Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations
Dayside cloud top structure of Venus retrieved from Akatsuki IR2 observations
复制标题
从 Akatsuki IR2 观测中检索到的金星白天云顶结构
DOI：
10.1016/j.icarus.2020.113682
复制
发表时间：
2020
期刊：
影响因子：
3.2
通讯作者：
Nakamura M.
中科院分区：
文献类型：
--
作者：
Sato T.M.;Satoh T.;Sagawa H.;Manago N.;Lee Y.J.;Murakami S.;Ogohara K.;Hashimoto G.L.;Kasaba Y.;Yamazaki A.;Yamada M.;Watanabe S.;Imamura T.;Nakamura M.
2016年4月4日至5月25日，我们利用金星轨道飞行器赤月号（Akatsuki）上的2 μm相机（IR2）的2.02 μm通道，从各种太阳相位角（0-120°）拍摄的93幅图像中检索到金星的日侧云顶结构。由于2.02 μm通道位于co2吸收带，金星反射的太阳光使我们能够确定2.02 μm单位气溶胶光学深度对应的云顶高度。首先，利用观测到的太阳相位角依赖关系和赤道方向30°区域反射太阳光的中心到边缘变化，构建了以云顶高度为70.4 km、2模态半径rg、2和云标高度th为特征的空间平均云顶结构。其次，每个地点的云顶高度是逐像素检索的，假设整个地球的云顶高度是均匀的。云顶高度的纬向结构相对赤道是对称的。赤道地区平均云顶高度为70.5 km，在纬度45°处逐渐降低~2 km。在50-60°纬度迅速下降，在70-75°纬度达到61公里。赤道方向30°区域的平均云顶高度对当地时间的依赖可以忽略不计，变化最大可达1 km。云顶高度的局部变化，包括静止重力波特征，发生在几百米以内。虽然向极~45°方向的长带状或倾斜条纹特征可以清晰地识别，但中低纬度地区的特征通常不明显。这些并不一定表现为云顶的局部变化，在云顶观察到斑驳的紫外模式，暗示了云顶的对流和湍流。
We describe the dayside cloud top structure of Venus as retrieved from 93 images acquired at a wide variety of solar phase angles (0–120°) using the 2.02-μm channel of the 2-μm camera (IR2) onboard the Venus orbiter, Akatsuki, from April 4 to May 25, 2016. Since the 2.02-μm channel is located in a CO2absorption band, the sunlight reflected from Venus allowed us to determine the cloud top altitude corresponding to unit aerosol optical depth at 2.02 μm. First, the observed solar phase angle dependence and the center-to-limb variation of the reflected sunlight in the region equatorward of 30° were used to construct a spatially averaged cloud top structure characterized by cloud top altitudezc, Mode 2 modal radiusrg,2, and cloud scale heightH, which were 70.4 km, 1.06 μm, and 5.3 km, respectively. Second, cloud top altitudes at individual locations were retrieved on a pixel-by-pixel basis with an assumption thatrg,2andHwere uniform for the entire planet. The latitudinal structure of the cloud top altitude was symmetric with respect to the equator. The average cloud top altitude was 70.5 km in the equatorial region and showed a gradual decrease of ~2 km by the 45° latitude. It rapidly dropped at latitudes of 50–60° and reached 61 km in latitudes of 70–75°. The average cloud top altitude in the region equatorward of 30° showed negligible local time dependence, with changes up to 1 km at most. Local variations in cloud top altitude, including stationary gravity wave features, occurred within several hundreds of meters. Although long zonal or tilted streaky features poleward of ~45° were clearly identifiable, features in the low and middle latitudes were usually subtle. These did not necessarily appear as local variations at the cloud top level, where mottled and patchy UV patterns were observed, suggestive of convection and turbulence at the cloud top level.