高倾角行星上的湿平流层
Wetter Stratospheres on High Obliquity Planets
摘要：
利用三维大气环流模式研究了平流层湿度对平流层湿度的影响，发现即使在全球年平均地面温度相同的情况下，高平流层湿度比低平流层湿度高3个数量级以上。三个复杂性，只存在于高的相似性被发现是因果相关的。1)高湿度下的季节变化导致极高的地面温度在极地日出现，使最终可能进入平流层的极地空气变湿。2)与低湿度情况下冷阱有效地冻结出水蒸气不同，高湿度平流层的大部分水分输入来自高纬度，因此在很大程度上绕过了冷阱。3)高湿度的气候往往比低湿度的气候温暖，从而使整个大气层湿润。我们发现，上述每个因素都可以显着增加平流层湿度。这些结果表明，对于类地系外行星，如果行星处于高湿度下，则更有可能从表面蒸发中检测到水。水逃逸可能会导致一个高湿度的行星在失控的温室发生之前失去可居住性。
英文摘要：
We investigate how obliquity affects stratospheric humidity using a 3D general circulation model and find the stratosphere under high obliquity could be over 3 orders of magnitude moister than under the low obliquity equivalent, even with the same global annual mean surface temperature. Three complexities that only exist under high obliquity are found to be causally relevant. 1) Seasonal variation under high obliquity causes extremely high surface temperatures to occur during polar days, moistening the polar air that may eventually enter the stratosphere. 2) Unlike the low obliquity scenario where the cold trap efficiently freezes out water vapor, the high obliquity stratosphere gets most of its moisture input from high latitudes, and thus largely bypasses the cold trap. 3) A high obliquity climate tends to be warmer than its low obliquity equivalent, thus moistening the atmosphere as a whole. We found each of the above factors could significantly increase stratospheric humidity. These results indicate that, for an earth-like exoplanet, it is more likely to detect water from surface evaporation if the planet is under high obliquity. The water escape could cause a high obliquity planet to loss habitability before the runaway greenhouse takes place.
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