Ground‐based near‐infrared observations of the Venus nightside: 1.27‐μm O2(a 1Δ g ) airglow from the upper atmosphere
Ground‐based near‐infrared observations of the Venus nightside: 1.27‐μm O2(a 1Δ g ) airglow from the upper atmosphere
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金星夜间地面近红外观测：来自高层大气的 1.27μm O2(a 1Δ g ) 气辉
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
F. Mills
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文献类型：
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作者：
D. Crisp;V. Meadows;B. Bézard;C. Bergh;J. Maillard;F. Mills
1975年对金星进行的近红外光谱观测显示，金星的日侧和夜侧都有O2（a1Δg）气辉，发射率超过1兆瑞利（1 MR = 1012光子cm−2 s−1到4π sr）。如此高的发射率表明，在金星的白天，大部分通过CO2光解产生的氧原子最终在激发态（a1Δg）重新结合产生O2。这个结果最初是令人惊讶的，因为现有的实验室测量表明，原子氧重组反应的O2（a1Δg）产量不超过几个百分点。最近的观测揭示了更大的O2气辉强度（a1Δg）以及这种气辉在空间和时间上的巨大变化。1991年加拿大、法国、夏威夷望远镜/傅立叶变换光谱仪拍摄的金星夜侧高分辨率（0.3 cm−1）光谱显示，光谱积分O2（a1Δg）强度高达1.1 mW m−2 sr−1。一旦根据观测角度和下伏云层的反射对这些值进行校正，它们表明发射率接近3mr。这些光谱还显示发射层（90至115公里）的旋转温度为186±6k。1991年、1993年和1994年由英澳望远镜/红外成像光谱仪和加拿大、法国、夏威夷望远镜/成像傅立叶变换光谱仪拍摄的光谱图像立方体提供了对这种发射的时空变化的更完整的描述。在O2(a1Δg) q分支（1.269 μm）波长范围内提取的图像在夜侧的对比度通常大于10比1。尽管碟面平均强度与1975年的相当，但一些局部区域的气辉发射率大于5mr，最亮的发射通常局限于直径1000至2000公里的区域。这些明亮的区域在很多纬度和当地时间都能被探测到，但它们最常出现在低纬度地区和当地时间在金星午夜到凌晨3点之间。在不到一个小时的时间里，最亮的斑点的强度可以变化20%，它们可以在不到一天的时间里完全消失。这些新的观测为金星上层中间层和下层热层的大气化学和动力学模型提供了改进的约束条件。
Near-infrared spectroscopic observations of Venus taken in 1975 revealed O2(a1Δg) airglow from both the dayside and nightside of the planet with emission rates exceeding 1 mega-Rayleigh (1 MR = 1012 photons cm−2 s−1 into 4π sr). These large emission rates indicated that most of the atomic oxygen produced through the photolysis of CO2 on the dayside of Venus eventually recombined to produce O2 in the excited (a1Δg) state. This result was initially surprising because available laboratory measurements indicated O2(a1Δg) yields from atomic oxygen recombination reactions that were no larger than a few percent. More recent observations reveal even larger O2(a1Δg) airglow intensities as well as dramatic spatial and temporal variations in this airglow. High-resolution (0.3 cm−1) spectra of the Venus nightside taken with the Canada France Hawaii Telescope/Fourier transform spectrometer in 1991 show spectrally integrated O2(a1Δg) intensities as large as 1.1 mW m−2 sr−1. Once these values are corrected for viewing angle and reflection from the underlying clouds, they indicate emission rates near 3 MR. These spectra also yield rotational temperatures of 186 ± 6 K in the emitting layer (90 to 115 km). Spectral image cubes taken with the Anglo-Australian Telescope/infrared imaging spectrometer and the Canada France Hawaii Telescope/imaging Fourier transform spectrometer during 1991, 1993, and 1994 provide a more complete description of the spatial and temporal variability in this emission. Images extracted at wavelengths within the O2(a1Δg) Q-branch (1.269 μm) often show contrasts larger than 10 to 1 across the nightside. Even though the disk-averaged intensities are comparable to those seen in 1975, some localized regions have airglow emission rates larger than 5 MR. The brightest emission is often confined to 1000- to 2000-km-diameter regions. These bright regions have been detected over a broad range of latitudes and local times, but they are most often seen at low latitudes and at local times between midnight and 0300 on Venus. The intensity of the brightest spots can change by 20% in less than 1 hour, and they can vanish entirely in less than 1 day. These new observations are providing improved constraints on atmospheric chemical and dynamical models of the upper mesosphere and lower thermosphere of Venus.