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Quo vadere possumus ? - Comparing the Hermean and the Terrestrial Magnetospheres -

Quo vadere possumus ? - Comparing the Hermean and the Terrestrial Magnetospheres -. Farkas Bolyai. Karl-Heinz Glaßmeier. C. F. Gauss. The Magnetosphere as a Plasma Laboratory. Five important areas where we learned about plasma physics: collisionless shock waves wave-particle interaction

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Quo vadere possumus ? - Comparing the Hermean and the Terrestrial Magnetospheres -

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  1. Quo vadere possumus ? - Comparing the Hermean and the Terrestrial Magnetospheres - Farkas Bolyai Karl-Heinz Glaßmeier C. F. Gauss

  2. The Magnetosphere as a Plasma Laboratory • Five important areas where we learned • about plasma physics: • collisionless shock waves • wave-particle interaction • magnetic reconnection • resonant mode coupling • substorm process

  3. Adventures in Parameter Space Each magnetospheric system may be represented by a state vector in a highly dimensional parameter space: M = M ( solar wind, planetary magnetic field, atmosphere, rotation period, plasma mass soruce... )

  4. Planet Mercury Planetary radius: 2439 km Core radius: ~1829 km Mean density: 5.42 g/cm3 Rotation period: 58.64 Tage Dipole moment: 5·1019 Am2 Surface temp.: -173°; 429° Atmosphere: No Exosphere: Yes Plasmasphere: No Magnetosphere: Yes

  5. Magnetospheric Plasma Sources Surface: Yes, sputtering, Na, about 20% gyro radii comparable to system scale ! Ionosphere: No, no atmosphere Solar wind: Yes

  6. Mercury and its Magnetic Field Ness et al, 1974

  7. The Hermean Magnetosphere Slavin et al., 1997 Magnetopause distance at about 1.8 RM

  8. Solar Wind Interaction The Hermean magnetosphere seems to be very compressible Siscoe & Christopher, 1975

  9. Magnetopause and C-F Currents The jump of 24 nT and a thickness of the mp of about 125 km gives a C-F current density of 1.5·10-7 A/m2 or a total current of 1.5·105 A, which causes a surface field of about 70 nT, e.g. about 20% of the field observed ! B  24nT

  10. ULF Waves in Mercury‘s Magnetosphere 2 s oscillation Russell, 1989

  11. Time Scales in the Terrestrial and Hermean Magnetospheres

  12. Magnetopause Stability: KHI Engebretson et al., 1998

  13. Stability of the Hermean Magnetopause The problem: How to deal with finite-larmor-radius effects ? My attempt: Try to describe these using the gyro-viscosity approach My bible: Thompson, W.B., The dynamics of high temperature plasmas, Rep. Progr. Physics, 24, 363-424, 1961

  14. The Gyro-Viscosity Approach Finite Larmor radius effects are incorporated into the MHD equations via a the gyro stress tensor T:

  15. The Hermean Magnetopause and the Gyro-Viscosity Approach Magnetopause Dawn u2 = vSW u<0 u1 = 0 u2 = 0 u>0 u1 = vSW Dusk Glassmeier, 2006

  16. The Dispersion Relation growth due to shear flow growth or stabilization(!) due to gyro viscosity Glassmeier, 2006

  17. γ/Ωi γ/Ωi 2πk/rg 2πk/rg FLR-KHI: Growth Rate The KHI growth is different for dawn and dusk ! Dusk Dawn Parameters vsw = 400 km/s TP = 5·104 K B0 = 50 nT νgyro= 2.5 ·107 m2/s

  18. A Possible Kelvin-Helmholtz Instability Configuration at Mercury Dawn stable Dusk unstable

  19. The Celebrated Dungey Equations Decoupled toroidal and poloidal oscillations for axisymmetric perturbations

  20. Jim Dungey in the Hermean Magnetosphere Glassmeier, Klimushkin, Mager, 2003 MHD: η 0 Mercury: η 0 as ω ΩNa Thus coupling due to non-zero off-diagonal components

  21. ULF Waves, Reconfiguration Currents, and Energetic Particles • Solar wind buffeting causes the m‘sphere to change • continuously • This requires ULF waves carrying the reconfiguration • currents • These currents are carried by the heavy ions, i.e. Na • As the system scale is comparable to the Na gyroradius • the necessary waves will be kinetic Alfven waves • e) These carry field-parallel electric fields, able to accelerate • particles • Potential drops of about 1 keV should be expected Thus, solar wind buffeting via generation of kinetic Alfven waves may be a major mechanism to energize the Hermean plasma

  22. Substorms in the Terrestrial Magnetosphere Ionosperic closure needs an ionosphere Baumjohann & Treumann, 1995

  23. Substorms in the Hermean Magnetosphere Siscoe et al., 1975

  24. Problem: Where do the Currents Close ? In the planetary interior ? In photoelectron layer close to the surface ? In the magnetosphere itself ? I favour this later possibility !!!!!!! For details see Glassmeier (2000)

  25. Summary Mercury is not only a hot place close to the sun, but also a very interesting point in the magnetospheric parameter space. The European-Japanese BepiColombo mission will provide us with many new insights into the plasma processes in the Hermean system. Comparing the Hermean with the terrestrial magnetosphere will also provide for a better understanding of geospace.

  26. Finished

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