金星冷环状云结构纬向变化
Latitudinal Variation of Clouds' Structure Responsible for Venus' Cold Collar
AI总结：
本研究改进了金星GCM的辐射传输方案，考虑云结构纬向变化，成功模拟出与观测相符的冷环结构，表明云结构对冷环形成至关重要。
摘要：
全球气候模型（GCM）是理论上研究行星大气的一般动力学和特定现象的非常有用的工具。在金星的情况下，几个GCM成功再现了大气超旋转和全球温度场。然而，高度变化的极地温度和永久性冷环尚未得到满意的再现。在这里，我们改进了皮埃尔·西蒙·拉普拉斯研究所金星GCM的辐射传输方案，以数值模拟金星大气中的极地热特征。与先前模型的主要区别在于，我们现在考虑了云结构的纬向变化。太阳加热速率和红外冷却速率都已修改，以考虑云顶高度向极地降低以及不同粒子模式丰度随纬度的变化。在$2\times10^{4} - 4\times10^{3}$~Pa（$\sim62 - 66$~km）高度范围和$60^{\circ} - 90^{\circ}$纬度带中，平均温度场出现了一个与观测到的冷环非常相似的新结构。它不像基于观测的图中那样与极地隔离，但获得的温度值（220~K）与观测值吻合良好。跨越该区域的温度极地图显示了一个内部温暖区域，其中观测到极地涡旋，但获得的230~K平均值比观测平均值更冷，模拟的水平结构未显示涡旋内的精细尺度特征。我们的研究表明，云结构在冷环形成中至关重要。尽管我们的分析侧重于辐射强迫的改进及其在热结构中引起的变化，但极地动力学确实受到这种修改环境的影响，并且在冷环区域发现了显著的上涌运动。
英文摘要：
Global Climate Models (GCM) are very useful tools to study theoretically the general dynamics and specific phenomena in planetary atmospheres. In the case of Venus, several GCMs succeeded in reproducing the atmosphere's superrotation and the global temperature field. However, the highly variable polar temperature and the permanent cold collar have not been reproduced satisfactorily yet. Here we improve the radiative transfer scheme of the Institut Pierre Simon Laplace Venus GCM in order to numerically simulate the polar thermal features in Venus atmosphere. The main difference with the previous model is that we now take into account the latitudinal variation of the cloud structure. Both solar heating rates and infrared cooling rates have been modified to consider the cloud top's altitude decrease toward the poles and the variation in latitude of the different particle modes' abundances. A new structure that closely resembles the observed cold collar appears in the average temperature field at $2\times10^{4} - 4\times10^{3}$~Pa ($\sim62 - 66$~km) altitude range and $60^{\circ} - 90^{\circ}$ latitude band. It is not isolated from the pole as in the observation-based maps, but the obtained temperature values (220~K) are in good agreement with observed values. Temperature polar maps across this region show an inner warm region where the polar vortex is observed, but the obtained 230~K average value is colder than the observed mean value and the simulated horizontal structure does not show the fine-scale features present within the vortex. Our study shows that the cloud structure is essential in the cold collar formation. Although our analysis focuses on the improvement of the radiative forcing and the variations it causes in the thermal structure, polar dynamics is definitely affected by this modified environment and a noteworthy upwelling motion is found in the cold collar area.
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