Thermal infrared observations of the condensing Martian polar caps: CO2 ice temperatures and radiative budget
Thermal infrared observations of the condensing Martian polar caps: CO2 ice temperatures and radiative budget
复制标题
凝结的火星极冠的热红外观测：二氧化碳冰温和辐射预算
DOI：
10.1029/96je01077
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发表时间：
1996
影响因子：
--
通讯作者：
J. Pollack
中科院分区：
文献类型：
--
作者：
F. Forget;J. Pollack
控制火星季节性极冠形成的物理过程尚未完全了解。一方面，气候模型再现了极地帽冷凝造成的大气压力的年度变化，表明冬季极地地区实际捕获的CO量低于简单能量平衡考虑的预期。另一方面，现有的航天器对冷凝极冠的观测是复杂和令人困惑的。它们的特点是高度可变的低排放区，表现出令人讨厌的冷亮度温度。为了更好地理解这些结果，我们仔细地重新分析了维京海盗红外热成像仪（IRTM）在极夜期间在两个半球获得的测量。首先，通过去除数据中低排放区的特征，我们检索了极冠的实际表面温度。我们发现，它们都低于CO的霜点的地形通常用于模式中的极地地区，特别是在南极地区。然而，我们的分析表明，低排放区在北方半球更频繁、更强烈。它们强烈地改变了这里计算和分析的极地辐射收支，从而改变了CO凝结速率。我们的结论是，模型的倾向，高估了在极冠冷凝的CO冰的量是由不同的原因在每个半球解释。在北方，模式没有模拟低排放区，低估了沙尘暴期间平流输送到极冠地区的热量，特别是高层大气极地变暖。在南部，他们高估了极冠表面温度，也没有模拟低排放区。
The physical processes that control the formation of the Martian seasonal polar caps are not completely understood. On the one hand, climate models reproducing the annual variations in atmospheric pressure caused by the condensation of the polar caps have shown that the amount of CO actually trapped in the polar regions in winter is lower than expected from simple energy balance considerations. On the other hand, the available spacecraft observations of the condensing polar caps are complex and puzzling. They are characterized by highly variable low-emission zones exhibiting anomalously cold brightness temperatures. To better understand these results, we have carefully reanalyzed the Viking infrared thermal mapper (IRTM) measurements obtained during the polar night in both hemispheres. First, by removing the signature of the low-emission zones in the data, we have retrieved the actual surface temperatures of the polar caps. We find that they were lower than the frost point of CO for the topography of the polar regions usually used in models, especially in the south polar region. However, our analysis reveals that the low-emission zones were more frequent and more intense in the northern hemisphere. They strongly altered the polar radiative budget which is computed and analyzed here, and thus the CO condensation rate. We conclude that the models' tendency to overestimate the amount of CO ice condensing in the polar caps is explained by different causes in each hemisphere. In the north, the models did not simulate the low-emission zones and underestimated the heat advected to the polar cap region during the dust storms, especially by the upper atmosphere polar warming. In the south, they overestimated the polar cap surface temperatures and also did not simulate the low-emission zones.