Department of Mechanical Engineering, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 8410530, Israel and Nordita, Stockholm University and KTH Royal Institute of Technology, 10691 Stockholm, Sweden.
Phys Rev E. 2019 Dec;100(6-1):063101. doi: 10.1103/PhysRevE.100.063101.
We find an instability resulting in generation of large-scale vorticity in a fast-rotating small-scale turbulence or turbulent convection with inhomogeneous fluid density along the rotational axis in anelastic approximation. The large-scale instability causes excitation of two modes: (i) the mode with dominant vertical vorticity and with the mean velocity being independent of the vertical coordinate; (ii) the mode with dominant horizontal vorticity and with the mean momentum being independent of the vertical coordinate. The mode with the dominant vertical vorticity can be excited in a fast-rotating density-stratified hydrodynamic turbulence or turbulent convection. For this mode, the mean entropy is depleted inside the cyclonic vortices, while it is enhanced inside the anticyclonic vortices. The mode with the dominant horizontal vorticity can be excited only in a fast-rotating density-stratified turbulent convection. The developed theory may be relevant for explanation of an origin of large spots observed as immense storms in great planets, e.g., the Great Red Spot in Jupiter and large spots in Saturn. It may be also useful for explanation of an origin of high-latitude spots in rapidly rotating late-type stars.
我们发现，在粘弹性近似下，在快速旋转的小尺度湍流或具有非均匀流体密度沿旋转轴的湍流对流中，会出现一种不稳定性，导致大规模涡度的产生。这种大尺度不稳定性会激发两种模式：（i）主导垂直涡度且平均速度与垂直坐标无关的模式；（ii）主导水平涡度且平均动量与垂直坐标无关的模式。主导垂直涡度的模式可以在快速旋转的密度分层流体力学湍流或湍流对流中被激发。对于这种模式，在气旋涡旋内部，平均熵被消耗，而在反气旋涡旋内部，平均熵被增强。主导水平涡度的模式只能在快速旋转的密度分层湍流对流中被激发。所发展的理论可能有助于解释在大行星中观测到的巨大风暴（例如木星上的大红斑和土星上的大斑点）的起源。它也可能有助于解释快速旋转的晚型恒星的高纬斑点的起源。
