In convective fluids, small vortices develop between neighboring convective cells. Familiar in the atmosphere in the form of dust devils and water spouts, these convective vortices have been seen in simulations of oceanic convection where the vortices exhibit an unexplained bias towards cyclonic rotation despite having a large Rossby number. Here we use large eddy simulations (LES) of an idealized oceanic convective mixed layer and vary independently the Coriolis acceleration and the surface buoyancy flux to investigate the development of the cyclonic bias of convective vortices. While large convective vortices are biased for sufficiently large values of the Coriolis parameter, small convective vortices do not exhibit a clear bias. Using Lagrangian particles, we find that the large convective vortices develop through the merger of many small convective vortices. We propose a statistical theory to predict the cyclonic bias of large convective vortices composed of many small unbiased convective vortices and test the theory using LES results. We apply the theory to typical convective conditions and find that convective vortices in upper ocean mixed layers are expected to exhibit a bias, while convective vortices in the terrestrial and Martian atmospheres are expected to be largely unbiased.

中文翻译：

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旋转系统中对流涡旋的气旋偏差模型

在对流流体中，相邻对流单元之间会形成小涡流。这些对流涡旋以尘暴和水龙卷的形式出现在大气中，在海洋对流的模拟中也出现过，尽管这些涡旋具有很大的罗斯比数，但仍表现出无法解释的气旋性旋转倾向。在这里，我们使用理想化海洋对流混合层的大涡模拟（LES），并独立变化科里奥利加速度和表面浮力通量来研究对流涡旋气旋偏差的发展。虽然大的对流涡旋有足够大的科里奥利参数值的偏差，但小的对流涡旋并没有表现出明显的偏差。利用拉格朗日粒子，我们发现大对流涡旋是通过许多小对流涡旋的合并而形成的。我们提出了一种统计理论来预测由许多小型无偏对流涡旋组成的大型对流涡旋的气旋偏差，并使用 LES 结果测试该理论。我们将该理论应用于典型的对流条件，发现上层海洋混合层中的对流涡旋预计会表现出偏差，而陆地和火星大气中的对流涡旋预计在很大程度上是无偏差的。