Geoscience Reference
In-Depth Information
approximate these interactions to the first order by considering:
•
Photoionization and electron impact ionization of heavy neutrals (water
molecules).
•
Photoionization of light neutrals (atomic hydrogen).
•
Recombination of heavy ions (water ions).
•
Recombination of light ions (protons).
•
Dual elastic collisions between neutrals, ion, and electrons.
•
Coulomb interaction between ion and electrons.
•
Electronic, vibrational, and rotational cooling of electrons by water
vapor.
•
Coupling with the magnetic field.
Table 1 summarizes these interactions and shows how they are
implanted into the CASIM3D code. In these interactions, we assume that
the newly created neutrals, ions, or electrons will instantaneously accommo-
date, respectively, in the neutral, ion, or electron fluid. The balance between
ionization and recombination leads to a “mass-loading” phenomenon, where
the cometary ions are picked-up and loaded into the solar wind plasma. The
mutual friction between the fluids does not act as a net “mass loading”
term. Nonetheless, it acts in shaping the cometary coma through a strong
inter-fluid momentum and energy exchange.
Ionization and recombination rates and collisional processes are mod-
eled using the literature models and values. We based our work on the
Table 1.
Chemical and physical interactions included in CASIM3D.
Neutral fluid
Ion fluid
Electron fluid
Thermal, and
H
2
O
+
suprathermal
H
2
OH
3
O
+
H
+
Interaction
electrons
References
Photoionization
5and6
Impact ionization
7
8
Elastic and inelastic 9, 10 and 11
collisions
Electronic, vibrational,
Recombination
12
rotational cooling,
or heating
Note
:() Designates a mass, energy or momentum loss term, () a gain term, and ()
a loss or gain term.
