Baroclinic instability on hot extrasolar planets Baroclinic instability on extrasolar planets
Baroclinic instability on hot extrasolar planets Baroclinic instability on extrasolar planets
复制标题
热太阳系外行星上的斜压不稳定性 太阳系外行星上的斜压不稳定性
DOI：
10.1111/j.1365-2966.2012.21312.x
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发表时间：
2012
影响因子：
4.8
通讯作者：
Polichtchouk I
中科院分区：
文献类型：
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作者：
Polichtchouk I
我们研究了与热系外行星相关的流动条件中的斜压不稳定性。这种不稳定性对于热量的传递和混合以及影响行星上的大尺度变率都很重要。同时进行了线性正态分析和非线性初值计算，重点是自由演化的绝热情况。利用解决传统原始方程的高分辨率大气环流模型（GCM），我们表明，在当前的热系外巨行星的GCM模拟中观测到的大规模喷流可能是气压临床不稳定的，在几到几十个行星旋转的时间尺度上，产生驱动天气系统的气旋和反气旋。线性分析得到的最不稳定模态的增长率和规模与全非线性计算结果是定性的。一般来说，不稳定的喷流的演变取决于它们的标志（向东或向西），由于喷流曲率标志的变化。对于位于赤道或赤道附近的喷流来说，侧翼的不稳定性很强，而核心则不然。关键是，在低分辨率和/或高人工粘度的模拟中，不稳定性要么很差，要么根本没有被捕获。因此，在过去对热系外行星的循环研究中，没有观察到或强调这种不稳定性。
We investigate baroclinic instability in flow conditions relevant to hot extrasolar planets. The instability is important for transporting and mixing heat, as well as for influencing large-scale variability on the planets. Both linear normal mode analysis and non-linear initial-value calculations are carried out — focusing on the freely-evolving, adiabatic situation. Using a high-resolution general circulation model (GCM) which solves the traditional primitive equations, we show that large-scale jets similar to those observed in current GCM simulations of hot extrasolar giant planets are likely to be baroclinically unstable, on a timescale of a few to a few tens of planetary rotations, generating cyclones and anticyclones that drive weather systems. The growth rate and scale of the most unstable mode obtained in the linear analysis are in qualitative, good agreement with the full non-linear calculations. In general, unstable jets evolve differently depending on their signs (eastward or westward), due to the change in sign of the jet curvature. For jets located at or near the equator, instability is strong at the flanks — but not at the core. Crucially, the instability is either poorly or not at all captured in simulations with low resolution and/or high artificial viscosity. Hence, the instability has not been observed or emphasized in past circulation studies of hot extrasolar planets.