Six years of Venus winds at the upper cloud level from UV, visible and near infrared observations from VIRTIS on Venus Express
Six years of Venus winds at the upper cloud level from UV, visible and near infrared observations from VIRTIS on Venus Express
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DOI：
10.1016/j.pss.2014.12.010
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发表时间：
2015-08-01
影响因子：
2.4
通讯作者：
Sanchez-Lavega, A.
中科院分区：
文献类型：
--
作者：
Hueso, R.;Peralta, J.;Sanchez-Lavega, A.
金星快车任务提供了对金星大气层的长期监测，包括其上层云层的形态和运动。一些工作集中在对65-70公里高度敏感的紫外图像中可见的昼侧上层云的动力学，以及在1.74 μ m光谱窗口中可见的行星夜侧低层云（50公里高度）。本文利用VIRTIS-M近波长的光谱图像，在以往VIRTIS-M数据分析的基础上，在紫外（360-400 nm）、可见光（570-680 nm）和近红外（900-955 nm）三个通道对上层云层进行了研究。紫外线图像在云顶显示出对比相对较好的云特征。可见光和近红外图像中的云特征位于云顶下方几公里处，对比度很低，与紫外线图像中的云特征截然不同。在六年的时间里，研究人员利用半自动云相关算法在覆盖南半球的118个轨道上获得了风的测量数据。VIRTIS-M紫外线数据对上层云层的分析结果证实了之前基于金星监测相机获得的图像的分析（Khatuntsev et al.(2013)）。在云顶，平均纬向风和经向风随当地时间变化，向当地下午加速。哈德利单体环流的上层分支在纬度45°和当地时间14-16 h达到最大速度。2006-2012年期间，紫外线云层的平均纬向风加速了至少15 m s（-1）。近红外和可见光图像显示一个更恒定的环流，没有明显的时间变化或纵向变化。在近红外和可见光图像中，经向环流不存在或略有逆转，这表明金星大气中的哈德利环流很浅，或者经向环流的返回分支延伸到近红外图像中探测到的云层以下的水平。在亚极至极纬度，三个波长范围表现出相似的特征和运动，这是小垂直风切变的标志，可能受到两层垂直辐合的影响。通过比较金星快车第一年（2006-2008年）和之后（2009-2012年）的纬向风观测，在UV图像观测到的云顶层有一个下午时间纬向风长期加速的特征，两个时间段的平均纬向风加速度为17 +/- 6 m s（-1）。(C) 2014 Elsevier Ltd.版权所有。
The Venus Express mission has provided a long-term monitoring of Venus atmosphere including the morphology and motions of its upper clouds. Several works have focused on the dynamics of the upper cloud visible on the day-side in ultraviolet images sensitive to the 65-70 km altitude and in the lower cloud level (50 km height) observable in the night-side of the planet in the 1.74 mu m spectral window. Here we use VIRTIS-M spectral images in nearby wavelengths to study the upper cloud layer in three channels: ultraviolet (360-400 nm), visible (570-680 nm) and near infrared (900-955 nm) extending in time the previous analysis of VIRTIS-M data. The ultraviolet images show relatively well contrasted cloud features at the cloud top. Cloud features in the visible and near infrared images lie a few kilometers below the upper cloud top, have very low contrast and are distinct to the features observed in the ultraviolet. Wind measurements were obtained on 118 orbits covering the Southern hemisphere over a six-year period and using a semi-automatic cloud correlation algorithm. Results for the upper cloud from VIRTIS-M ultraviolet data confirm previous analysis based on images obtained by the Venus Monitoring Camera (Khatuntsev et al. (2013)). At the cloud top the mean zonal and meridional winds vary with local time accelerating towards the local afternoon. The upper branch of the Hadley cell circulation reaches maximum velocities at 45 latitude and local times of 14-16 h. The mean zonal winds in the ultraviolet cloud layer accelerated in the course of the 2006-2012 period at least 15 m s(-1). The near infrared and visible images show a more constant circulation without significant time variability or longitudinal variations. The meridional circulation is absent or slightly reversed in near infrared and visible images indicating that, either the Hadley-cell circulation in Venus atmosphere is shallow, or the returning branch of the meridional circulation extends to levels below the cloud level sensed in near infrared images. At subpolar to polar latitudes the three wavelength ranges show similar features and motions which is a signature of small vertical wind shear and may be affected by vertical convergence of both layers. At the clod top level observed in UV images there are signatures of a long-term acceleration of the zonal winds at afternoon hours when comparing zonal winds from the first years of Venus Express observations (2006-2008) to later dates (2009-2012) with a mean acceleration of zonal winds of 17 +/- 6 m s(-1) between both time periods. (C) 2014 Elsevier Ltd. All rights reserved.