Three-dimensional Martian ionosphere model: II. Effect of transport processes due to pressure gradients

Abstract

To study the transport of the ionospheric plasma on Mars, we have included a 3-D multifluid dynamical core in a Martian general circulation model. Vertical transport modifies the ion density abovẽ 160 km on the dayside, especially the ions produced at high altitudes like O + , N + , and C + . Near the exobase, the dayside to nightside flow velocity reaches few hundreds of m/s, due to a large horizontal pressure gradient. Comparison with Mars Express/Analyzer of Space Plasmas and Energetic Atoms-3 measurements between 290 and 500 km suggests that this flow could account for at least 20% of the flow produced by the solar wind. This flow is not sufficient to populate substantially the nightside ionosphere at high altitudes, in agreement with recent observations, because of a strong nightside downward flow produced by vertical pressure gradient. The O 2 + and NO + ion densities on the nightside at low altitudes (~130 km) are modified by this downward flow, compared to simulated densities without ion dynamics, while other ions are lost by chemical reactions. Variability at different time scales (diurnal, seasonal, and solar cycles) are studied. We simulate diurnal and seasonal variations of the ionospheric composition due to the variability of the neutral atmosphere and solar flux at the top of the atmosphere. The ionospheric dynamics are not strongly affected by seasons and solar cycles, and the retroaction of the ionosphere on the neutral atmosphere temperature and velocity is negligible compared to other physical processes below the exobase.

Day‐to‐night transport in the Martian ionosphere: Implications from total electron content measurements

“…Therefore, the solid body rotation model presented in section 4.1 is comparable to the González‐Galindo et al [] model, and the zonal transport model in section 4.2 serves as one particular case of the Chaufray et al [] model that ignores meridional flow. All works reflect properly the expected situation of a quick depletion of the ionospheric content as passing across the terminator in the case of solid body rotation only and a delayed depletion in the case of strong nightward transport [see Chaufray et al , , Figure 8]. Chaufray et al [] derived a characteristic day‐to‐night flow velocity of several 10 2 m s −1 for both ions and electrons, which is significantly lower than the value of ≈1.9 km s −1 reported in section 4.2.…”

“…Ma et al [] in their multispecies magnetohydrodynamic (MHD) modeling calculated the day‐to‐night ion transport rate to be ≈3 × 10 24 s −1 for high solar activity and ≈1 × 10 24 s −1 for low solar activity, driven by pressure gradient and convective electric field under nominal Solar Wind (SW) conditions. More recently, Chaufray et al [] made three‐dimensional modeling of day‐to‐night transport in the Martian ionosphere driven by pressure gradient and collisional coupling with the neutral winds. They calculated the day‐to‐night ion flow velocity to be ≈ (0.5–1) km s −1 at an altitude of ≈250 km for intermediate solar activity.…”

Dawn/Dusk Asymmetry of the Martian UltraViolet Terminator Observed Through Suprathermal Electron Depletions

“…Journal of Geophysical Research: Space Physics neutral atmosphere between the duskside and the dawnside driven by cooler temperatures at dawn than at dusk (Chaufray et al, 2014;González-Galindo et al, 2013). Neutrals on the duskside are then expected to have a higher scale height and consequently a greater density at high altitudes than on the dawnside.…”

On Mars's Atmospheric Sputtering After MAVEN's First Martian Year of Measurements

“…In order to compare these effects to other atmospheric sources of the exosphere or atmospheric escape, EGM is also used to describe the contribution of dissociative recombination of O 2 + to the exosphere and atmospheric escape, the 3-D spatial distribution of the O 2 + being provided by LMD-GCM (Chaufray et al, 2014). In order to compare these effects to other atmospheric sources of the exosphere or atmospheric escape, EGM is also used to describe the contribution of dissociative recombination of O 2 + to the exosphere and atmospheric escape, the 3-D spatial distribution of the O 2 + being provided by LMD-GCM (Chaufray et al, 2014).…”

“…The exospheric density profiles of CO 2 and Ar are close to each other on the nightside, at dawn, and at the poles. As a consequence, near midnight, the main source of exospheric CO 2 and Ar is sputtering, dissociative recombination being significantly reduced due to the very low O 2 + density at such local time (few orders smaller than on the dayside; Chaufray et al, 2014). This divergence is due to a change Because the profiles in Figure 2 are built from three sources: a component from the thermal expansion of the atmosphere, a component induced by dissociative recombination of O 2 + and one by sputtering, we separate these contributions in Figure 3 for two of the profiles displayed in Figure 2.…”