Long-term Variations of Venus’s 365 nm Albedo Observed by Venus Express, Akatsuki, MESSENGER, and the Hubble Space Telescope
Long-term Variations of Venus’s 365 nm Albedo Observed by Venus Express, Akatsuki, MESSENGER, and the Hubble Space Telescope
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DOI：
10.3847/1538-3881/ab3120
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发表时间：
2019-07
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通讯作者：
Yeon Joo Lee;K. Jessup;S. Pérez-Hoyos;D. Titov;S. Lebonnois;J. Peralta;T. Horinouchi;T. Imamura
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文献类型：
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作者：
Yeon Joo Lee;K. Jessup;S. Pérez-Hoyos;D. Titov;S. Lebonnois;J. Peralta;T. Horinouchi;T. Imamura
金星云顶附近的未知吸收体产生了从紫外线到可见光的广泛吸收特征，峰值在360 nm左右，因此在太阳能量吸收中起着关键作用。基于对金星快车和赤崎紫外线图像以及哈勃太空望远镜和信使紫外光谱数据的分析，我们定量研究了365 nm处云反照率的变化及其对金星太阳加热率的影响；在这一分析中，金星快车(金星监测相机)的UV图像的定标校正因子相对于哈勃和信使的反照率测量而更新。我们的结果表明，从2006年到2017年，整个地球上365 nm的反照率变化了2倍，根据我们的辐射传输计算，导致低纬太阳加热率变化了25%-40%。因此，在这段时间里，云层顶层的大气应该经历了相当大的太阳加热变化。我们的全球环流模式计算表明，这种变化的太阳加热率可以解释2006-2017年间观测到的纬向风的变化。长期紫外线反照率的时间尺度与太阳活动变化的重叠，使得太阳极端紫外线强度和宇宙射线变化影响了观测到的反照率趋势是可信的。反照率的变化也可能与上层云SO2气体丰度的时间变化有关，这影响了H_2SO_4-H_2O气溶胶的形成。
An unknown absorber near the cloud-top level of Venus generates a broad absorption feature from the ultraviolet (UV) to visible, peaking around 360 nm, and therefore plays a critical role in the solar energy absorption. We present a quantitative study of the variability of the cloud albedo at 365 nm and its impact on Venus’s solar heating rates based on an analysis of Venus Express and Akatsuki UV images and Hubble Space Telescope and MESSENGER UV spectral data; in this analysis, the calibration correction factor of the UV images of Venus Express (Venus Monitoring Camera) is updated relative to the Hubble and MESSENGER albedo measurements. Our results indicate that the 365 nm albedo varied by a factor of 2 from 2006 to 2017 over the entire planet, producing a 25%–40% change in the low-latitude solar heating rate according to our radiative transfer calculations. Thus, the cloud-top level atmosphere should have experienced considerable solar heating variations over this period. Our global circulation model calculations show that this variable solar heating rate may explain the observed variations of zonal wind from 2006 to 2017. Overlaps in the timescale of the long-term UV albedo and the solar activity variations make it plausible that solar extreme UV intensity and cosmic-ray variations influenced the observed albedo trends. The albedo variations might also be linked with temporal variations of the upper cloud SO2 gas abundance, which affects the H2SO4–H2O aerosol formation.