Hot oxygen corona at Mars and the photochemical escape of oxygen: Improved description of the thermosphere, ionosphere, and exosphere

Abstract

The Mars Adaptive Mesh Particle Simulator model is coupled with the Mars Global Ionosphere Thermosphere Model for the first time to provide an improved description of the Martian hot O corona based on our modeling studies of O2+ dissociative recombination. A total of 12 cases comprising three solar activity levels and four orbital positions is considered to study the solar cycle and seasonal variability. The newly coupled framework includes two additional thermospheric species and adopts a realistic forward scattering scheme using the angular differential cross sections. We present the effects of these changes on the resulting hot O corona and escape rate. A comparison between the simulated hot O corona and the recent observations from the ALICE/Rosetta instrument showed a reasonable agreement, considering the large uncertainties in the data. We assume that some discrepancies near the transition altitude may be originated from the averaging over the altitude range, where the cold and hot O densities become comparable. The revised O escape rates by our new coupled framework range from ~1.21 × 1025 s−1 to ~5.43 × 1025 s−1.

Solar wind interaction with the Martian upper atmosphere: Crustal field orientation, solar cycle, and seasonal variations

“…Basically, the hot oxygen has a thermal speed larger than the local background thermal speed (calculated based on M-GITM thermospheric profile [Bougher et al, 2015]), indicating the scale height of hot oxygen is larger than that of the cold oxygen [e.g., Ma et al, 2004, Figures 1 and 2]. However, the hot oxygen can be converted to the thermal oxygen via collisions with other background cold neutral species before it escapes to interplanetary space [Lee et al, 2013]. It is noteworthy that when we mention the cold heavy ionospheric molecular/atomic ions, it refers to those ionized from the cold molecular/atomic neutrals.…”

“…The MF-MHD code solves separate continuity, momentum, and energy equations for each ion species [Powell et al, 1999;Glocer et al, 2009;Najib et al, 2011;Tóth et al, 2012;Dong et al, 2014]. Please refer to Lee et al [2013Lee et al [ , 2014aLee et al [ , 2014b for the detailed study of one-way coupling between M-GITM and M-AMPS (as indicated by the dashed line in Figure 1); i.e., M-GITM provides thermosphere/ionosphere background as an input into the M-AMPS exosphere model. These calculations are carried out for 22 cases with combinations of different crustal field orientations (four cases without crustal field), solar cycle, and Martian seasonal conditions.…”

“…Here we focus on the one-way coupling indicated by the solid line. For the detailed study of one-way coupling between M-GITM and M-AMPS (dashed line), please refer to Lee et al [2013Lee et al [ , 2014aLee et al [ , 2014b.…”

“…In order to reproduce a realistic asymmetric corona of hot species from observations, a 3-D global kinetic exosphere model is required, especially above the exobase (Knudsen number, K n ≈ 1) where the fluid assumption usually fails [Lee et al, 2013]. One such model is the Mars exosphere Monte Carlo model Adaptive Mesh Particle Simulator (M-AMPS) [Tenishev and Combi, 2008;Lee et al, 2013Lee et al, , 2014aLee et al, , 2014b, which can generate a 3-D hot (e.g., oxygen and carbon) corona with detailed asymmetric structure. In order to capture these 3-D asymmetries, 3-D thermosphere/ionosphere inputs from a validated ground-to-exobase atmospheric model (e.g., M-GITM) are essential (see Figure 1 for more detail).…”

Pickup ion measurements by MAVEN: A diagnostic of photochemical oxygen escape from Mars

“…Several hot O transport models have been constructed to simulate this, including two-stream, Monte Carlo, and DSMC (Direct Simulation Monte Carlo) models [e.g., Nagy and Cravens, 1988;Ip, 1990;Kim et al, 1998;Hodges, 2000;Hać, 2009, 2014;Valeille et al, 2009aValeille et al, , 2009bValeille et al, , 2010aValeille et al, , 2010bYagi et al, 2012;Lee et al, 2013;Gröller et al, 2014]. But these photochemical escape rate calculations vary by about 2 orders of magnitude as summarized in Table 3 of Fox and Hać [2009], and there is a lack of direct observational constraint on photochemical escape models.…”