex • Dominant-mode period ~200 s (Wavelength ~6 Re) • Power also at ~400 s: Beginning of vortex pairing?

11. Vortex structurefrom Grad-Shafranov-like reconstruction of streamlines (Sonnerup et al., 2006; Hasegawa et al., 2007) C1 The KHI seen by Cluster was fully in a nonlinear phase, characterized by merging/breakup (inverse-cascade/cascade) of the vortices. Dominant-mode wavelength ~6 Re • Spatial initial value problem • Assumptions: MHD, d/dt =0, 2D, & B along invariant axis z. C3 • Two vortices within one dominant-mode wavelength. Breakup of a parent MHD-scale vortex (cascade)?

12. What we can do with available data • 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???

13. 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

14. Fluctuation in the dayside boundary Geotail Cluster • Magnetic fluctuations had a period similar to that of the KH waves. The KHI was generated by the mechanism that generated the magnetic fluctuations.

15. Reconnection @ the dayside boundary Walén relation satisfied (Sonnerup et al., 1987) • Reconnection generated the B fluctuations? Reconnection (or sheath fluctuations) generated the seed perturbations for the KHI excitation. Centrifugal force B tension

16. What we can do with available data • How does it start? • How does it evolve? • What feedbacks/consequences does it bring about?

17. Ion-scale CSs at the edge of KH vortices 4-satellitetiming method → • Vn ~ 80 km/s •Crossing took ~3 sec. Current Sheet thickness ~250 km = 2-3 timesion inertia length (~100 km) 25 min BL converging vortex flow BL 1 min

18. Reconnection signatures in the thin CS Ne Consistent with reconnection triggered in the thin CS at the vortex edge Plasma Sheet Sheath Bn < 0 BL Bifurcated Current Sheet jM Outflow jet (DV = 60 km/s ~ Alfven speed in sheath = 90 km/s) VL 20 sec VL

19. THEMIS string-of-pearls observation of a dayside boundary layer (BL) @16 MLT 8 June 2007 closest to Earth Y (dusk) 0600 UT 1000 UT X (sunward)

20. 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 inX by ~1.5 Re. ↓ BL width~0.5 Re closest to Earth 40 min Eriksson et al., JGR, 2009

21. Bipolar B oscillations on the surface wave BN 80 min • Bipolar BN, at BL-to-sheath transitions, i.e., at the sunward-side edge of the surface wave.

22. streamline sheath side Plasma sheet Recovery of 2D MHD structure Sonnerup & Teh, JGR, 2008 • Magnetic island & small vortex between two large-scale vortices • Local reconnection leading to the magnetic island formation streamline N T B-field

23. 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.

24. An ideal satellite distribution in 2008 TH-B Geotail TH-C TH-A,D,E Cluster

25. Summary With 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.

27. (Inverse-) cascade Nakamura et al., 2004 Matsumoto & Hoshino, 2004 Miura, PoP, 1997

28. Interpretation of THEMIS & Cluster events Nakamura et al., GRL, 2006 • 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???

29. Anisotropy in ion V distribution sheath Plasma sheet Perp heating: consistent with diffusive transport via KAW (Johnson & Cheng, 2001)