Plasma entry in the Mercury’s magnetosphere S. Massetti S. Massetti INAF-IFSI Interplanetary Space...
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Transcript of Plasma entry in the Mercury’s magnetosphere S. Massetti S. Massetti INAF-IFSI Interplanetary Space...
Plasma entry in the Mercury’s Plasma entry in the Mercury’s magnetosphere magnetosphere
S. MassettiS. Massetti
INAF-IFSI INAF-IFSI Interplanetary Space Physics Institute, Roma - ItalyInterplanetary Space Physics Institute, Roma - Italy
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.
1
2
A
BC
D
3
A B C D
4
SERENA meeting 2009 - Mykonos
SERENA meeting 2009 - Mykonos
(from Massetti et al., 2007)
A
B
C
D
Vmin=VHTcos
VA_SP Vth
Vpeak=Vmin+VA-SP
Vmax=Vpeak+Vth
A B C D
(from Lockwood, 1997)
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°x 2° 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).
Y
X
Z
SERENA meeting 2009 - Mykonos
SERENA meeting 2009 - Mykonos
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
distance from mp nose
TS
H /
TS
W
TS
H (
km/s
) (T
SW =
2x1
05K
)
Perihelion (VSW=350, DSW=60, |IMF|=40)
Aphelion (VSW=430, DSW=32, |IMF|=20)
VSW \ AU 0.29 0.36 0.44
350 1.4 1.1 0.9
400 2.1 1.7 1.4
TSW (x105) according to Lopez & Freeman (1986)
from: Sarantos et al. (2007)
derived from Spreiter et al. (1966)
SERENA meeting 2009 - Mykonos
log1
0 H+ density (cm
-3)
Aphelion (0.44 AU)SW (32 cm-3, 400 km/s) - IMF (-16,+05,-05) nT
log1
0 H+ density (cm
-3)
Perihelion (0.29 AU)SW (60 cm-3, 350 km/s) - IMF (-34,+12,-10) nT 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
SERENA meeting 2009 - Mykonos
log1
0 H+ to
tal flux (cm-2 s
-1)log
10 H
+ total flux (cm
-2 s-1)
log1
0 H+ to
tal flux (cm-2 s
-1)log
10 H
+ total flux (cm
-2 s-1)
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
North North
South South
H+ energy (keV
)H
+ imp
acts (a.u.)
H+ to
tal flux (cm-2 s
-1)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)
SERENA meeting 2009 - Mykonos
LLBL/OPBLCUSP
log1
0 H+ to
tal flux (cm-2 s
-1)
SERENA meeting 2009 - Mykonos
κ adiabatic param
eter
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
log 10 H
+ total flux (cm
-2 s-1)
TSH / 4
SERENA meeting 2009 - Mykonos
PA distribution low-latitudes PA distribution high-latitudes
log1
0 H+ density (cm
-3)
TOWARD
log1
0 H+ density (cm
-3)
AWAY
MMO
MPO
SERENA meeting 2009 - Mykonos
PA distribution low-latitudes PA distribution high-latitudes
log1
0 H+ density (cm
-3)
TOWARD
log1
0 H+ density (cm
-3)
AWAY
Same SW/IMF conditions but with an higher m.sheath H+ temperature
MMO
MPO
log1
0 H+ flu
x (cm-2 s
-1)
AWAY
log1
0 H+ flu
x (cm-2 s
-1)
TOWARD
log1
0 H+ flu
x (cm-2 s
-1)
TOWARD
log1
0 H+ flu
x (cm-2 s
-1)
AWAY
*Low H+ Temp * *Low H+ Temp *
*High H+ Temp * *High H+ Temp *
MMO
MPO
SERENA meeting 2009 - Mykonos
H+ Vdown || B H+ Vdown |_ B
H+ Vup || B H+ Vup |_ B
MMO
MPO
* High H+ Temp *
SERENA meeting 2009 - Mykonos
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)