Topographical and Local Time Dependence of Large Stationary Gravity Waves Observed at the Cloud Top of Venus
Topographical and Local Time Dependence of Large Stationary Gravity Waves Observed at the Cloud Top of Venus
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DOI：
10.1002/2017gl075792
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发表时间：
2017-12-28
影响因子：
5.2
通讯作者：
Nakamura, M.
中科院分区：
文献类型：
--
作者：
Kouyama, T.;Imamura, T.;Nakamura, M.
2015 年 Akatsuki 首次观测序列期间发现了大型静止重力波的存在。在这项研究中，报告了在 1.5 年期间的亮温图像中进一步检测到大型静止重力波。当当地下午时，这些波浪大多周期性地出现在低纬度四个特定高地地区的上方。当波的位置越过晚间界线后，波的振幅就会衰减，并且波的位置在其一生中往往会缓慢地向东漂移。驻波的出现不仅取决于表面地形，还与纬度和当地时间有关，这表明白天的太阳加热和受太阳加热影响的大气结构可能控制驻波的激发和传播。通俗摘要日本金星卫星“晓”多次发现南北长度的大型大气波，有时在金星云顶高度可达10,000公里以上（高度约70公里）。这些波多次出现在低纬度的金星高地上空，例如阿芙罗狄蒂泰拉（Aphrodite Terra）。有趣的是，从中午到晚上，每当经过高地时，海浪就会出现，而且变得更加清晰。因此，它们可以被视为日常金星现象。尽管云顶层的西向风速达到100ms(-1)（称为大气超旋转），但大波的东西向传播速度几乎为零，并且波保持在其初始位置（静止）上方。这意味着波浪的起源可能是下面的高原地形。由于波可以通过传播传输能量，驻波可以将大气能量从低层大气传输到云顶，并可能影响超自转的速度。大驻波的存在和规律出现表明金星上层和下层大气之间通过波传播不断相互作用，这为金星大气提供了一个新的视角。
The existence of large stationary gravity waves was discovered during Akatsuki's first observation sequence in 2015. In this study, the further detection of large stationary gravity waves in brightness temperature images over a 1.5year period is reported. The waves periodically appeared mostly above four specific highland regions in the low latitudes when these regions were in the local afternoon. The wave amplitudes attenuated after the wave locations passed beyond the evening terminator, and the locations of the waves tended to slowly drift eastward over their lifetimes. The appearances of stationary waves depend not only on surface topography but also on latitude and local time, suggesting that solar heating during the daytime and atmospheric structure affected by solar heating may control the excitation and propagation of stationary waves.Plain Language Summary The Japanese Venus satellite Akatsuki has repeatedly found large atmospheric waves with north-south lengths, which sometimes reach more than 10,000km at the cloud top level on Venus (altitude similar to 70 km). These waves have repeatedly appeared above the Venusian highlands in low latitudes, such as Aphrodite Terra. Interestingly, the waves appeared and became clearer each time the highlands passed from noon to evening; therefore, they can be regarded as daily Venusian phenomena. Despite westward wind speeds reaching 100ms(-1) at the cloud top level (known as atmospheric superrotation), the east-west propagation speeds of the large waves were nearly zero, and the waves stayed above their initial locations (stationary). This means that the origin of the waves could be the highland terrains below. Because waves can transport energy via propagation, stationary waves may transport atmospheric energy from the lower atmosphere to the cloud top level and may affect the speed of the superrotation. The existence and regular appearance of the large stationary waves indicate a continuous interaction between the lower and upper atmospheres on Venus via wave propagation, which provides a novel perspective of the Venusian atmosphere.