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Plasma entry in the Mercury’s magnetosphere

Plasma entry in the Mercury’s magnetosphere. S. Massetti INAF-IFSI Interplanetary Space Physics Institute, Roma - Italy. 2. 1. 4. D. B. A. C. D. C. B. A. 3. At IFSI we developed an analytical-empirical model mainly focused on the study of the dayside SW plasma entry:

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Plasma entry in the Mercury’s magnetosphere

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  1. Plasma entry in the Mercury’s magnetosphere S. Massetti INAF-IFSI Interplanetary Space Physics Institute, Roma - Italy

  2. 2 1 4 D B A C D C B A 3 At IFSI we developed an analytical-empirical model mainly focused on the study of the dayside SW plasma entry: • derived from an ad hoc modification of the Toffoletto & Hill TH93 magnetospheric model (IMF Bx interconnected) • by using the Spreiter’s gasdynamic approx to describe the ion magnetosheath key parameters (N/NSW, V/VSW and T/TSW), as a function of the SW Mach number (1), with the TSW calculated as a function of both VSW and heliocentric distance (Lopez & Freeman, 1986). • The model was checked for consistency with available Mariner 10 data (2) (fly-by III through the model). A check with new data from Messenger is in progress... • The kinetic properties of the m.sheath H+ ions crossing the m.pause and entering through the open field areas (3-4) are calculated following the Cowley & Owen approach, by means of the de Hoffman-Teller (dHT) reference frame. SERENA meeting 2009 - Mykonos

  3. Vpeak=Vmin+VA-SP  Vth VA_SP Vmin=VHTcos Vmax=Vpeak+Vth B A C D D C B A (from Lockwood, 1997) (from Massetti et al., 2007) SERENA meeting 2009 - Mykonos

  4. Monte Carlo Simulations •Simulation box (150 x 150 x 150) -4 RM < X < 2 RM -3 RM < Y < 3 RM -3 RM < Z < 3 RM by steps of 0.04 RM (~100km) • Surface impact data stored into a 180 x 360 lat/long grid (1°x1°) • Magnetosheath (N/NSW , V/VSW , T/TSW) and kinetic (VMIN , VPEAK) key parameters are computed over a 2°x2° m.pause grid, • Monte Carlo simulations are achieved by launching a number of test particles that is proportional to the H+ density at the magnetopause, with an initial speed randomly chosen within a bi-Maxwellian distribution, which take also into account Vmin , Vpeak (dHT) speeds || B. Particle tracking stops when H+ ions hit the planet or exit from the simulation box (i.e. in the tail). Z Y X SERENA meeting 2009 - Mykonos

  5. We performed numerical simulations for Mercury at both perihelion and aphelion, by using the most probable values of the Solar Wind and IMF, accordingly to the statistical analysis of Helios I end II data published by Sarantos et al. (2007) – Left panel Magnetosheath H+ temperature has been consistently computed as a function of VSW, DSW, |IMF B| (Spreiter et al., 1966), TSW and distance form the Sun (Lopez & Freeman, 1986) - Right panels TSW (x105) according to Lopez & Freeman (1986) Perihelion (VSW=350, DSW=60, |IMF|=40) from: Sarantos et al. (2007) TSH (km/s) (TSW = 2x105K) TSH / TSW Aphelion (VSW=430, DSW=32, |IMF|=20) distance from mp nose derived from Spreiter et al. (1966) SERENA meeting 2009 - Mykonos

  6. As expected, H+ entry is in general greater at perihelion due to both higher SW density and IMF intensity, which in turn implies wider open field regions Perihelion (0.29 AU) SW (60 cm-3, 350 km/s) - IMF (-34,+12,-10) nT Aphelion (0.44 AU) SW (32 cm-3, 400 km/s) - IMF (-16,+05,-05) nT log10 H+ density (cm-3) log10 H+ density (cm-3) SERENA meeting 2009 - Mykonos

  7. Perihelion (0.29 AU) SW (60 cm-3, 350 km/s) IMF (-34,+12,-10) nT Aphelion (0.44 AU) SW (32 cm-3, 400 km/s) IMF (-16,+05,-05) nT log10 H+ total flux (cm-2 s-1) log10 H+ total flux (cm-2 s-1) North North log10 H+ total flux (cm-2 s-1) log10 H+ total flux (cm-2 s-1) South South SERENA meeting 2009 - Mykonos

  8. Dayside magnetospheric regions (pure southward IMF case) SW (60 cm-3, 400 km/s) & IMF ( 0, 0, -20) nT the actual value of energy and flux depends upon the Alfvénic speed on both magnetosheath and magnetospheric side of the magnetopause, (i.e. on local B strength and ion density) H+ impacts (a.u.) CUSP LLBL/OPBL H+ energy (keV) H+ total flux (cm-2 s-1) SERENA meeting 2009 - Mykonos

  9. Non-adiabatic effects on H+ dayside precipitation top-left -  parameter mapped at the magnetoapuse(sq. root of min. field line curvature / max Larmor radius, Büchner and Zelenyi, 1989) , if  < 3 particles do not behave adiabatically bottom-left - H+ total flux at planetary surface bottom-right – same as bottom-left, but with m.sheath ions temperature reduced by a factor 4 κ adiabatic parameter TSH / 4 log10 H+ total flux (cm-2 s-1) log 10 H+ total flux (cm-2 s-1) SERENA meeting 2009 - Mykonos

  10. MMO MPO log10 H+ density (cm-3) log10 H+ density (cm-3) TOWARD AWAY PA distribution low-latitudes PA distribution high-latitudes SERENA meeting 2009 - Mykonos

  11. MMO MPO log10 H+ density (cm-3) log10 H+ density (cm-3) TOWARD AWAY Same SW/IMF conditions but with an higher m.sheath H+ temperature PA distribution low-latitudes PA distribution high-latitudes SERENA meeting 2009 - Mykonos

  12. *Low H+ Temp * *Low H+ Temp * MMO MPO log10 H+ flux (cm-2 s-1) log10 H+ flux (cm-2 s-1) TOWARD AWAY *High H+ Temp * *High H+ Temp * log10 H+ flux (cm-2 s-1) log10 H+ flux (cm-2 s-1) AWAY TOWARD

  13. MMO MPO H+ Vdown || B H+ Vdown |_ B H+ Vup || B H+ Vup |_ B * High H+ Temp * SERENA meeting 2009 - Mykonos

  14. Summary • magnetospheric open regions probably equivalent to those of the Earth, but extending over broader areas • IMF BX (pos./neg.) causes strong hemispheric asymmetries, in both the dayside (cusp areas) and the nightside (not shown here) • SW-IMF condition at perihelion / aphelion causes different dayside H+precipitation, by about an order of magnitude (log10 flux 9-9.5 / 8.5 cm-2 s-1) • SW precipitation on the dayside depends on both local B intensity and H+ thermal speed in the magnetosheath (due to non-adiabatic effects) • the H+ thermal speed profile along the magnetosheath is a critical parameter in the simulations (e.g. to estimate ion sputtering and SW @MPO and MMO) SERENA meeting 2009 - Mykonos

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