Atmospheric circulation patterns derived from multi-spectral remote sensing can serve as a guide for choosing a suitable entry location for a future in situ probe mission to the Ice Giants. Since the Voyager-2 flybys in the 1980s, three decades of observations from ground- and space-based observatories have generated a picture of Ice Giant circulation that is complex, perplexing, and altogether unlike that seen on the Gas Giants. This review seeks to reconcile the various competing circulation patterns from an observational perspective, accounting for spatially-resolved measurements of: zonal albedo contrasts and banded appearances; cloud-tracked zonal winds; temperature and para-H 2 measurements above the condensate clouds; and equator-to-pole contrasts in condensable volatiles (methane, ammonia, and hydrogen sulphide) in the deeper troposphere. These observations identify three distinct latitude domains: an equatorial domain of deep upwelling and upper-tropospheric subsidence, potentially bounded by peaks in the retrograde zonal jet and analogous to Jovian cyclonic belts; a mid-latitude transitional domain of upper-tropospheric upwelling, vigorous cloud activity, analogous to Jovian anticyclonic zones; and a polar domain of strong subsidence, volatile depletion, and small-scale (and potentially seasonally-variable) convective activity. Taken together, the multi-wavelength observations suggest a tiered structure of stacked circulation cells (at least two in the troposphere and one in the stratosphere), potentially separated in the vertical by (i) strong molecular weight gradients associated with cloud condensation, and by (ii) transitions from a thermally-direct circulation regime at depth to a wave- and radiative-driven circulation regime at high altitude. The inferred circulation can be tested in the coming decade by 3D numerical simulations of the atmosphere, and by observations from future world-class facilities. The carrier spacecraft for any probe entry mission must ultimately carry a suite of remote-sensing instruments capable of fully constraining the atmospheric motions at the probe descent location.

中文翻译：

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冰巨环流模式：对大气探测器的影响


来自多光谱遥感的大气环流模式可以作为未来冰巨人原位探测任务选择合适进入位置的指南。自 20 世纪 80 年代航海者 2 号飞越以来，地面和天基观测站经过三十年的观测，已经生成了一幅复杂、令人费解的冰巨星环流图，完全不同于在气态巨星上看到的情况。本综述旨在从观测角度协调各种相互竞争的环流模式，并考虑以下空间分辨测量：纬向反照率对比和带状外观；云迹纬向风；凝结云上方的温度和 para-H 2 测量；对流层深层可凝结挥发物（甲烷、氨和硫化氢）的赤道与极地对比。这些观测结果确定了三个不同的纬度区域：深上升流和对流层上层沉降的赤道区域，可能以逆行纬向急流峰值为界，类似于木星气旋带；中纬度过渡区，有上层对流层上升流和云活动剧烈，类似于木星反气旋区；以及强烈沉降、挥发性消耗和小规模（且可能随季节变化）对流活动的极地区域。综合起来，多波长观测结果表明，堆叠的循环单元具有分层结构（至少两个在对流层，一个在平流层），可能在垂直方向上被（i）与云凝结相关的强分子量梯度分开，以及(ii)从深度的热直接环流状态转变为高空的波浪和辐射驱动的环流状态。 推断的环流可以在未来十年通过大气的 3D 数值模拟以及未来世界级设施的观测进行测试。任何探测器进入任务的运载航天器最终都必须携带一套能够完全限制探测器下降位置大气运动的遥感仪器。