Latitudinal regionalization of rotating spherical shell convection
Latitudinal regionalization of rotating spherical shell convection
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DOI：
10.1017/jfm.2022.1010
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发表时间：
2022-11
影响因子：
3.7
通讯作者：
T. Gastine;J. Aurnou
中科院分区：
文献类型：
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作者：
T. Gastine;J. Aurnou
对流现象普遍存在于旋转的地球物理和天体物理体上和内部。以前的球壳研究表明，极地地区的对流动力学与低纬度的赤道动力学有很大的不同。然而，大多数球壳对流标度律使用全球平均的量，消除了物理学中的纬度差异。在这里，我们通过分析球壳模拟的区域化对流传热特性来量化这些纬度差异。这是通过测量在两个特定的，纬度上分开的，壳的部分，极地和赤道地区，$Nu_p$和$Nu_e$，分别进行本地努塞尔数。在旋转的球壳中，对流首先在切向圆柱体的外部发生，使得赤道热传递在小的和中等的超临界状态下占主导地位。我们表明，浮力强迫，参数化的瑞利数Ra$，必须超过临界赤道强迫的一个因素${\approx }20$内的切线圆柱体触发极地对流。一旦被触发，$Nu_p$随$Ra$增加的速度比$Nu_e$快得多。赤道和极地的热通量，然后往往成为可比在足够高的Ra$。极地对流数据和笛卡尔数值模拟之间的比较揭示了两种几何形状之间的定量协议的传热和平均体温度梯度。这一协议表明，旋转球壳对流动力学是通过球形模拟和通过减少蒸发途径，无论是理论，数值或实验。
Convection occurs ubiquitously on and in rotating geophysical and astrophysical bodies. Prior spherical shell studies have shown that the convection dynamics in polar regions can differ significantly from the lower latitude, equatorial dynamics. Yet most spherical shell convective scaling laws use globally-averaged quantities that erase latitudinal differences in the physics. Here we quantify those latitudinal differences by analysing spherical shell simulations in terms of their regionalized convective heat-transfer properties. This is done by measuring local Nusselt numbers in two specific, latitudinally separate, portions of the shell, the polar and the equatorial regions, $Nu_p$ and $Nu_e$ , respectively. In rotating spherical shells, convection first sets in outside the tangent cylinder such that equatorial heat transfer dominates at small and moderate supercriticalities. We show that the buoyancy forcing, parameterized by the Rayleigh number $Ra$ , must exceed the critical equatorial forcing by a factor of ${\approx }20$ to trigger polar convection within the tangent cylinder. Once triggered, $Nu_p$ increases with $Ra$ much faster than does $Nu_e$ . The equatorial and polar heat fluxes then tend to become comparable at sufficiently high $Ra$ . Comparisons between the polar convection data and Cartesian numerical simulations reveal quantitative agreement between the two geometries in terms of heat transfer and averaged bulk temperature gradient. This agreement indicates that rotating spherical shell convection dynamics is accessible both through spherical simulations and via reduced investigatory pathways, be they theoretical, numerical or experimental.