Dynamical Regimes of Polar Vortices on Terrestrial Planets with a Seasonal Cycle
Dynamical Regimes of Polar Vortices on Terrestrial Planets with a Seasonal Cycle
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DOI：
10.3847/psj/ac54b6
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发表时间：
2022-02
影响因子：
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通讯作者：
Ilai Guendelman;D. Waugh;Y. Kaspi
中科院分区：
文献类型：
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作者：
Ilai Guendelman;D. Waugh;Y. Kaspi
极涡是常见的行星尺度流动，在中纬度或高纬度地区环绕极地，在太阳系的大部分行星大气中都可以观测到。地球、火星和土卫六上的极地涡旋与平均经向环流动态相关，并表现出显着的季节周期。然而，这三颗行星的极涡特征各不相同。为了了解影响极地涡旋动力学和对行星参数的依赖性的机制，我们使用具有季节周期的理想化大气环流模型，在该模型中我们改变倾角、自转速率和轨道周期。我们发现极地涡旋季节性循环在参数空间中存在不同的规律。一些状况与观测到的极地涡旋有相似之处，包括在仲冬期间极地涡旋以缓慢的旋转速度减弱，类似于土卫六的极地涡旋。在参数空间内发现的其他区域在太阳系中没有对应的区域。此外，我们表明，对于参数空间的很大一部分，涡旋的位涡纬度结构是环形的，类似于在火星和土卫六上观测到的极地涡旋结构。我们还发现仲冬期间风暴活动受到抑制，类似于在火星和地球上观察到的抑制，这种情况发生在喷射速度特别强的模拟中。这种多种多样的极地涡旋动力学机制与观测到的极地涡旋具有相似之处，表明在系外行星中，极地涡旋可能存在很大的变化。
Polar vortices are common planetary-scale flows that encircle the pole in the middle or high latitudes and are observed in most of the solar system’s planetary atmospheres. The polar vortices on Earth, Mars, and Titan are dynamically related to the mean meridional circulation and exhibit a significant seasonal cycle. However, the polar vortex’s characteristics vary between the three planets. To understand the mechanisms that influence the polar vortex’s dynamics and dependence on planetary parameters, we use an idealized general circulation model with a seasonal cycle in which we vary the obliquity, rotation rate, and orbital period. We find that there are distinct regimes for the polar vortex seasonal cycle across the parameter space. Some regimes have similarities to the observed polar vortices, including a weakening of the polar vortex during midwinter at slow rotation rates, similar to Titan’s polar vortex. Other regimes found within the parameter space have no counterpart in the solar system. In addition, we show that for a significant fraction of the parameter space, the vortex’s potential vorticity latitudinal structure is annular, similar to the observed structure of the polar vortices on Mars and Titan. We also find a suppression of storm activity during midwinter that resembles the suppression observed on Mars and Earth, which occurs in simulations where the jet velocity is particularly strong. This wide variety of polar vortex dynamical regimes that shares similarities with observed polar vortices, suggests that among exoplanets there can be a wide variability of polar vortices.