Thermal tides in the upper cloud layer of Venus as deduced from the emission angle dependence of the brightness temperature by Akatsuki/LIR
Thermal tides in the upper cloud layer of Venus as deduced from the emission angle dependence of the brightness temperature by Akatsuki/LIR
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Akatsuki/LIR 根据亮温的发射角依赖性推导出金星上云层的热潮
DOI：
10.1029/2020je006808
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Takao M. Sato
中科院分区：
文献类型：
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作者：
Masahiro Akiba;Makoto Taguchi;Tetsuya Fukuhara;Takeshi Imamura;Toru Kouyama;Takao M. Sato
由Akatsuki上的长波红外照相机（LIR）获得的金星盘的亮温显示出在低纬度和中纬度明显的临边变暗。临边亮度廓线反映了大气温度和云粒子光学厚度的垂直分布。通过对近5.8金星年LIR观测资料的水平分布分析，从发射角与探测高度的关系出发，研究了云顶亮温分布的垂直结构。根据过去的观测结果，通过标称温度和云粒子分布的辐射传输计算，将发射角转换为感测高度。我们展示了三个纬度带云顶上方亮温偏差的当地时间-高度横截面。导出的68 km以上的全日潮和半日潮垂直振幅分布基本上可以用经典的热潮理论解释。在赤道地区可以清楚地看到相位随高度向上移动的半日潮。将重力内波的频散关系应用于观测到的波结构，发现66-71公里高度的纬向平均纬向风速与已知的超旋转速度大致相同。通过比较观测和模拟的垂直位相结构，我们认为赤道云顶的潮波结构是太阳加热在上层云层中产生的重力波向上传播的一个方面。
The brightness temperature of the Venus disk obtained by Longwave Infrared Camera (LIR) on board Akatsuki shows clear limb darkening at low and middle latitudes. The profile of limb brightness reflects the vertical distributions of atmospheric temperature and the optical thickness of the cloud particles. Horizontal distributions of brightness temperature obtained by LIR during ∼5.8 Venusian years were analyzed to investigate the vertical structure of the brightness temperature distribution above the cloud tops based on the emission angle dependence of the sensing altitude. Emission angles were converted to sensing altitudes by a radiative transfer calculation with nominal temperature and cloud particle distributions based on past observations. We show a local time‐altitude cross section of the brightness temperature deviation above the cloud tops for three latitudinal zones. The derived vertical amplitude distribution of the diurnal and semidiurnal tides above ∼68 km is mostly explained by the classical theory of thermal tides. A semidiurnal tide in which the phase shifts upstream with altitude is clearly seen in the equatorial region. By applying the dispersion relation of the internal gravity wave to the observed wave structure, it was found that the zonally averaged zonal wind velocity at altitudes of 66–71 km was approximately the same as the known superrotation velocity. By comparing the observed and simulated vertical phase structures, it is suggested that the tidal wave structure seen in the equatorial cloud tops is an aspect of upward propagation of a gravity wave generated in the upper cloud layer by solar heating.