天王星在春分点：云的形态和动力学
Uranus at equinox: Cloud morphology and dynamics
摘要：
随着2007年12月7日天王星春分的临近，环和大气观测者使用10米凯克望远镜和哈勃太空望远镜进行了大量的观测。我们使用2007年6月7日至2007年9月9日期间的卫星来识别和跟踪云特征，确定大气运动，描述云形态和动力学特征，并确定大气能带结构的变化。我们证实了疑似北半球急流的存在，其峰值位于58 N附近，并将风速测量扩展到73 N。对于28个云特征，我们通过延长跟踪时间获得了极高的风速精度。新的结果证实了纬向风廓线中的南北不对称性，并且在1986年（接近冬至）和2007年（接近春分）之间南半球没有任何变化，这表明这种不对称性可能是永久性的，而不是季节性的逆转。在2007年的图像中，我们发现了两组明显的离散云特征，它们的寿命非常长。30 S附近的一个已经偏离了以前的振荡运动，并开始了一个显着的向北漂移，伴随着显着的形态变化。北纬30度附近的复合特征保持在一个几乎固定的纬度上，同时表现出一些伴随着明亮同伴特征的黑点特征。在其他纬度，较小且不太稳定的特征被用来追踪云的运动，其中一些持续了许多行星旋转，但许多无法追踪到超过一次凌日。在45 N附近出现了一个亮带，而在45 S附近的亮带开始衰减，这两个事件都与天王星的不对称能带结构是对太阳强迫的延迟响应的观点一致，但延迟时间却令人惊讶地短，只有几年。
英文摘要：
As the 7 December 2007 equinox of Uranus approached, ring and atmosphere observers produced a substantial collection of observations using the 10-m Keck telescope and the Hubble Space Telescope. Those spanning the period from 7 June 2007 through 9 September 2007 we used to identify and track cloud features, determine atmospheric motions, characterize cloud morphology and dynamics, and define changes in atmospheric band structure. We confirmed the existence of the suspected northern hemisphere prograde jet, locating its peak near 58 N, and extended wind speed measurements to 73 N. For 28 cloud features we obtained extremely high wind-speed accuracy through extended tracking times. The new results confirm a small N-S asymmetry in the zonal wind profile, and the lack of any change in the southern hemisphere between 1986 (near solstice) and 2007 (near equinox) suggests that the asymmetry may be permanent rather than seasonally reversing. In the 2007 images we found two prominent groups of discrete cloud features with very long lifetimes. The one near 30 S has departed from its previous oscillatory motion and started a significant northward drift, accompanied by substantial morphological changes. The complex of features near 30 N remained at a nearly fixed latitude, while exhibiting some characteristics of a dark spot accompanied by bright companion features. Smaller and less stable features were used to track cloud motions at other latitudes, some of which lasted over many planet rotations, though many could not be tracked beyond a single transit. A bright band has developed near 45 N, while the bright band near 45 S has begun to decline, both events in agreement with the idea that the asymmetric band structure of Uranus is a delayed response to solar forcing, but with a surprisingly short delay of only a few years.
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