Changes in Jupiter's zonal velocity between 1979 and 2008
Changes in Jupiter's zonal velocity between 1979 and 2008
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DOI：
10.1016/j.icarus.2010.11.018
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发表时间：
2011-02-01
期刊：
影响因子：
3.2
通讯作者：
de Pater, Imke
中科院分区：
文献类型：
--
作者：
Asay-Davis, Xylar S.;Marcus, Philip S.;de Pater, Imke
我们发现，木星的可见云水平纬向风的峰值速度在24度N（行星）从2000年到2008年增加。这一增加是2000年至2008年纬度在+/- 70度之间的纬向速度的唯一变化，具有统计学意义，与可见天气没有明显联系。我们提出了第一个自动检索的快速（类似于130米秒（-1））纬向速度在8度N行星纬度，并表明，以前的一些检索错误地发现了较慢的纬向风，因为向东漂移的黑暗投影（关联5亩热点）“上当”检索算法。我们确定了纬向速度在2000年从卡西尼图像从美国宇航局的行星数据系统使用一个全球性的方法类似于以前的横向移动相关方法使用的其他人，以及基于二维速度场纵向平均的局部方法。我们从2008年5月哈勃太空望远镜（HST）上的宽视场行星照相机2（WFPC 2）获得的图像中获得了全球速度。纬向风的长期变化是基于与1979年旅行者2号和1995-1998年HST图像上公布的速度进行比较。在1979年的旅行者2号和1995-1998年的HST速度中发现了纬向风速在10 m s（-1）量级上的波动，时间尺度从几周到几个月不等。在间隔10小时的数据中，我们发现由于纵向波动引起的东西向速度不确定性接近10 m s（-1），因此10 m s（-1）的速度波动可能发生在甚至小于10小时的时间尺度上。如此大范围的时间尺度波动限制了纬向风测量的准确性。平均纬向速度的概念可能是不适定的，并且将“时间平均”纬向速度定义为跨越几个月或几年的几个纬向速度场的平均值可能没有物理意义。在8度N，我们使用我们的全球方法找到2000年类似于110 m s（-1）和2008年类似于130 m s（-1）的峰值纬向速度。由我们的本地和全球方法产生的2000年卡西尼数据的纬向速度在任何地方都是一致的，除了在8度N附近。在那里，本地算法表明，东西方向的速度有很大的变化，在经度;广大地区超过类似140米秒（-1）。我们的全球算法，和所有的速度提取算法中使用的先前发表的研究，发现东西漂移速度的可见的黑暗投影，而不是真正的纬向速度在可见云的水平。因此，2000年至2008年8度N纬向风的明显增加并不是纬向速度的真正变化。在7.3度N，伽利略探测器发现3巴水平的纬向速度为170 m s（-1）。如果该纬度可见云层的纬向风速近似于140 m s（-1），而不是近似于105 m s（-1），则垂直纬向风切变比目前公认的值小得多。爱思唯尔公司出版
We show that the peak velocity of Jupiter's visible-cloud-level zonal winds near 24 degrees N (planetographic) increased from 2000 to 2008. This increase was the only change in the zonal velocity from 2000 to 2008 for latitudes between +/- 70 degrees that was statistically significant and not obviously associated with visible weather. We present the first automated retrieval of fast (similar to 130 m s(-1)) zonal velocities at 8 degrees N planetographic latitude, and show that some previous retrievals incorrectly found slower zonal winds because the eastward drift of the dark projections (associated with 5-mu m hot spots) "fooled" the retrieval algorithms.We determined the zonal velocity in 2000 from Cassini images from NASA's Planetary Data System using a global method similar to previous longitude-shifting correlation methods used by others, and a new local method based on the longitudinal average of the two-dimensional velocity field. We obtained global velocities from images acquired in May 2008 with the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST). Longer-term variability of the zonal winds is based on comparisons with published velocities based on 1979 Voyager 2 and 1995-1998 HST images. Fluctuations in the zonal wind speeds on the order of 10 m s(-1) on timescales ranging from weeks to months were found in the 1979 Voyager 2 and the 1995-1998 HST velocities. In data separated by 10 h, we find that the east-west velocity uncertainty due to longitudinal fluctuations are nearly 10 m s(-1), so velocity fluctuations of 10 m s(-1) may occur on timescales that are even smaller than 10 h. Fluctuations across such a wide range of timescales limit the accuracy of zonal wind measurements. The concept of an average zonal velocity may be ill-posed, and defining a "temporal mean" zonal velocity as the average of several zonal velocity fields spanning months or years may not be physically meaningful.At 8 degrees N, we use our global method to find peak zonal velocities of similar to 110 m s(-1) in 2000 and similar to 130 m s(-1) in 2008. Zonal velocities from 2000 Cassini data produced by our local and global methods agree everywhere, except in the vicinity of 8 degrees N. There, the local algorithm shows that the east-west velocity has large variations in longitude; vast regions exceed similar to 140 m s(-1). Our global algorithm, and all of the velocity-extraction algorithms used in previously-published studies, found the east-west drift velocities of the visible dark projections, rather than the true zonal velocity at the visible-cloud level. Therefore, the apparent increase in zonal winds between 2000 and 2008 at 8 degrees N is not a true change in zonal velocity.At 7.3 degrees N, the Galileo probe found zonal velocities of 170 m s(-1) at the 3-bar level. If the true zonal velocity at the visible-cloud level at this latitude is similar to 140 m s(-1) rather than similar to 105 m s(-1), then the vertical zonal wind shear is much less than the currently accepted value. Published by Elsevier Inc.