We present our current understanding of the composition, vertical mixing, cloud structure and the origin of the atmospheres of Jupiter and Saturn. Available observations point to a much more vigorous vertical mixing in Saturn's middle-upper atmosphere than in Jupiter's. The nearly cloud-free nature of the Galileo probe entry site, a 5-micron hotspot, is consistent with the depletion of condensable volatiles to great depths, which is attributed to local meteorology. Somewhat similar depletion of water may be present in the 5-micron bright regions of Saturn also. The supersolar abundances of heavy elements, particularly C and S in Jupiter's atmosphere and C in Saturn's, as well as the progressive increase of C from Jupiter to Saturn and beyond, tend to support the icy planetesimal model of the formation of the giant planets and their atmospheres. However, much work remains to be done, especially in the area of laboratory studies, including identification of possible new microwave absorbers, and modelling, in order to resolve the controversy surrounding the large discrepancy between Jupiter's global ammonia abundance, hence the nitrogen elemental ratio, derived from the earth-based microwave observations and that inferred from the analysis of the Galileo probe-orbiter radio attenuation data for the hotspot. We look forward to the observations from Cassini-Huygens spacecraft which are expected to result not only in a rich harvest of information for Saturn, but a better understanding of the formation of the giant planets and their atmospheres when these data are combined with those that exist for Jupiter.

中文翻译：

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木星和土星大气的比较：深层大气成分、云结构、垂直混合和起源

我们介绍了我们目前对木星和土星大气的组成、垂直混合、云结构和起源的理解。现有的观测表明，土星中上层大气的垂直混合比木星的要剧烈得多。伽利略探测器入口处几乎无云的性质是一个 5 微米的热点，这与可冷凝挥发物消耗到很深的地方是一致的，这归因于当地的气象。土星的 5 微米明亮区域也可能存在类似的水枯竭现象。重元素的超太阳丰度，特别是木星大气中的 C 和 S 和土星大气中的 C，以及 C 从木星到土星及其他地方的逐渐增加，倾向于支持巨行星及其大气形成的冰星微模型。然而，还有很多工作要做，特别是在实验室研究领域，包括确定可能的新微波吸收剂和建模，以解决围绕木星全球氨丰度之间巨大差异的争议，因此氮元素比，来自地基微波观测和从伽利略探测器-轨道器无线电衰减数据分析推断出的热点。我们期待着卡西尼-惠更斯号飞船的观测，这不仅会为土星带来丰富的信息收获，