“Plasma-neutral gas simulations
of reconnection events
in cometary tails”
C. Konz, G. T. Birk, & H. Lesch
2004, A&A, 415, 791-802
DOI: 10.1051/0004-6361:20031695
The formation and dynamical evolution of cometary plasma
tails and magnetic boundary layers is studied by the first
numerical plasma-neutral gas simulations.
S. Tanuma
(Kwasan Observatory)
Disconnection Event
• “Intreplanetary gas. XXVIII.
Plasma tail disconnection events
in comets: Evidence for magnetic
field line reconnection at
interplanetary sector
boundaried?”, Niedner & Brandt
1987, ApJ, 223, 655
• Comet Morehouse 1908c (Yorkes
Observatory)
• (Top) 20:57 GMT, 1908 Sep 30
• (Bottom) 19:43 GMT, Oct 1
Disconnection Event (DE)
• “Intreplanetary gas. XXVIII.
Plasma tail disconnection
events in comets: Evidence
for magnetic field line
reconnection at
interplanetary sector
boundaried?”, Niedner &
Brandt 1987, ApJ, 223, 655
• 1974 Jan 21
• Comet Kohoutek
• Des were also observed at
the comet Halley 1985-86
Reconnection in cometary tail
inflow
Hot, magnetized
ambient plasma flow
Dense, cold, neutral
and slab-like comet
× Nightside
reconnection
Current sheet
Reconnection in cometary head
inflow
Hot, magnetized
ambient plasma flow
Dayside reconnection
×
Current sheet
Dense, cold, neutral
and slab-like comet
Secure boundary
Similar Simulations
• Reconnection triggered by the comet (reconnection
around the comet, magnetotail; Niednet & Brandt 1979;
Niednet, Ionson, & Brandt 1981; Niedner 1982; Ogino,
Walker, & Ashour-Adballa 1986; Niednet & Brandt
1987; Brandt & Niednet 1987; Niedner &
Schwingennschuh 1987; Ogino 1988; Brandt & Snow
2000)
• Reconnection triggered by the high velocity cloud
(Konz, Birk, & Lesch 2004; Konz, Bruns, & Birk 2002)
• Reconnection in the earth’s magnetosphere (Ogino’
papers; Birk, Lesch, & Konz 2004)
• Reconnection triggered by the flux tube
Earth
• “Solar wind induced magnetic field around
the unmagnetized Earth”, Birk, Lesch, &
Konz 2004, A&A, 420, L15 (pdf)
• See also Ogino’s papers
High Velocity Clouds
• “Dynamical evolution of
the high velocity clouds”
Konz, Birk, & Lesch 2004,
ApSS, 289, 391 (pdf)
• “Dynamical evolution of
high velocity clouds in the
intergalactic medium”,
Konz, Bruns, & Birk 2002,
A&A, 391, 713: Strong
radio emission around
HVC complex C (pdf; fig)
New point of this paper
• Two fluid (ion and plasma)
• Collisional momentum transfer
• (Birk& Otto 1996, J. Comp. Phys., 125,
513)
• Small and many grid
• Harris-like sheet
Basic Equation (1)
Plasma continuum equation
Neutral gas continuum equation
Plasma momentum equation
Neutral gas momentum equation
Normalization by L, Alfven velocity, Alfven time, magnetic pressure
Basic Equation (2)
Plasma pressure equation
Recombination/
ionization
Neutral gas pressure equation
Induction equation
Constraint of
momentum conservation
Classical model
Typical parameters
in solar wind at 1 AU
• L=5x10^10 cm (The extend of ionosphere
of comet at 1 AU)
• No=12 cc
• Bo=5x10^-3 G
• Va=3.15x10^8 cm/s
• ta=159 s
• (Typical quantities at 1 AU)
Initial Condition (Run I)
Vy0=-0.15 (=470 km/s); MA=15
Hot, magnetized
ambient plasma flow
Y=30
Rho_min=1
To=100
Y=0
R=2
B=Bx
Dense, cold, neutral
=Bo
and slab-like comet
=0.01
Rho_no=1.5x10^4
(=50microG)
(no=12 cc)
T_no=1
-60<x<60
-250<y<30
303x703 grids
Y=-250
X=-30
X=0
X=30
Anomalous resistivity model
Eta_=10^-5 (>eta_num=10^-6)
Eta_2=0.05
Jc=0.1
• They always adopt this model. They assume
a background resistivity for the first time.
B, v,
resistivity
T=2
T=1786
core
T=300
T=2372
T=900
T=2431
Anomalous resistivity sets in
Nightside reconnection
Petschek reconnection starts at t=1000
Jz
|B|
Results of Run I
• Disconnection event (DE): Solar wind magnetic
barrer; Dayside diffusion comet’s ionosphere night
side reconnection
• This process is quasi-syclic.
• Since we did not include mass-loading of the solar wind
and outgasing from the comet's surface, no plasma
density enhancement can be seen in the ejected tail.
• However, increased Ohmic dissipation at the pinched
region can account for a brightening of the disconnected
tail head.
• Including ionization processes and outgasing of neutrals
is necessary to end up with a plasmoid like density
enhancement of the tail plasma.
Initial Condition (Run II)
Harris-type current
Vy0=-0.15 (=470 km/s); MA=15
Hot, magnetized
sheet is assumed at
ambient plasma flow
y=25 at t=705ta in Y=30
Rho_min=1
Run I. The other Y=25
To=100
conditions are same
Y=0
with Run I.
R=2
Dense, cold, neutral
and slab-like comet
Rho_no=1.5x10^4
(no=12 cc)
T_no=1
B=Bx
=Bo
=0.01
(=50microG)
-60<x<60
-250<y<30
303x703 grids
Y=-250
X=-30
X=0
X=30
Strong current
Second
boundary
Run I
Run I
Results of Run II
• The dayside reconnection occurs violently.
• Dayside reconnection: more dynamic, more
violent, 2.5 times higher resistivity, higher
reconnection rate, shorter time scale
Conclusion
• The formation and dynamical evolution of cometary plasma tails and
magnetic boundary layers is studied by the first numerical plasmaneutral gas simulations.
• It is shown that collisionless interaction between the cometary
envelope and the solar wind plasma leads to the formation of a
magnetic barrier.
• The dynamics of the magnetotail are governed by multiple magnetic
reconnection.
• If the comet encounters a heliospheric current sheet, strong
disconnection events characterize the cometary plasma tail.
• But even in the case of homogeneous solar wind conditions, partial
disruption of the tail is triggered by dayside reconnection.

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