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Table 1
Constant physical and simulation parameters for Runs 1–4.
| Quantity | Symbol | Expression | Unit | Reference |
|---|---|---|---|---|
| Heliocentric distance | d⊙ | 1.425 | AU | |
| Upstream solar wind and IMF | ||||
| Solar wind proton bulk speed |  |
430 | km s−1 | Slavin & Holzer (1981) |
| Solar wind proton density |  |
3.45 × 106 | m−3 | Slavin & Holzer (1981) |
| Proton temperature |  |
63 200 | K | Slavin & Holzer (1981) |
| Electron temperature |  |
133 300 | K | Slavin & Holzer (1981) |
| Interplanetary magnetic field | Bsw = (Bx, By, Bz) | (0, By, 0) | nT | See Table 2 for values of By |
| Neutral atmosphere | One species, H2O | |||
| Cometocentric radial distance | r |  |
m | |
| Neutral outgassing model (Haser model) | ns |  |
m−3 | Haser (1957) |
| H2O outgassing rate | Q0 | 4.14 × 1027 | s−1 | Hansen et al. (2016) |
| Neutral outgassing radial speed | v0 | 700 | m s−1 | Hansen et al. (2016) |
| Photoionization frequency | fPI | 1.63 × 10−7 | s−1 | Huebner & Mukherjee (2015) |
| Characteristic Haser scale length | λ = v0∕fPI | 4.29 × 106 | km | |
| Processes | ||||
| Charge-exchange cross section in H+ + H2O | σCX | σCX(Ei) | m2 | Simon Wedlund et al. (2017) |
| Electron ionization reaction rate in H2O | kEI | 9.79 × 10−15 | m3 s−1 | Cravens et al. (1987) |
| Electron recombination reaction rate in H2O | kER | 2.06 × 10−14 | m3 s−1 | Hollenbach et al. (2012) |
| Ion-neutral drag coefficient for H2O + H2O+ | ki,s | 1.5 × 10−15 | m3 s−1 | Rubin et al. (2014) |
| Simulation | ||||
| Time step | Δt | 0.037 | s | |
| Maximum resolution | Δxmin | 250 | km | |
| Base resolution | Deltaxmax | 2000 | km | |
| Maximum signal speed | Δxmin∕Δt | 6756 | km s−1 | |
| Resistivity factor at Δxmax | ηmax | 21 610 | Ohm m | See Sect. 2.2.1, Eq. (4) |
| Simulation domain X extent | X | [−1, 11] × 103 | km | |
| Simulation domain Y, Z extent | Y, Z | [−25, 25] × 103 | km | |
| Macroparticles per cell, upstream solar wind |  |
40 | #/Δx3 | |
| Data collection | ||||
| Simulation quasi-stationary time | tinit | 350 | s | |
| Simulation end time | tend | 600 | s | |
| Particle collection period | Δtint | 400–600 | s | |
| Radius of particle collection sphere, | rcoll | 200 | km | |
| centered on the nucleus | ||||
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