The composition of Mars' topside ionosphere: Effects of hydrogen
火星上部电离层的组成：氢的影响

1 Introduction  1 简介

[2] The composition of the ionized component of a planet's atmosphere is dependent on the composition of its neutral counterpart. The atmospheric composition of Mars has been measured remotely and in situ with too little frequency to result in any definitive global map of the major and minor constituents. Hence, measurements from various instruments and spacecraft are often pooled to provide a representative picture of the neutral atmosphere.
[2]行星大气中电离成分的成分取决于其中性对应物的成分。火星大气成分的远程和现场测量频率太低，无法得出主要和次要成分的任何明确的全球地图。因此，来自各种仪器和航天器的测量结果通常被汇集在一起​​，以提供中性大气的代表性图像。

[3] Early efforts of remotely measuring the Martian upper atmosphere revealed CO₂, H₂O, and CO [Kuiper, 1952; Kaplan et al., 1964, 1969; Young and Young 1977]. While Mariner 4 quantified the total pressure at Mars [Kliore et al., 1965], Mariners 6, 7, and 9 and Mars-3 took in situ spectra that quantified the abundance of H, CO, and O at ~220 km [Anderson and Hord, 1971, 1972; Barth et al., 1971, 1972; Dementyeva et al., 1972; Strickland et al., 1972; Anderson, 1974; Moos, 1974]. A few decades after the first flyby of Mars, remote sensing of atomic hydrogen Lyman-α emissions was made by the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer (FUSE). The resulting measurements quantified H and H₂ abundances in the Martian atmosphere [Krasnopolsky, 2000, 1998; Krasnopolsky and Feldman, 2001]. More recently, the Mars Express (MEX) mission made spectral measurements of H and O at 200 km using the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars instrument [Bertaux, 2000; Chaufray et al., 2007, 2008, 2009; Valeille et al., 2009] and the Analyzer of Space Plasma and Energetic Atoms instrument [Galli et al., 2006]. Furthermore, the Rosetta flyby of Mars during a gravity assist maneuver made spectral detections of H and O at exospheric altitudes [Feldman et al., 2011].
[3]早期对火星高层大气进行遥测的工作揭示了CO ₂ 、H ₂ O和CO [ Kuiper , 1952 ；卡普兰等人， 1964 年， 1969 年；年轻和年轻1977 ]。虽然水手 4 号量化了火星的总压力 [ Kliore 等人， 1965 ]，但水手 6、7、9 和 Mars-3 采集了原位光谱，量化了约 220 公里处 H、CO 和 O 的丰度 [ Anderson和霍德， 1971 年、 1972 年；巴特等人， 1971，1972 ；德门蒂耶娃等人， 1972 ；斯特里克兰等人， 1972 ；安德森， 1974 ；穆斯， 1974 ]。第一次飞越火星几十年后，哈勃太空望远镜和远紫外光谱探测器（FUSE）对原子氢莱曼-α发射进行了遥感。由此产生的测量结果量化了火星大气中 H 和 H _{2 的}丰度 [ Krasnopolsky , 2000 , 1998 ;克拉斯诺波尔斯基和费尔德曼， 2001 ]。 最近，火星快车 (MEX) 任务使用火星大气特征光谱仪对 200 公里处的 H 和 O 进行了光谱测量 [ Bertaux , 2000 ； Chaufray等人， 2007、2008、2009 ； Valeille 等人， 2009 年] 以及空间等离子体和高能原子分析仪仪器 [ Galli 等人， 2006 年]。此外，罗塞塔号在重力辅助机动过程中飞越火星，在外层高度对 H 和 O 进行了光谱检测 [ Feldman et al ., 2011 ]。

[4] To date, the Viking 1 and 2 Landers mark the only spacecraft to successfully deliver in situ measurements of the atmosphere and ion composition of Mars between 120 and 200 km [Nier and McElroy, 1976]. Viking neutral mass spectrometers measured abundances of major species, CO₂, N₂, Ar, CO, O₂, and NO, and analyzed upper limits of mixing ratios of minor species such as H₂ and He. Atomic oxygen was also detected as a major neutral species, but quantitative in situ measurements could not be made due to contamination of the instrument by terrestrial sources [Nier et al., 1976; Nier and McElroy, 1976; Nier and McElroy, 1977]. The Viking Landers also measured ion density profiles of O⁺, CO₂⁺, and O⁺ [Hanson et al., 1977].
[4]迄今为止，维京 1 号和 2 号着陆器是唯一成功对 120 至 200 公里之间的火星大气和离子成分进行原位测量的航天器 [ Nier 和 McElroy ， 1976 ]。 Viking中性质谱仪测量了主要物种CO ₂ 、N ₂ 、Ar、CO、O ₂和NO的丰度，并分析了次要物种如H ₂和He的混合比上限。原子氧也被检测为主要的中性物质，但由于仪器受到陆地来源的污染而无法进行定量原位测量[ Nier等， 1976 ；尼尔和麦克尔罗伊， 1976 ；尼尔和麦克尔罗伊， 1977 ]。 Viking Landers 还测量了 O ⁺ 、CO ₂ ⁺和 O ⁺的离子密度分布[ Hanson et al ., 1977 ]。

[5] Preceding the H₂ measurements at Mars mentioned above, ionospheric simulations neglected to include minor atomic and molecular hydrogen species [e.g., Hanson et al., 1977; Kong and McElroy, 1977; McElroy et al., 1977; Chen et al., 1978; Fox and Dalgarno, 1979; Singh and Prasad, 1983; Krasnopolsky, 1993a, 1993b; Nair et al., 1994; Krasnopolsky, 1995; Fox et al., 1996]. FUSE measurements of Martian H₂ revealed its dominance in the neutral atmosphere above 250 km [Krasnopolsky et al., 1998]. Since molecular hydrogen is chemically reactive with its surrounding ions, it can have major effects on the composition of the ionosphere.
[5]在上述火星 H ₂测量之前，电离层模拟忽略了少量原子和分子氢物种 [例如， Hanson 等人， 1977 年；孔和麦克尔罗伊， 1977 ；麦克尔罗伊等人， 1977 ；陈等人， 1978 ；福克斯和达尔加诺， 1979 ；辛格和普拉萨德， 1983 ；克拉斯诺波尔斯基， 1993a ， 1993b ；奈尔等人， 1994 ；克拉斯诺波尔斯基， 1995 ；福克斯等人， 1996 ]。火星 H ₂的 FUSE 测量揭示了其在 250 公里以上中性大气中的主导地位 [ Krasnopolsky et al ., 1998 ]。由于氢分子会与其周围的离子发生化学反应，因此它会对电离层的组成产生重大影响。

[6] The H₂ mixing ratio was determined with some uncertainty to vary between 20 and 50 ppm at 80 km [Krasnopolsky et al., 1998; Krasnopolsky and Feldman, 2001; Krasnopolsky, 2002, 2003; Fox and Yeager, 2009]. Fox and Bakalian [2001] were among the first to address the quantitative effects of H₂ on the Martian atmosphere. They found that H₂ would affect the secondary ion chemistry of N₂H⁺, OH⁺, HCO⁺, and HCO₂⁺, and they concluded that the adopted mixing ratio of 40 ppm was too large. A follow-up study by Fox [2003] showed the effects of varying the abundance of H₂ on O⁺, CO₂⁺, N₂⁺, and CO⁺. In an effort to improve agreement of modeled O⁺ densities with those measured by Viking below 200 km, the mixing ratio of H₂ was varied from 4, 10, 15, 40 to 100 ppm. Due to the high reactivity of H₂ with O⁺, it was found that the lower the mixing ratio and the higher the modeled O⁺ density, the better is the match between models and Viking measurements. However, there has been relatively little follow-up on the importance of hydrogen on ion composition [Krasnopolsky, 2002; Fox, 2004a, 2004b, 2005; Fox and Yeager, 2006, 2009; Fox and Hać, 2009]. No study to date has explored systematically the effects of H and H₂ chemistry on the upper ionosphere of Mars.
[6] H ₂混合比确定为具有一定的不确定性，在 80 km 处变化范围为 20 至 50 ppm [ Krasnopolsky et al ., 1998 ；克拉斯诺波尔斯基和费尔德曼， 2001 ；克拉斯诺波尔斯基， 2002年， 2003年；福克斯和耶格尔， 2009 ]。 Fox 和 Bakalian [ 2001 ] 是最早研究 H ₂对火星大气的定量影响的人之一。他们发现H ₂会影响N ₂ H ⁺ 、OH ⁺ 、HCO ⁺和HCO ₂ ⁺的二次离子化学，并得出结论，采用的40 ppm 的混合比太大。 Fox [ 2003 ] 的后续研究显示了不同 H ₂丰度对 O ⁺ 、CO ₂ ⁺ 、N ₂ ⁺和 CO ⁺的影响。为了提高模拟的 O ⁺密度与 Viking 在 200 km 以下测量的密度的一致性，H ₂的混合比从 4、10、15、40 到 100 ppm 变化。由于H ₂与O ⁺的高反应性，我们发现混合比越低，模拟的O ⁺密度越高，模型与Viking 测量之间的匹配越好。 然而，关于氢对离子组成的重要性的后续研究相对较少[ Krasnopolsky ， 2002 ；福克斯， 2004a ， 2004b ， 2005 ；福克斯和耶格尔，2006，2009 ； Fox 和 Hać ， 2009 年]。迄今为止还没有研究系统地探讨过 H 和 H ₂化学对火星上层电离层的影响。

[7] The objective of this work is to analyze the combined effects of atomic and molecular hydrogen chemistry at Mars, with particular attention to the topside ionosphere. Section 2 describes the model customized to include atomic and molecular hydrogen chemistry for use in this work. Section 3 shows the main results of the simulations using two sensitivity experiments. In Section 4, the model results are compared with measurements and other models and then discussed. Conclusions are drawn in Section 5.
[7]这项工作的目的是分析火星上原子和分子氢化学的综合影响，特别关注上部电离层。第 2 节描述了本工作中使用的定制模型，包括原子和分子氢化学。第 3 节显示了使用两个灵敏度实验进行模拟的主要结果。在第 4 节中，将模型结果与测量结果和其他模型进行比较，然后进行讨论。第 5 节得出结论。

2 Model Description  2 型号说明

[8] Planetary atmospheric and ionospheric models are abundant for Mars [Bougher et al., 2008; González-Galindo et al., 2011; Haider et al., 2011]. One-dimensional (1-D) models represent simplified yet quantitative tools for gaining insight to the major neutral and ionized constituents of an atmosphere, as well as to the physical processes controlling those regions. An existing 1-D model has been adapted for this study. This model was first used to analyze the variability in the photochemical regions of the Martian ionosphere [Martinis et al., 2003]. The model was later upgraded to include plasma diffusion and was used for a study of simultaneous Mars Global Surveyor (MGS) and MEX radio occultation data sets, and to simulate and analyze the effects of flares on the ionosphere at Mars [Mendillo et al., 2011; Lollo et al., 2012].
[8]火星的行星大气和电离层模型非常丰富[ Bougher et al ., 2008 ；冈萨雷斯-加林多等人， 2011 ；海德尔等人， 2011 ]。一维 (1-D) 模型代表了简化但定量的工具，可用于深入了解大气中的主要中性和电离成分，以及控制这些区域的物理过程。本研究已采用现有的一维模型。该模型首先用于分析火星电离层光化学区域的变化[ Martinis et al ., 2003 ]。该模型后来升级为包括等离子体扩散，并用于研究同步火星全球勘测者 (MGS) 和 MEX 无线电掩星数据集，并模拟和分析耀斑对火星电离层的影响 [ Mendillo 等人， 2011年； Lollo 等人， 2012 年]。

[9] The simulations of this work are conducted for the same conditions used by Mendillo et al. [2011] for the MGS dataset: solar minimum conditions (F_10.7 ~ 84), a Mars-Sun distance of 1.5943 AU, solar declination of 19.8°, latitude of 66.7° north, at summer solstice with a resulting SZA ~ 47° at local noon. The model is run for 2 sols (Martian days), and results from the second day's run at local noon are shown.
[9]这项工作的模拟是在Mendillo 等人使用的相同条件下进行的。 [ 2011 ] 对于 MGS 数据集：太阳极小条件（ F _10.7 ~ 84），火星-太阳距离 1.5943 AU，太阳赤纬 19.8°，北纬 66.7°，夏至时 SZA ~ 47°当地中午。该模型运行了 2 个太阳日（火星日），并显示了第二天在当地中午运行的结果。

[10] A detailed description of the model can be found in Mendillo et al. [2011]. To summarize, this model simulates the Martian ionosphere between 80 and 400 km and takes as input (1) a neutral atmosphere consisting of CO₂, O, N₂, CO, and H₂ as described by version 4 of the Mars Climate Database (MCD) [Forget et al., 1999; Lewis et al. 1999], (2) an exospheric neutral temperature from the MCD, (3) absorption and ionization cross sections from Verner and Yakovlev [1995] and Verner et al. [1996] for wavelengths 1.86–4.92 nm and from Schunk and Nagy [2009] for wavelengths 5.05–105 nm, and (4) solar irradiance for wavelengths 1.86–105 nm from Solar2000 [Tobiska, 2004] that is scaled to Mars' location. Empirical representations of secondary ionization yield and plasma temperatures were developed from the parameterizations based upon the detailed calculations of Fox et al. [1996] and Nicholson et al. [2009]. The secondary ionization ratio varies smoothly from 0.3 in the upper boundary to 11 in the lower boundary. These representations were optimized via constraints by MGS and MEX radio occultation profiles [Mendillo et al., 2011].
[10]该模型的详细描述可以在Mendillo 等人中找到。 [ 2011 ]。总而言之，该模型模拟 80 至 400 km 之间的火星电离层，并采用由 CO ₂ 、O、N ₂ 、CO 和 H ₂组成的中性大气作为输入 (1)，如火星气候数据库第 4 版所述 ( MCD）[ Forget 等人， 1999 ；刘易斯等人。 1999 ]，(2) 来自 MCD 的外层中性温度，(3) 来自Verner 和 Yakovlev [ 1995 ] 以及Verner 等人的吸收和电离截面。 [ 1996 ] 波长 1.86–4.92 nm，来自Schunk 和 Nagy [ 2009 ] 波长 5.05–105 nm，以及 (4) 波长 1.86–105 nm 的太阳辐照度，来自 Solar2000 [ Tobiska , 2004 ]，按比例缩放至火星位置。二次电离产率和等离子体温度的经验表示是根据Fox 等人的详细计算从参数化中得出的。 [ 1996 ] 和尼克尔森等人。 [ 2009 ]。二次电离比从上边界的 0.3 到下边界的 11 平滑变化。这些表示通过 MGS 和 MEX 射电掩星剖面的约束进行了优化 [ Mendillo 等人， 2011 ]。

[11] The model solves equations for generating a neutral atmosphere between 80 and 400 km based on mixing ratios at 80 km that propagate neutral species concentrations upwards via molecular and eddy diffusion [Krasnopolsky, 2002]. The volume mixing ratios supplied by the MCD are more reliable at lower altitudes. The resulting neutral atmosphere that is derived compares well with Viking Lander measurements for overlapping species at overlapping altitudes. Five ions are generated via photo-ionization and photochemistry: O₂⁺, O⁺, CO₂⁺, N₂⁺, and NO⁺. The coupled continuity and momentum equations are then solved along the vertical dimension using solar production, chemical production and loss, and vertical transport with ion-neutral collisions to obtain ion densities and velocities as a function of time. The model time steps are orders of magnitude smaller than photochemical and transport timescales. Solar wind effects upon the ionospheric plasma are not in the model; i.e., it is assumed that the solar wind plasma lies above the top altitude boundary of 400 km. However, the altitude of the region separating solar wind from planetary plasma at Mars is not well defined and could be lower than the model's upper boundary altitude [Mitchell et al., 2001; Withers, 2009], and so the results of this work are summarized for ion composition at 250 km, 300 km and 350 km.
[11]该模型根据 80 公里处的混合比求解在 80 至 400 公里之间生成​​中性大气的方程，通过分子和涡流扩散向上传播中性物质浓度 [ Krasnopolsky ， 2002 ]。 MCD 提供的体积混合比在低海拔地区更可靠。由此产生的中性大气与维京着陆器在重叠高度上对重叠物种的测量结果进行了很好的比较。通过光电离和光化学产生五种离子：O ₂ ⁺ 、O ⁺ 、CO ₂ ⁺ 、N ₂ ⁺和NO ⁺ 。然后使用太阳能产生、化学产生和损失以及离子中性碰撞的垂直传输沿垂直维度求解耦合的连续性和动量方程，以获得作为时间函数的离子密度和速度。模型时间步长比光化学和传输时间尺度小几个数量级。太阳风对电离层等离子体的影响不在模型中；即，假设太阳风等离子体位于400公里的最高高度边界之上。然而，火星上将太阳风与行星等离子体分开的区域的高度尚未明确定义，并且可能低于模型的上边界高度[ Mitchell et al ., 2001 ; Withers ， 2009 ]，因此总结了 250 km、300 km 和 350 km 处离子组成的工作结果。

[12] A similar modeling approach to the one used here was applied to Saturn's ionosphere. The Saturn model uses the same numerical techniques for plasma transport as used for Mars and has been validated using Cassini electron density profiles, as well as checked for consistency using a 3-D general circulation model [Moore et al., 2004; Müller-Wodarg et al., 2006; Moore and Mendillo, 2007; Moore et al., 2010, 2012].
[12]土星电离层采用了与此处使用的类似的建模方法。土星模型使用与火星相同的等离子体传输数值技术，并已使用卡西尼号电子密度分布进行了验证，并使用 3-D 大气环流模型检查了一致性[ Moore 等人， 2004 年；穆勒-沃达格等人， 2006 ；摩尔和门迪略， 2007 ；摩尔等人， 2010，2012 ]。

2.1 Updates to the Neutral Atmosphere
2.1 中性氛围的更新

[13] The same neutral atmosphere derived from the MCD (version 4.3) and used in Mendillo et al. [2011] was used for this work with some additions. The MCD is an online resource of Martian atmospheric parameters derived from a 3-D general circulation model. The MCD is a collaborative effort developed at the Laboratoire de Meteorologie Dynamique du CNRS (Paris, France), Open University (UK), Oxford University (UK), and the Instituto de Astrofisica de Andalucia (Spain). The parameters available for lookup in the model are neutral density, pressure, temperature, and turbulent kinetic energy; surface temperature, pressure, and CO₂ ice layer; volume mixing ratios of CO₂, CO, H₂, O, N₂, H₂O ice, and H₂O vapor; 3-D neutral wind components; water ice and vapor columns; solar and thermal radiative fluxes and dust optical depth. The 3-D MCD offers these parameters as a function of dust scenario, latitude, longitude, local time, and altitude ranging from the surface up to 230 km [Forget et al., 1999; Lewis et al. 1999; Angelats i Coll et al., 2005; González-Galindo et al., 2005; Millour et al., 2011]. The database is readily available for reference at http://www-mars.lmd.jussieu.fr/. The MCD is validated with measurements from MGS Thermal Emission Spectrometer for surface temperature, atmospheric temperature, and water vapor column; radio occultation measurements using the ultra-stable oscillator on MGS for atmospheric temperature; and Viking Landers and Pathfinder for surface pressure.
[13]相同的中性气氛源自 MCD（版本 4.3）并用于Mendillo 等人。这项工作使用了 [ 2011 ]，并进行了一些补充。 MCD 是从 3-D 大气环流模型导出的火星大气参数的在线资源。 MCD 是法国国家科学研究中心气象动态实验室（法国巴黎）、开放大学（英国）、牛津大学（英国）和安达卢西亚天体研究所（西班牙）合作开发的成果。模型中可查找的参数有中性密度、压力、温度和湍流动能；表面温度、压力和CO ₂冰层； CO ₂ 、CO、H ₂ 、O、N ₂ 、H ₂ O冰和H ₂ O蒸气的体积混合比； 3-D中性风分量；水冰柱和蒸气柱；太阳和热辐射通量以及尘埃光学深度。 3-D MCD 提供这些参数作为灰尘场景、纬度、经度、当地时间和海拔的函数，范围从表面到 230 公里 [ Forget 等人， 1999 年；刘易斯等人。 1999年； Angelats i Coll 等， 2005 ；冈萨雷斯-加林多等人， 2005 ；米卢尔等人， 2011 ]。该数据库可供参考：http: //www-mars.lmd.jussieu.fr/ 。 MCD 通过 MGS 热发射光谱仪的表面温度、大气温度和水蒸气柱测量进行验证；使用 MGS 上的超稳定振荡器进行无线电掩星测量，以测量大气温度；以及 Viking Landers 和 Pathfinder 用于表面压力。

[14] The 1-D model of Mendillo et al. [2011], and this work, used MCD-provided mixing ratios of CO₂, O, N₂, CO, and H₂ to generate a neutral atmosphere. The resulting CO₂, O, N₂, and CO profiles agree with the density profiles measured by the Viking Landers. H₂ densities are more challenging to validate as there are no in situ measurements to compare with. FUSE detections of Martian H₂ from mostly Lyman-β photons gave a mixing ratio for H₂ of 15 ± 5 ppm and a corresponding density of 10⁵ cm⁻³ at ~220 km for solar maximum conditions [Krasnopolsky and Feldman, 2001]. Densities of molecular hydrogen at 250 km were modeled to be ~2–50 × 10⁵ cm⁻³ (T_∞ ~ 200 K) and ~1–5 × 10⁵ cm⁻³ (T_∞ = 350 K) for solar minimum and maximum conditions, respectively, where T_∞ is the exospheric temperature [McElroy et al., 1977; Krasnopolsky, 2000, 1998; Krasnopolsky and Feldman, 2001; Fox, 2003]. For solar minimum conditions, there is about an order of magnitude difference in the limits of estimated neutral molecular hydrogen in the Martian atmosphere. Presently, H₂ mixing ratios in the MCD are still under development [F. Forget, 2011, personal communication]. At 80 km, MCD provides 16 ppm of molecular hydrogen that results in a concentration of 3 × 10⁶ cm⁻³ at 200 km (for T_∞ = 205 K), close to the upper limit given by other models. The molecular hydrogen mixing ratio in this model is therefore treated as a free parameter with densities at 200 km ranging between 10⁵ and 10⁶ cm⁻³. This corresponds to a mixing ratio of 1.6 and 16 ppm at 80 km.
[14] Mendillo 等人的一维模型。 [ 2011 ] 和这项工作，使用 MCD 提供的 CO ₂ 、O、N ₂ 、CO 和 H ₂的混合比例来生成中性气氛。所得的 CO ₂ 、O、N ₂和 CO 分布与 Viking Landers 测量的密度分布一致。 H ₂密度的验证更具挑战性，因为没有可比较的原位测量结果。 FUSE 对火星 H ₂的检测主要来自 Lyman-β 光子，给出了 H ₂的混合比为 15 ± 5 ppm，在太阳极大值条件下，在约 220 km 处相应的密度为 10 ⁵ cm ^-3 [ Krasnopolsky 和 ​​Feldman ， 2001 ]。 250 km 处的分子氢密度被建模为 ~2–50 × 10 ⁵ cm ^-3 ( T _∞ ~ 200 K) 和 ~1–5 × 10 ⁵ cm ^-3 ( T _∞ = 350 K) 太阳极小期和分别为最大条件，其中T _∞是外层温度 [ McElroy 等人， 1977 ；克拉斯诺波尔斯基， 2000年， 1998年；克拉斯诺波尔斯基和费尔德曼， 2001 ；福克斯， 2003 ]。对于太阳极小值条件，火星大气中估计的中性分子氢的极限存在大约一个数量级的差异。目前，MCD 中的 H ₂混合比例仍在开发中[ F. 忘记了，2011，个人通讯]。在 80 km 处，MCD 提供 16 ppm 的分子氢，导致在 200 km 处浓度为 3 × 10 ⁶ cm ^-3 （对于T _∞ = 205 K），接近其他模型给出的上限。因此，该模型中的分子氢混合比被视为自由参数，200 km处的密度范围在10 ⁵和10 ⁶ cm ^-3之间。这对应于 80 公里时的混合比为 1.6 和 16 ppm。

[15] To the MCD mixing ratios, two more neutral species, H and Ar, have been added to expand the ion-neutral chemistry in this work. An atomic hydrogen neutral density profile was added by incorporating a volume mixing ratio at 80 km for H and then using the existing formulae to generate concentrations as a function of altitude up to 400 km. Since there are no in situ measurements of atomic hydrogen at Mars, the H neutral density at ~220 km is constrained to match Lyman-α airglow measurements made by spacecraft. A summary of such measurements is reviewed in Table 1. The density of H at 220 km during the solar minimum conditions modeled here is ~2 × 10⁵ cm⁻³. At higher altitudes, the extrapolated density for H compares well with those of other models for similar conditions [Krasnopolsky, 2002; Fox, 2003; Chaufray et al., 2007].
[15]在 MCD 混合比中，添加了两种中性物质 H 和 Ar，以扩展本工作中的离子中性化学。通过合并 80 km 处 H 的体积混合比，然后使用现有公式生成高达 400 km 高度的浓度函数，添加了原子氢中性密度分布。由于火星上没有原子氢的原位测量，约 220 公里处的 H 中性密度仅限于与航天器进行的莱曼-α 气辉测量相匹配。表1总结了此类测量结果。这里模拟的太阳极小期条件下 220 km 处的 H 密度约为 2 × 10 ⁵ cm ^-3 。在较高海拔处，H 的外推密度与类似条件下其他模型的外推密度相当[ Krasnopolsky ， 2002 ；福克斯， 2003 ； Chaufray 等人， 2007 年]。

Table 1. A Brief Survey of Measured Exospheric Atomic Hydrogen at Mars Between 200 and 400 km
表 1.对火星 200 至 400 公里处测量的外层原子氢的简要调查

ρexo (cm−3) ρ exo (cm -3 )	T∞a (K) T ∞ a (K)	Solar activity  太阳活动	Spacecraft  宇宙飞船	Source  来源
2 × 105  2×10 5	200C	solar minimum  太阳极小期	Rosetta  罗塞塔	Feldman et al. [2011] 费尔德曼等人。 [ 2011 ]
9 × 104  9×10 4	260H	solar minimum  太阳极小期	Rosetta  罗塞塔	Feldman et al. [2011] 费尔德曼等人。 [ 2011 ]
104	>600H  % 3E600H	solar minimum  太阳极小期	ASPERA-3/NDP	Galli et al. [2006] 加利等人。 [ 2006 ]
1–4 × 105 1–4 × 10 5	200–250	solar minimum  太阳极小期	SPICAM	Chaufray et al. [2008] 乔弗雷等人。 [ 2008 ]
3 × 104  3×10 4	350H	solar maximum  太阳活动极大期	Mariners 6, 7  水手 6, 7	Anderson and Hord [1971] 安德森和霍德[ 1971 ]
2.5 × 104 2.5×10 4	350H	solar maximum  太阳活动极大期	Mariners 6, 7  水手 6, 7	Anderson and Hord [1972] 安德森和霍德[ 1972 ]
6 × 103  6×10 3	350H	solar maximum  太阳活动极大期	Mars-3  火星三号	Dementyeva et al. [1972] 德门蒂耶娃等人。 [ 1972 ]

• ρ_exo is exospheric density which varies little in that altitude range. T_∞ is exospheric temperature.
  ρ _exo是外层密度，在该高度范围内变化很小。 T _∞是外层温度。
• ^a C refers to the cold (photochemically generated) component of atomic hydrogen and H to the hot component (due to charge exchange with the solar wind). In this model, the cold population densities are adopted. Interested readers are referred to Lichtenegger et al. [2004, 2006] for a more complete discussion of the separate populations.
  ^一个 C 指原子氢的冷（光化学产生）成分，H 指热成分（由于与太阳风的电荷交换）。在该模型中，采用冷人口密度。有兴趣的读者可以参考Lichtenegger 等人的文章。 [ 2004，2006 ]对不同人群进行更完整的讨论。

[16] At the time of this writing, the MCD did not include any volume mixing ratios for Ar, O₂, NO, or He, listed here in order of decreasing abundance at 140 km as measured by the Viking Landers [Nier and McElroy, 1977]. Ar has been added with a volume mixing ratio of 60% that of N₂ at 80 km [F. Forget, 2011, personal communication] and agrees with Ar density profiles measured by Viking. O₂, NO, and He neutral species have been neglected in the current model. Ignoring these neutral species has negligible effects (<1%) on the density propagation of the included neutrals. Omitting these species from the model chemistry has similarly negligible effects on the production of major ions (discussed in more detail below).
[16]在撰写本文时，MCD 不包括 Ar、O ₂ 、NO 或 He 的任何体积混合比，此处按 Viking Landers 测量的 140 km 丰度递减顺序列出 [ Nier 和 McElroy ， 1977 ]。 Ar 的添加量为 80 km 处 N ₂的 60% [ F. Forget , 2011, 个人通讯]，并且与 Viking 测量的 Ar 密度分布一致。当前模型中忽略了 O ₂ 、NO 和 He 中性物质。忽略这些中性物质对所包含的中性物质的密度传播的影响可以忽略不计（<1%）。从模型化学中省略这些物质对主要离子的产生的影响同样可以忽略不计（下面将更详细地讨论）。

[17] The resulting neutral atmosphere, adopted from the MCD and adjusted to the constraints set by Mendillo et al. [2011] for the conditions used for MGS, with the addition of atomic H and Ar, is shown in Figure 1. The solid lines show the density profiles as generated for all species under consideration. The shaded region shows the uncertainty in H₂ estimated densities, the limits of which will be used in the first of two sensitivity experiments described in Sections 3.1.1 and 3.2.1. The lower limit of H₂ (dashed line) conforms to values modeled for solar minimum conditions and that are based on FUSE observations of H₂ at high solar activity. The upper limit of H₂ (solid line) is derived from the MCD.
[17]由此产生的中性气氛，采用 MCD 并根据Mendillo 等人设定的约束进行调整。 [ 2011 ] 图1显示了添加原子 H 和 Ar 的 MGS 条件。实线显示了为所考虑的所有物种生成的密度分布。阴影区域显示了 H ₂估计密度的不确定性，其限制将用于第 3.1.1 和3.2.1节中描述的两个灵敏度实验中的第一个。 H ₂的下限（虚线）符合为太阳极小条件建模的值，并且该值基于 FUSE 在太阳活动高时对 H ₂的观测。 H ₂的上限（实线）由MCD导出。

3 Results  3 个结果

[23] The focus of this work is to analyze the topside composition of the Martian ionosphere. Introducing H and H₂ chemistry into the model has led to the generation of the new hydrogenated ions: H⁺, H₂⁺, H₃⁺, OH⁺, HCO⁺, ArH⁺, N₂H⁺, HCO₂⁺, and HOC⁺ as well as CO⁺ and Ar⁺. The ionospheric composition above 200 km clearly varies based on the various simulation conditions used. For the work presented here, all model input is fixed except for two sensitivity parameters that are examined for effects on the upper ionosphere. These two parameters are (1) the H₂ mixing ratio at 80 km and (2) the H⁺ + H₂ charge exchange reaction rate, k₁. The sensitivity tests are run for the case of (a) photochemistry only and (b) photochemistry plus vertical transport, as described next.
[23]这项工作的重点是分析火星电离层的上部成分。将 H 和 H ₂化学引入模型中导致生成新的氢化离子：H ⁺ 、H ₂ ⁺ 、H ₃ ⁺ 、OH ⁺ 、HCO ⁺ 、ArH ⁺ 、N ₂ H ⁺ 、HCO ₂ ⁺和HOC ⁺以及CO ⁺和Ar ⁺ 。根据所使用的各种模拟条件，200 公里以上的电离层成分明显不同。对于此处介绍的工作，除了检查对上部电离层影响的两个灵敏度参数外，所有模型输入都是固定的。这两个参数是(1)80km处的H ₂混合比和(2)H ⁺ + H ₂电荷交换反应速率k ₁ 。灵敏度测试针对 (a) 仅光化学和 (b) 光化学加垂直传输的情况进行，如下所述。

3.1 Effects on Photochemistry
3.1 对光化学的影响

[24] Beginning with the case of photochemistry only (no vertical transport), the sensitivity of the ionosphere to H₂ mixing ratio is tested while k₁ is held constant. Next, the sensitivity to the reaction rate, k₁, is tested while holding the H₂ mixing ratio constant.
[24]从仅光化学的情况（无垂直传输）开始，在k ₁保持恒定的情况下测试电离层对 H ₂混合比的敏感性。接下来，在保持H ₂混合比恒定的情况下测试对反应速率k _{1 的}敏感性。

3.1.1 Sensitivity to H₂
3.1.1 对H _{2 的}敏感性

[25] The sensitivity of the ionospheric composition to H₂ mixing ratio at 80 km is tested by setting the lower limit to 1.6 ppm, and the upper limit to 16 ppm. The former scenario is referred to as case A, and the latter as case B. For this analysis, k₁ is kept fixed at its lower limit of 0, effectively suppressing reaction 1 in Table 2. The difference between using the lower and upper limits of H₂ affects the photoproduction of both H⁺ and H₂⁺ and also the consequent chemistry.
[25]通过将下限设置为1.6 ppm、将上限设置为16 ppm来测试80 km处电离层成分对H ₂混合比的敏感性。前一种情况称为情况A，后者称为情况B。对于该分析， k ₁保持固定在其下限0，有效抑制表2中的反应1。使用H ₂的下限和上限之间的差异影响H ⁺和H ₂ ⁺的光产生以及随后的化学反应。

[26] Figure 2 shows the resulting noontime density profiles for this simulation. In Figure 2a, electron densities show the effects of varying the H₂ neutral density from lower to upper limits given by the dashed to solid lines, respectively. The overall electron density shows insensitivity to H₂ except in the topside ionosphere where it increases with increasing H₂. Figure 2b shows the ion density profile ranges with shaded regions of ion densities, bounded by the dashed and solid lines that correspond to low and high limits of H₂ densities (cases A and B, respectively). As the H₂ mixing ratio increases, the production rates of H₃⁺, OH⁺, N₂H⁺, HCO⁺, and HCO₂⁺ increase, and the loss rates of H⁺, O⁺, N₂⁺, CO⁺, Ar⁺, and CO₂⁺ increase. The ion abundances of H₂⁺, O₂⁺, NO⁺, HOC⁺, and ArH⁺ are affected by both increased production and loss resulting in net effects of increased H₂⁺, decreased HOC⁺, unchanging NO⁺, and varying increases and decreases in O₂⁺ and ArH⁺ with altitude. In response to the increase in H₂, the decreases in CO₂⁺ and O⁺ cause O₂⁺ abundances to decrease below 220 km. The increase in OH⁺ causes the O₂⁺ abundance to increase above that altitude. The ion concentration at each altitude is determined by the choice of H₂ mixing ratio.
[26]图2显示了该模拟生成的中午密度分布图。在图2a中，电子密度显示了H ₂中性密度从下限到上限变化的影响，分别由虚线到实线给出。总体电子密度显示出对 H ₂不敏感，但顶部电离层除外，其随着 H _{2 的}增加而增加。图2b显示了离子密度分布范围，其中离子密度的阴影区域由对应于H ₂密度的下限和上限的虚线和实线界定（分别为情况A和B）。随着H ₂混合比例的增加，H ₃ ⁺ 、OH ⁺ 、N ₂ H ⁺ 、HCO ⁺和HCO ₂ ⁺的生成率增加，而H ⁺ 、O ⁺ 、N ₂ ⁺ 、CO ⁺的损失率增加。 、Ar ⁺ 、CO ₂ ⁺增加。 H ₂ ⁺ 、O ₂ ⁺ 、NO ⁺ 、HOC ⁺和 ArH ⁺的离子丰度受到产量增加和损失的影响，导致 H ₂ ⁺增加、HOC ⁺减少、NO ⁺不变和变化增加的净效应O ₂ ⁺和ArH ⁺随着海拔高度的增加而减少。 响应于H ₂的增加，CO ₂ ⁺和O ⁺的减少导致O ₂ ⁺丰度降低到220 km以下。 OH ⁺的增加导致 O ₂ ⁺丰度增加到该高度以上。每个高度的离子浓度由H ₂混合比的选择决定。

[27] In this and remaining subsections, the ion composition is listed in percent ranging from the simulation where the lower limit of a sensitivity parameter was used to the simulation where the upper limit of a sensitivity parameter was used. The first percentage summarizes case A and the second case B at 350 km. For the photochemical-only simulations where k₁ = 0 cm³ s⁻¹ and the H₂ mixing ratio varies between 1.6 and 16 ppm at 80 km, the resulting ionospheric composition at 350 km in order of decreasing abundance is OH⁺ (27–36%), O₂⁺ (30–25%), H⁺ (30–11%), H₃⁺ (2–24%), O⁺ (7–0.5%), H₂⁺ (~1%), HCO⁺ (~1%), N₂H⁺, and others are each <1%.
[27]在本小节和其余小节中，离子成分以百分比形式列出，范围从使用灵敏度参数下限的模拟到使用灵敏度参数上限的模拟。第一个百分比总结了情况 A 和第二个情况 B 在 350 公里处的情况。对于纯光化学模拟，其中k ₁ = 0 cm ³ s ⁻¹且 H ₂混合比在 80 km 处变化在 1.6 和 16 ppm 之间，所得的 350 km 处电离层成分按丰度递减顺序为 OH ⁺ (27– 36%)、O ₂ ⁺ (30–25%)、H ⁺ (30–11%)、H ₃ ⁺ (2–24%)、O ⁺ (7–0.5%)、H ₂ ⁺ (~1%)、HCO ⁺ (~1%)、N ₂ H ⁺等均<1%。

3.1.2 Sensitivity to k₁
3.1.2 对k _{1 的}敏感性

[28] The second sensitivity test studies the effects of reaction 1 in Table 2. For photochemical-only simulations, the sensitivity test for k₁ is conducted by fixing the H₂ mixing ratio at the middle value of 9 ppm at 80 km and by varying k₁ from a lower limit value of 0 to an upper limit value of 10⁻⁹ cm³ s⁻¹ (referred to as cases C and D, respectively). Figure 3 shows the results of this test for noontime conditions. Figure 3a shows the effects of varying k₁ on the electron density from lower to upper limits given by dashed to solid lines, respectively. Only the high-altitude electron density is affected by k₁, showing a small decrease with increasing reaction rate. Figure 3b shows the ion density profile ranges of ion densities, using the same format as in Figure 2. It is clear that the shading that spans the dashed and solid lines is appreciable only for a single ion (H⁺). As k₁ increases, the production rate of H₂⁺ increases (from the loss of H⁺), resulting in an increase of H₃⁺, HCO⁺, and N₂H⁺ production. Loss of H⁺ also causes a decrease in the O⁺ production. Densities of ions at lower altitudes are unaffected by the changing reaction rate due to the absence of significant concentrations of H⁺ and H₂⁺ below 200 km.
[28]第二个敏感性测试研究表2中反应1的影响。对于纯光化学模拟， k ₁的灵敏度测试是通过将H ₂混合比固定在80 km处的中间值9 ppm并将k ₁从下限值0变化到上限值10来进行的。 ^-9 cm ³ s ^-1 (分别称为情况C和D)。图3显示了中午条件下的测试结果。图3a显示了改变k ₁对电子密度的影响，从下限到上限分别由虚线到实线给出。只有高空电子密度受到k ₁的影响，随着反应速率的增加，显示出小幅下降。图3b显示了离子密度的离子密度分布范围，使用与图2中相同的格式。很明显，跨越虚线和实线的阴影仅对于单个离子 (H ⁺ ) 是明显的。随着k ₁增加，H ₂ ⁺的生成速率增加（来自H ⁺的损失），导致H ₃ ⁺ 、HCO ⁺和N ₂ H ⁺生成增加。 H ⁺的损失也会导致 O ⁺产量的减少。由于在 200 km 以下不存在显着浓度的 H ⁺和 H ₂ ^+，因此较低海拔处的离子密度不受反应速率变化的影响。

[29] For this simulation, with an H₂ mixing ratio of 9 ppm at 80 km and k₁ varying between 0 and 10⁻⁹ cm³ s⁻¹, the resulting ionospheric composition at 350 km in order of decreasing abundance is OH⁺ (34–37%), O₂⁺ (30–36%), H₃⁺ (16–22%), H⁺ (16–0.7%), H₂⁺ (~1%), HCO⁺ (~1%), and O⁺ (~1%), N₂H⁺ and others are each <1%. As in the previous subsection, the percentages range from the simulation where the lower limit of k₁ was used (case C) to the simulation where the upper limit of k₁ was used (case D).
[29]对于该模拟，在 80 km 处 H ₂混合比为 9 ppm， k ₁在 0 到 10 ^-9 cm ³ s ^-1之间变化，所得的 350 km 处电离层成分（按丰度递减顺序）为 OH ⁺ (34–37%)、O ₂ ⁺ (30–36%)、H ₃ ⁺ (16–22%)、H ⁺ (16–0.7%)、 H ₂ ⁺ (～1%)、HCO ⁺ (～1%)、O ⁺ (～1%)、N ₂ H ⁺等均<1%。与上一小节一样，百分比范围从使用k ₁下限的模拟（情况 C）到使用k ₁上限的模拟（情况 D）。

3.2 Effects on Photochemistry with Vertical Transport
3.2 垂直传输对光化学的影响

[30] Having assessed the effects that hydrogen chemistry can cause upon the plasma constituents throughout the ionosphere, the next set of simulations addresses the influence of coupled chemistry and plasma transport. Previous studies have shown that plasma diffusion becomes important in the topside ionosphere, and thus, a more comprehensive treatment of plasma dynamics is used.
[30]在评估了氢化学对整个电离层等离子体成分的影响后，下一组模拟解决了耦合化学和等离子体传输的影响。先前的研究表明，等离子体扩散在顶部电离层中变得很重要，因此，需要对等离子体动力学进行更全面的处理。

3.2.1 Sensitivity to H₂
3.2.1 对H _{2 的}敏感性

[31] A similar test is done as for the photochemical-only case by now allowing ions to diffuse vertically. Figure 4 shows the effects of varying H₂ while keeping k₁ fixed at 0, referred to as cases E and F. Figure 4a gives the electron density concentrations varying between the dashed and solid black lines as the H₂ volume mixing ratio is varied from lower to upper limits of 0 and 16 ppm, respectively. Figure 4b shows the ion density profile ranges with shaded regions of ion densities, bounded by the dashed and solid lines that correspond to these low and high limits of H₂.
[31]对于仅光化学的情况进行了类似的测试，现在允许离子垂直扩散。图4显示了在保持k ₁固定为 0 的同时改变 H ₂的影响，称为情况 E 和 F。图4a给出了当 H ₂体积混合比变化时，电子密度浓度在黑色虚线和黑色实线之间变化。从下限到上限分别为 0 和 16 ppm。图4b显示了离子密度分布范围，其中离子密度的阴影区域由对应于H ₂的这些下限和上限的虚线和实线界定。

[32] For this simulation, k₁ = 0 cm³ s⁻¹ and the H₂ mixing ratio varies between 1.6 and 16 ppm at 80 km. The resulting ionospheric composition at 350 km in order of decreasing abundance is HCO⁺ (24–87%), O₂⁺ (62–6%), O⁺(6–0.3%), OH⁺(2–4%), CO₂⁺(3–0.04%), and others are each <1%. The percentages range from the simulation where the lower limit of the H₂ mixing ratio was used (case E) to the simulation where the upper limit of the H₂ mixing ratio was used (case F).
[32]对于该模拟， k ₁ = 0 cm ³ s ^-1并且H ₂混合比在80 km时在1.6和16 ppm之间变化。由此产生的 350 km 处电离层组成按丰度递减顺序为 HCO ⁺ (24–87%)、O ₂ ⁺ (62–6%)、O ⁺ (6–0.3%)、OH ⁺ (2–4%)、 CO ₂ ⁺ (3–0.04%)，其他均<1%。百分比范围从使用H ₂混合比的下限的模拟(情况E)到使用H ₂混合比的上限的模拟(情况F)。

3.2.2 Sensitivity to k₁
3.2.2 对k _{1 的}敏感性

[33] The case of keeping H₂ at a fixed volume mixing ratio of 9 ppm and varying k₁ from 0 to 10⁻⁹ cm³ s⁻¹ and including vertical transport is shown in Figure 5. These simulations are referred to as cases G and H, respectively. The ionospheric composition varies by few ions per cubic centimeter, and the overall electron density for each limiting case is the same as is shown in Figure 5a. The ionospheric composition variation is limited to HCO⁺, O₂⁺, and H⁺ densities.
[33]将H ₂保持在9ppm的固定体积混合比并且将k ₁从0变化到10 ^-9 cm ³ s ^-1并包括垂直传输的情况如图5所示。这些模拟分别称为情况 G 和 H。电离层组成每立方厘米有几个离子变化，每个极限情况的总电子密度与图5a所示相同。电离层成分变化仅限于HCO ⁺ 、O ₂ ⁺和H ⁺密度。

[34] For this simulation, the H₂ mixing ratio is 9 ppm at 80 km, and k₁ varies between 0 and 10⁻⁹ cm³ s⁻¹. The resulting ionospheric composition at 350 km in order of decreasing abundance is shown in Figure 5b as O₂⁺ (57%), HCO⁺ (30%), OH⁺ (4%), O⁺ (2%), HCO₂⁺ (2%), N₂H⁺ (1%), and CO₂⁺ (1%), and others are each <1%. The percentages range from the simulation where the lower limit of k₁ was used (case G) to the simulation where the upper limit of k₁ was used (case H). Variability in the major ionospheric composition due to lower and upper limits of k₁ in this case is negligible.
[34]对于该模拟，80 km处的H ₂混合比为9 ppm， k ₁在0和10 ^-9 cm ³ s ^-1之间变化。由此产生的 350 km 处电离层组成（按丰度递减顺序）如图5b所示：O ₂ ⁺ (57%)、HCO ⁺ (30%)、OH ⁺ (4%)、O ⁺ (2%)、HCO ₂ ⁺ (2%)、N ₂ H ⁺ (1%)、CO ₂ ⁺ (1%)等均＜1%。百分比范围从使用k ₁下限的模拟（情况G）到使用k ₁上限的模拟（情况H）。在这种情况下，由于k ₁的下限和上限引起的主要电离层组成的变化可以忽略不计。

3.3 Effects of Ion-Ion Collisions
3.3 离子-离子碰撞的影响

[35] Models of planetary ionospheres often incorporate ion-ion collisions into the equations of motion (e.g., Chen and Nagy [1978] for Venus; Millward et al. [1996] for Earth; Moore et al. [2004] for Saturn). The model used here was adapted from Mendillo et al. [2011] that incorporated ion-neutral collisions only. Including ion-ion interactions into the model slows down ion diffusion and leads to larger ion and electron densities when compared with the case of ion-neutral interactions only. The overall increase in electron density at 400 km is 15–75%, varying with choice of H₂ mixing ratio at 80 km and k₁ reaction rate used. In Figure 6, the effects of including ion-ion collisions in the ionosphere of Mars is demonstrated for the case of H₂ mixing ratio of 16 ppm at 80 km and k₁ of 0 cm³ s⁻¹ (case F).
[35]行星电离层模型通常将离子-离子碰撞纳入运动方程（例如， Chen 和 Nagy [ 1978 ] 对于金星； Millward 等人[ 1996 ] 对于地球； Moore 等人[ 2004 ] 对于土星） 。这里使用的模型改编自Mendillo 等人。 [ 2011 ]仅包含离子中性碰撞。与仅离子-中性相互作用的情况相比，将离子-离子相互作用纳入模型会减慢离子扩散，并导致更大的离子和电子密度。 400 km 时电子密度的总体增加为 15-75%，随 80 km 时 H ₂混合比的选择和所使用的k ₁反应速率而变化。在图6中，对于在80km处H ₂混合比为16ppm且k ₁为0cm ³ s ^-1的情况(情况F)，证明了在火星电离层中包括离子-离子碰撞的效果。

4 Discussion  4 讨论

[37] The modeled HCO⁺ concentrations form a significant fraction of the Martian ionosphere. HCO⁺ is the third most abundant species below ~180 km after O₂⁺ and CO₂⁺. Above 180 km, HCO⁺ is second to and sometimes more abundant than O₂⁺.
[37]模拟的 HCO ⁺浓度构成了火星电离层的很大一部分。 HCO ⁺是~180 km 以下第三丰富的物种，仅次于 O ₂ ⁺和 CO ₂ ⁺ 。在180公里以上，HCO ^{+ 的}含量仅次于O ₂ + ，有时甚至比O 2 ⁺更丰富。

[38] It is worth noting that the Viking Lander RPA instrument required a priori assumptions of the species being measured in order to model the measured number densities of these species [Nier et al., 1972; Hanson et al., 1977]. Best fits were achieved with the assumptions that combinations of O₂⁺, CO₂⁺, and O⁺ were the dominant ions between 130 and 220 km. The RPA data do not exclude the presence of HCO⁺ (29 amu mass species potentially obscured by 32 amu O₂⁺) or OH⁺ (17 amu mass species potentially obscured by 16 amu O⁺). HCO⁺ was also predicted to be an abundant ion by Krasnopolsky [2002]. Although Fox [2003] studied the effects of hydrogen on the ionosphere, the chemical scheme used did not include HCO⁺.
[38]值得注意的是，Viking Lander RPA 仪器需要对所测量的物种进行先验假设，以便对这些物种的测量数量密度进行建模 [ Nier 等人， 1972 年；汉森等人， 1977 ]。假设 O ₂ ⁺ 、CO ₂ ⁺和 O ⁺的组合是 130 至 220 km 之间的主要离子，即可实现最佳拟合。 RPA 数据不排除 HCO ⁺ （29 amu 质量物质可能被 32 amu O ₂ ⁺掩盖）或 OH ⁺ （17 amu 质量物质可能被 16 amu O ⁺掩盖）的存在。 Krasnopolsky [ 2002 ] 也预测 HCO ⁺是一种丰富的离子。尽管Fox [ 2003 ] 研究了氢对电离层的影响，但所使用的化学方案不包括 HCO ⁺ 。

[39] The abundance of radio occultation profiles retrieved from MGS and MEX has allowed a detailed validation of the electron density concentration as a function of altitude for the model described here [Martinis et al., 2003; Mendillo et al., 2011; Lollo et al., 2012]. However, there are only two Viking Lander measurements of ion concentration at Mars.
[39]从 MGS 和 MEX 检索到的大量射电掩星剖面可以对此处描述的模型的电子密度浓度作为海拔函数进行详细验证 [ Martinis 等人， 2003 年；门迪洛等人， 2011 ； Lollo 等人， 2012 年]。然而，维京着陆器只有两次对火星离子浓度​​的测量。

[40] The ionospheric densities resulting from the simulations done for this work have been validated with the ion density profiles measured by the Viking1 Lander in Figure 7. RPA measurements of O₂⁺, O⁺, and CO₂⁺ from Hanson et al. [1977] were used for comparison with model cases A, B, E and F described in Figures 2 and 4 that show ion density variability due to H₂. An additional ion density profile for the sum of O₂⁺ and HCO⁺ is also shown for comparison. This is to account for any RPA measurements that could have resulted from Martian HCO⁺ being recorded as O₂⁺. In Figure 7a, the ion densities modeled for a lower limit of H₂ mixing ratio agree well with measurements for altitudes between 130 and 270 km for O₂⁺ (and O₂⁺ added to HCO⁺), for altitudes between 130 and 220 km for CO₂⁺ and at all altitudes for O⁺. Below 130 km, our modeled ion concentrations fall off with a similar shape to those measured by the RPA. The differences between model results and measurements below the main peak are attributed to the differences between the neutral atmosphere adopted in our model and that measured by Viking. Plasma dynamics that are not included in this simulation are likely responsible for the underestimation of modeled CO₂⁺ and overestimation of modeled O₂⁺ (despite agreement with O⁺) when compared with Viking 1 ion measurements at top altitudes. In Figure 7b, the simulation that includes vertical plasma transport (from Figure 4) is validated against the measurements. The agreement between the model and RPA measurements improves for CO₂⁺ at all altitudes and for O₂⁺ at the top side, while the model O⁺ concentrations intermittently underestimate measurements by at most a factor of 2.
[40]这项工作的模拟所产生的电离层密度已通过图7中 Viking1 着陆器测量的离子密度分布进行了验证。 Hanson 等人对 O ₂ ⁺ 、O ⁺和 CO ₂ ⁺进行 RPA 测量。 [ 1977 ] 用于与图2和图 4中描述的模型案例 A、B、E 和 F 进行比较，这些模型显示了 H ₂引起的离子密度变化。还显示了 O ₂ ⁺和 HCO ⁺总和的附加离子密度分布以进行比较。这是为了解释可能由火星 HCO ⁺记录为 O ₂ ⁺产生的任何 RPA 测量结果。在图7a中，针对 H ₂混合比下限建模的离子密度与海拔 130 至 270 km 之间的 O ₂ ⁺ （以及添加到 HCO ⁺的 O ₂ ⁺ ）、海拔 130 至 220 之间的测量结果非常吻合。公里（CO ₂ ^+）和所有海拔高度（O ^+） 。在 130 公里以下，我们模拟的离子浓度下降的形状与 RPA 测量的相似。模型结果与主峰以下测量结果之间的差异归因于我们模型中采用的中性大气与 Viking 测量的中性大气之间的差异。 与最高海拔的 Viking 1 离子测量相比，未包含在该模拟中的等离子体动力学可能是导致模型 CO ₂ ⁺低估和 O ₂ ⁺模型高估的原因（尽管与 O ⁺一致）。在图7b中，根据测量结果验证了包括垂直等离子体传输（来自图4 ）的模拟。对于所有高度的 CO ₂ ⁺和顶侧的 O ₂ ⁺ ，模型和 RPA 测量值之间的一致性有所提高，而模型 O ⁺浓度间歇性地低估测量值最多 2 倍。

[41] Due to the scarcity of measurements available at Mars of ion concentration with altitude, further comparison can only be done with other models. A summary of ion densities at a common altitude of 200–220 km is done in Table 4. The case shown in Figure 2 for photochemistry only with a lower limit of k₁ provides a good comparison to the model developed and discussed in Krasnopolsky [2002] for the solar minimum scenario. In his model, the charge exchange reaction k₁ is not considered (consistent with the lower limit in this work of k₁ = 0), H₂ has a mixing ratio at 80 km of 15 ppm (close to the upper limit in this work of 16 ppm), and at 300 km H₂ reaches a value that is close to the lower limit considered here. Chen et al. [1978] and Fox [2003] also provide models with some hydrogenated ions to compare the present results with.
[41]由于火星上离子浓度随海拔高度的测量缺乏，只能与其他模型进行进一步比较。表4总结了 200-220 km 常见高度的离子密度。图2所示的仅具有k ₁下限的光化学情况与Krasnopolsky [ 2002 ] 中针对太阳极小期情景开发和讨论的模型提供了良好的比较。在他的模型中，没有考虑电荷交换反应k ₁ （与本文中k ₁ = 0的下限一致），H ₂在80 km处的混合比为15 ppm（接近于本文中的上限） 16 ppm），并且在 300 km 时 H ₂达到接近此处考虑的下限的值。陈等人。 [ 1978 ]和Fox [ 2003 ]还提供了一些氢化离子的模型来与目前的结果进行比较。

[42] As summarized in Figure 7 and Table 4, the results of the model used for this work compare well with in situ measurements and some other models. Disagreement with remaining models is attributed to the different set of photochemical reactions and reaction rates used in different simulations. For example, in this model, OH⁺ is a major ion at upper altitudes. In a model by Krasnopolsky [2002], OH⁺ is nearly an order of magnitude less abundant at similar altitudes for the same solar cycle conditions. A comparison of production and loss mechanisms between the model used here and that detailed in Krasnopolsky [2002] shows that the latter model does not include the production reaction between H₃⁺ and O that produces much of the OH⁺ at the topside ionosphere.
[42]如图7和表4所示，本工作所用模型的结果与现场测量和其他一些模型的结果非常吻合。与其余模型的分歧归因于不同模拟中使用的不同的光化学反应和反应速率。例如，在此模型中，OH ⁺是高海拔地区的主要离子。在Krasnopolsky [ 2002 ] 的模型中，在相同的太阳周期条件下，在相似的海拔高度，OH ^{+ 的}丰富度几乎要低一个数量级。此处使用的模型与Krasnopolsky [ 2002 ] 中详述的模型之间的产生和损失机制的比较表明，后一个模型不包括 H ₃ ⁺和 O 之间的产生反应，该反应在顶部电离层产生大量 OH ⁺ 。

[43] Similar reasons explain the difference in HCO⁺ densities between the two models. HCO⁺ is produced as a secondary ion and can be generated through 10 channels listed in Table 2. The two main production mechanisms are due to CO₂⁺ reacting with H and to N₂H⁺ reacting with CO. Loss of HCO⁺ occurs exclusively through recombination at a rate proportional to T_e⁻¹, much slower than the recombination rate of most other molecular ions. This leads to the gradual buildup of HCO⁺ to large densities before reaching photochemical equilibrium. Krasnopolsky's model includes seven production reactions (four of which overlap with the model here) and a recombination rate similar to the one included in this work. Despite the differences in neutral and ion chemistry between Krasnopolsky [2002] and this work, both models project HCO⁺ to be one of the most abundant ions below 200 km.
[43]类似的原因解释了两个模型之间 HCO ⁺密度的差异。 HCO ⁺作为二次离子产生，可以通过表2中列出的 10 个通道产生。两种主要的生产机制是由于 CO ₂ ⁺与 H 反应以及 N ₂ H ⁺与 CO 反应。 HCO ⁺的损失仅通过以与T _e ^{-1 成}比例的速率重组而发生，比大多数物质的重组速率慢得多。其他分子离子。这导致 HCO ⁺在达到光化学平衡之前逐渐积累到较大的密度。 Krasnopolsky 的模型包括七个生产反应（其中四个与此处的模型重叠）和与本工作中包含的重组率类似的重组率。尽管Krasnopolsky [ 2002 ] 和这项工作之间的中性和离子化学存在差异，但这两个模型都预测 HCO ⁺是 200 km 以下最丰富的离子之一。

[44] The inclusion of H, H₂, and associated hydrogenated ions in this model has resulted in the formation of an ionosphere that is no longer exclusively dominated by O₂⁺ or O⁺ at upper altitudes. For the photochemical-only case, the various sensitivity tests shown in this work yield an ionosphere that is dominated at 350 km by comparable densities of OH⁺, O₂⁺, H₃⁺, H⁺, and smaller quantities of O⁺, HCO⁺, H₂⁺, and N₂H⁺. In the case of full vertical plasma transport, O₂⁺ and HCO⁺ dominate at 350 km with smaller quantities of O⁺, OH⁺, and HCO₂⁺.
[44]该模型中包含的 H、H ₂和相关氢化离子导致电离层的形成，该电离层不再完全由高海拔地区的 O ₂ ⁺或 O ⁺主导。对于仅光化学的情况，本工作中显示的各种灵敏度测试产生的电离层在 350 km 处由相当密度的 OH ⁺ 、O ₂ ⁺ 、H ₃ ⁺ 、H ⁺和少量的 O ⁺ 、HCO 主导。 ⁺ 、H ₂ ⁺和N ₂ H ⁺ 。在完全垂直等离子体传输的情况下，O ₂ ⁺和HCO ⁺在350 km处占主导地位，O ⁺ 、OH ⁺和HCO ₂ ⁺的数量较少。

[45] Transport of ions becomes important above ~150 km. In transitioning from the photochemistry only to the photochemistry with vertical transport case, OH⁺, H₃⁺, and H⁺ no longer dominate the ionosphere at 350 km because they have diffused downward, while both O₂⁺ and HCO⁺ have diffused upwards, resulting in the latter ions becoming a major ion species at top altitudes. The lighter ions diffuse downward and the heavier ions upward due to the dominating ion pressure term in the velocity calculations [Banks and Kockarts, 1973]. Due to chemistry, the ion density profiles of H⁺, H₂⁺, H₃⁺, and OH⁺ increase with altitude as is shown in Figures 2b, 3b, 4b, and 5b. The resulting gradient in ion density with altitude (and consequently ion pressure) dictates the velocity direction, causing the lighter hydrogenated ions to diffuse to lower altitudes. The remaining ion abundances decrease with altitude, resulting in a negative density gradient and an upward velocity that dominates over the downward velocity from the gravity term, causing these ions to be transported to higher altitudes.
[45]超过~150公里时离子传输变得重要。从仅光化学过渡到具有垂直传输情况的光化学时，OH ⁺ 、H ₃ ⁺和 H ⁺不再在 350 km 处的电离层中占主导地位，因为它们已向下扩散，而 O ₂ ⁺和 HCO ⁺均已向上扩散，导致后一种离子成为最高海拔的主要离子种类。由于速度计算中离子压力项占主导地位，较轻的离子向下扩散，较重的离子向上扩散[ Banks and Kockarts , 1973 ]。由于化学原因，H ⁺ 、H ₂ ⁺ 、H ₃ ⁺和 OH ⁺的离子密度分布随着海拔高度的增加而增加，如图2b 、 3b 、 4b和5b所示。由此产生的离子密度随高度的梯度（以及因此离子压力）决定了速度方向，导致较轻的氢化离子扩散到较低的高度。剩余的离子丰度随着高度的增加而减少，导致负密度梯度和向上的速度超过重力项的向下的速度，导致这些离子被输送到更高的高度。

5 Conclusion  5 结论

[46] A 1-D model of the Martian ionosphere [Mendillo et al., 2011], updated to include hydrogen chemistry and ion-ion collisions, shows that the composition of the topside ionosphere is very sensitive to the choice of neutral molecular hydrogen density, and less sensitive to the charge exchange reaction rate between H⁺ and H₂. Figure 8 and Table 3 summarize the major ions that dominate the ionosphere above 250 km for the different simulations presented in this study.
[46]火星电离层的一维模型 [ Mendillo et al ., 2011 ]，更新为包括氢化学和离子-离子碰撞，表明顶部电离层的组成对中性分子氢的选择非常敏感密度，对H ⁺和H ₂之间的电荷交换反应速率不太敏感。图8和表3总结了本研究中不同模拟中 250 km 以上电离层的主要离子。

[47] In the case of photochemistry only, the resulting dominant ions at 350 km are a combination of OH⁺, O₂⁺, H₃⁺, and H⁺ and smaller quantities of O⁺, HCO⁺, H₂⁺, and N₂H⁺. For the case of vertical transport, the resulting dominant ions at 350 km are O₂⁺ and HCO⁺ with smaller quantities of O⁺, OH⁺, and HCO₂⁺. Ionospheric compositions at 250 and 300 km are further summarized in Table 3. Figures 2-5 show the detailed ionospheric composition for cases of the model that demonstrate sensitivity to uncertainties in H₂ neutral density and to the rate of a charge exchange reaction between H⁺ and H₂. The neutral density uncertainty has a larger impact on ionospheric composition than the reaction rate uncertainty. In all cases discussed in this paper, hydrogenated ions play a prominent role in the composition of the upper ionosphere of Mars.
[47]仅在光化学的情况下，在 350 km 处产生的主要离子是 OH ⁺ 、O ₂ ⁺ 、H ₃ ⁺和 H ⁺以及少量 O ⁺ 、HCO ⁺ 、H ₂ ⁺和N ₂ H ⁺ 。对于垂直传输的情况，在 350 km 处产生的主要离子是 O ₂ ⁺和 HCO ⁺以及少量的 O ⁺ 、OH ⁺和 HCO ₂ ⁺ 。表3进一步总结了 250 公里和 300 公里处的电离层成分。图2 - 5显示了该模型案例的详细电离层组成，该模型展示了对 H ₂中性密度的不确定性以及对 H ⁺和 H ₂之间的电荷交换反应速率的敏感性。中性密度不确定性对电离层组成的影响比反应速率不确定性更大。在本文讨论的所有情况下，氢化离子在火星上电离层的组成中发挥着重要作用。

[48] The results shown in this work are modeled for high-latitude locations at solar minimum noontime conditions. This model can be used in future work to investigate the diurnal and seasonal variability of the topside ionospheric composition, as well as to study the effects of solar cycle variability and varying magnetic field morphologies. A hint of the role of magnetic field (B) morphology possibly emerges from these simulations. Yet, the accurate portrayal of such effects is beyond the capability of a 1-D model.
[48]这项工作中显示的结果是针对太阳最小正午条件下的高纬度地区进行建模的。该模型可在未来的工作中用于研究上部电离层成分的昼夜和季节变化，以及研究太阳周期变化和变化的磁场形态的影响。这些模拟可能暗示了磁场 (B) 形态的作用。然而，对此类效应的准确描述超出了一维模型的能力。

[49] The MAVEN mission will carry a set of instruments for studying atmospheric escape on Mars. The Neutral Gas and Ion Mass Spectrometer (NGIMS) instrument is capable of measuring and identifying the composition of thermal ions with masses ranging between 2 and 150 amu in situ at altitudes above 120 km. The resolution of the NGIMS is 1 amu, allowing measurements of HCO⁺ (29 amu) to be distinguished from similar mass ions such as O₂⁺ (32 amu) and N₂⁺ (28 amu) [M. Benna, 2012, personal communication]. Its observations will test the predictions of this work and provide constraints for future modeling efforts.
[49] MAVEN 任务将携带一套用于研究火星大气逃逸的仪器。中性气体离子质谱仪（NGIMS）仪器能够在120公里以上的原位测量和识别质量范围在2至150 amu之间的热离子的成分。 NGIMS 的分辨率为 1 amu，允许将 HCO ⁺ (29 amu) 的测量与类似质量离子（例如 O ₂ ⁺ (32 amu) 和 N ₂ ⁺ (28 amu)）区分开来 [ M. Benna ，2012 年，个人沟通]。其观察结果将测试这项工作的预测，并为未来的建模工作提供约束。

[50] The ion densities generated in this work can offer an initial context for MAVEN NGIMS measurements between 150 and 400 km (depending on the height of the region separating ionospheric plasma from solar wind plasma at the time of measurement) and can therefore aid in the investigation of chemical and dynamical processes governing the upper atmosphere and ionosphere of Mars. These, in turn, offer insights to the escape rates of various atmospheric constituents.
[50]这项工作中生成的离子密度可以为 150 到 400 km 之间的 MAVEN NGIMS 测量提供初始背景（取决于测量时电离层等离子体与太阳风等离子体之间的区域高度），因此可以帮助研究控制火星高层大气和电离层的化学和动力学过程。这些反过来又提供了对各种大气成分的逃逸率的见解。