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Cluster Reveals Properties of Cold Plasma Flow

Cluster Reveals Properties of Cold Plasma Flow. May 15, 2009 Erik Engwall. Outflows from the ionosphere. Vsc ~ 20-40 V > E ion ~ 0-10 eV. Chappell et al. [1987,2000]. Outflows from the ionosphere. Chappell et al. [1987,2000]. Model. Wake formation in flowing plasmas.

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Cluster Reveals Properties of Cold Plasma Flow

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  1. Cluster Reveals Properties ofCold Plasma Flow May 15, 2009 Erik Engwall

  2. Outflows from the ionosphere Vsc ~ 20-40 V > E ion ~ 0-10 eV Chappell et al. [1987,2000]

  3. Outflows from the ionosphere Chappell et al. [1987,2000]

  4. Model Wake formation in flowing plasmas

  5. Studies of wake formation Ion density (normalized) 150 m 1 0.8 100 m 100 m 0.6 0.4 50 m 0.2 0 m 0 m 50 m 200 m 250 m 300 m 100 m 150 m (Engwall et. al, 2006) Potential [V] 150 m 100 m 50 m 0 m 0 m 50 m 200 m 250 m 300 m 100 m 150 m

  6. Model Wake field assumed to be in flow direction: Ewake = g(u,…) u Wake formation in flowing plasmas EFW & EDI EDI FGM Velocity calculation cross-validated with CIS in low-energy mode and ASPOC operating.

  7. Model Wake field assumed to be in flow direction: Ewake = g(u,…) u Wake formation in flowing plasmas EFW & EDI EDI FGM Velocity calculation cross-validated with CIS in low-energy mode and ASPOC operating. The plasma density is obtained from the spacecraft potential (Pedersen et al., 2008) The outward flux, nu//, is now given! (We cannot separate different ion species, but we see mainly H+)

  8. Statistical study 1 s/c, July - October 2001-2005, 765.000 data points

  9. Statistical study 1 s/c, July - October 2001-2005, 765.000 data points

  10. Geographical distribution

  11. Geographical distribution cm-3 (Engwall et. al, [2006], Paper V)

  12. Outflow properties

  13. Solar and magnetic activity • Clear dependence on solar radiation and geomagnetic activity • Driving solar wind parameters are • Magnitude of the magnetic field • Solar wind dynamic pressure, nmv2

  14. Comparison to previous results Cluster study Polar @ 8 RE(Su et al. [1998])

  15. Comparison to previous results (Engwall et al., 2009) • Very good agreement to previous values: • Confirms continuation of ionospheric outflows farout in the magnetotail lobes • Ionosphere supplies plasma to magnetosphere • Cold ion outflow dominates

  16. Conclusions • Powerful new method: cold plasma flows inferred from spacecraft wakes. • Cold ions dominate in large parts of the magnetosphere, both in flux and density • Cold plasma outflow constitutes a major part of the net loss from the Earth • 1026 protons/s are lost from the planet through high-latitude low-energy outflow processes. + recent results from Mars Express Cold plasmas around planetary bodies much more important than previously thought

  17. Outflows from the ionosphere Solar cycle <8 RE Cluster Satellite missions Chappell et al. [1987,2000]

  18. Previous detections in magnetotail E (eV) Acceleration makes ions visible Cold ions in plasma sheet visible due to high flow speed on Cluster (Sauvaud et al. [2001]) • Other examples: • GEOTAIL: Hirahara et al. [1996], Mukai et al. [1994] • Polar: Liemohn et al. [2005]

  19. Previous detections in magnetotail Observations of cold plasma sheet ions when Geotail in eclipse (Seki et al. [2003]). Detection of low-energy ions (<50 eV) 9 eV Cold ions in geomagnetic tail lobes (Engwall et al. [2006], Paper 3)

  20. 18 00 12 06 Cross-polar cap potential[Haaland et al., 2007] Geographical distribution cm-3

  21. Cluster Akebono DE-1 Geomagnetic activity

  22. Model for flow velocity from wake • Unmagnetized ions on wake length scale ⇨ Spurious field is in flow direction ⇨ Ewake = g(u,…) u • Frozen-in conditions apply • EDI data are good ⇨u┴= EEDI × B / B2 We get g and u//can now be obtained from the electric field components of EDI and EFW. Ewake = EEFW - EEDI = gu┴+ g u//B/B

  23. Comparing flow velocities from particle and electric field data The derived velocity from the wake (red) shows good agreement with the corrected velocity for H+ from CODIF (black). Thus, the wake method to derive flow velocity of cold plasma works and can be used in regions where ions are inaccessible to particle detectors.

  24. Measurements from SC1 and SC3 High s/c potential will shield out the plasma ions. Few ions will thus reach CIS and the density is underestimated At the same time E-field measurements differ from EDI and EFW. Why? Because of spacecraft wake.

  25. Measurements from SC4 Artificial spacecraft potential control reduces the potential to +7 V, and some of the H+ ions will become visible! Flow aligned with B, which is expected for outflows in the polar wind. The velocity of the H+ is possible to measure due to low s/c potential. (The lowest velocities are mis-sing due to the instrument low-energy cutoff.)

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