Comparative terrestrial planet thermospheres: 3. Solar cycle variation of global structure and winds at solstices
Comparative terrestrial planet thermospheres: 3. Solar cycle variation of global structure and winds at solstices
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DOI：
10.1029/1999je001232
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发表时间：
1999-07
影响因子：
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通讯作者：
S. Bougher;S. Engel;R. Roble;B. Foster
中科院分区：
文献类型：
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作者：
S. Bougher;S. Engel;R. Roble;B. Foster
使用全球数据库对行星上层大气进行比较的工作进入了一个新时代，因为最近出现了对火星热层的气动测量[例如，基廷等人，1998a]。目前成熟的建模能力也使我们能够使用全球三维模型对比地球和火星的热层结构、风和控制过程[例如，Bougher等人，1999年b]。本文利用美国国家大气研究中心的热层大气环流模式，比较了地球和火星热层的季节-太阳周期响应，以研究∼100千米以上的耦合能量、动力学和中性离子组成。预计在至日会出现极端的热层条件，从而揭示出控制地球和火星热层结构和风的基本物理过程的重要性在不断变化。火星外基面温度的季节-太阳周期极值计算在200-380K之间，产生的最大水平风速接近215-400m/S。相应的地球外基面温度的极端值在700-1600K之间，全球风的变化相当小。研究还表明，地球和火星的轨道偏心率也会导致它们的热层温度发生很大变化。对于火星来说，在太阳活动最大的情况下，从远日点到近日点，日面外基面温度变化了∼60K(18%)。如此大的温度变化强烈地影响了热层密度和全球风。相应的地球白天温度在两个至日之间也有60-80K的变化。然而，地球轨道上的温度变化百分比(5%)及其对热层结构和风的总体影响要小得多。极光活动实际上可能掩盖了这些轨道变化。整个火星年不断变化的尘埃条件调制了其低层大气的气溶胶加热，导致太阳以下电离层峰值的高度与其观测到的季节趋势(∼115-130公里)有相当大的变化。在比较地球和火星热层特征和基本过程方面取得重大进一步进展，必须等待B星和火星快车(2004-2005年)预期扩大的火星全球数据库。
The comparison of planetary upper atmospheres using global databases has entered a new era with the advent of recent aerobraking measurements of the Mars thermosphere [e.g., Keating, et al., 1998a]. The present maturity of available modeling capabilities also permits us to contrast the Earth and Mars thermosphere structures, winds, and controlling processes using global three-dimensional models [e.g., Bougher et al., 1999b]. This present effort focuses upon the comparison of the combined seasonal-solar cycle responses of the thermospheres of Earth and Mars using the National Center for Atmospheric Research (NCAR) Thermospheric General Circulation Model (TGCM) utility to address the coupled energetics, dynamics, and neutral-ion composition above ∼100 km. Extreme thermospheric conditions are expected at solstices, thereby revealing the changing importance of fundamental physical processes controlling the Earth and Mars thermospheric structures and winds. Seasonal-solar cycle extremes in Mars exobase temperatures are calculated to range from 200 to 380 K, giving rise to maximum horizontal winds of nearly 215 to 400 m/s. Corresponding extremes in Earth exobase temperatures are 700 to 1600 K, with rather small variations in global winds. The orbital eccentricities of Earth and Mars are also shown to drive substantial variations in their thermospheric temperatures. For Mars, dayside exobase temperatures vary by ∼60 K (18%) from aphelion to perihelion during solar maximum conditions. Such large temperature variations strongly impact thermospheric densities and global winds. The corresponding Earth dayside temperatures also vary by 60–80 K between solstices. However, the percent temperature variation (5%) over the Earth's orbit and its overall impact on the thermospheric structure and winds are much smaller. Auroral activity may in fact obscure these orbital variations. Changing dust conditions throughout the Martian year modulate the aerosol heating of its lower atmosphere, yielding considerable variability in the height of the subsolar ionospheric peak about its observed seasonal trend (∼115–130 km). Significant further progress in the comparison of Earth and Mars thermospheric features and underlying processes must await expanded Mars global databases expected from Planet-B and Mars Express (2004–2005).