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Tracing solar wind plasma entry into the magnetosphere using Ti/Te ratio

Beno i t Lavraud CESR/CNRS/Université de Toulouse, France and the Cluster teams “remote” contribution to the ISSI meeting of Feb. 2009. Tracing solar wind plasma entry into the magnetosphere using Ti/Te ratio. At low SW Mach number the magnetosphere behaves very differently; effects include:

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Tracing solar wind plasma entry into the magnetosphere using Ti/Te ratio

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  1. Benoit LavraudCESR/CNRS/Université de Toulouse, Franceand the Cluster teams“remote” contribution to the ISSI meeting of Feb. 2009 Tracing solar wind plasma entry into the magnetosphere using Ti/Te ratio

  2. At low SW Mach number the magnetosphere behaves very differently; effects include: • Magnetosheath βproperties • Strong/asymmetric flows in magnetosheath • Asymmetric magnetopause shape • Cross Polar Cap Potential saturation • Changes to dayside reconnection rate • Alfvén wings/Sawtooth oscillations, … •  And lower ion-to-electron temperature ratio in the magnetosheath MOTIVATION: solar wind Mach number

  3. MOTIVATION: Tracing plasma entry Because magnetosheath ion-to-electron temperatureratio is lower during low Mach number (<6), I’ve been wondering whether one might use this property to trace SW plasma entry into the magnetosphere. This presentation shows preliminary Cluster results that suggest we might indeed be able to do so…

  4. Magnetosheath flow acceleration and asymmetry Equatorial plane X = -5 RE • Asymmetric flow acceleration, along the flanks only: somewhat similar to a magnetic “slingshot” • Larger flows along flanks might enhance KH transport

  5. Observation of such magnetosheath flow jets dusk Sheath Cluster Electrons shock sheath Ions • Solar wind observations: • IMF large and north • SW density low • Cluster observations: • Flows B fieldoutside MP • Up to 1040 km/s while • SW is only 650 km/s SW speed Magnetopause  Flows not associated with reconnection and 60% > SW

  6. Cluster overview of MP/sheath during the same day KH wave activity No clear (N-Vx) roll-up Boundary layer Inside MP Large sheath flows dusk Cluster shock sheath • Solar wind observations: • Long low SW MA interval during a CME/MC • Cluster observations: • One clear instance of KH activity at MP/BL Three clear boundary layer intervals in total Magnetopause  Three clear boundary layer intervals with SW-like plasma inside the magnetopause

  7. Temperature ratio observations for this interval Ti/Te NOT conserved Ti/Te conserved  Ti/Te appears conserved for SW plasma in BL, instances where it is not conserved resemble pre-existing PS

  8. In this event, that BL contain SW plasma is obvious, although confirmed using this test as compared to inner PS plasma • Possible future implications I would seek: • - Determine which processes (reconnection, KH, else?), if any, conserve this ratio during entry • - Trace entry into inner mag. regions(time-scales) • How does this info get lost/destroyed? (drifts in inner regions, etc.) • Note: Cluster/THEMIS case around CME of Nov. 20, 2007 CONCLUSIONS

  9. EXTRA MATERIAL

  10. Magnetosheath flow dependence on Mach number Illustration of strong sheath flows from Lavraud et al. [2007] Global MHD simulations (BATS-R-US) for high and low Mach numbers • Strong flow acceleration : increasing for decreasing MA See also Chen et al. [1993], Rosenqvist et al. [2007]

  11. Movie of the field line « slingshot »

  12. Mechanism of magnetosheath flow acceleration MHD simulation for low MA • Steady state momentum equation: • Magnetic forces • Integration of forces: Selection of streamline Y (RE) ∂s Z (RE) Note:Not a simple analogy to a “slingshot”, magnetic pressure gradient as important as tension force (~10% 45% 45%)  We can estimate the contribution of each force:J x B acceleration dominates at low Mach numbers

  13. Observation of such magnetosheath flow jets dusk Sheath Cluster Electrons shock sheath Ions • Solar wind observations: • IMF large and north • SW density low • Cluster observations: • Flows B fieldoutside MP • Up to 1040 km/s while • SW is only 650 km/s SW speed Magnetopause  Flows not associated with reconnection and 60% > SW

  14. Flow asymmetry: role of IMF direction Flow magnitude and sample field lines from MHD simulations (X = -5 RE)  The enhanced flow location follows the IMF orientation+ additional anomalous flow deflections [Nishino et al., 2008]

  15. Acknowledgments Aaron J. Ridley (Univ. Michigan, USA) Janet Kozyra (Univ. Michigan, USA) Maria M. Kuznetsova and CCMC (NASA GSFC, USA) and Cluster teams

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