The generation of zonal jets by large-scale mixing
The generation of zonal jets by large-scale mixing
复制标题
通过大规模混合产生层状射流
DOI：
10.1063/1.4771991
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发表时间：
2012
影响因子：
4.6
通讯作者：
A. Tissier
中科院分区：
文献类型：
--
作者：
R. K. Scott;A. Tissier
本文用一系列数值积分方法研究了中纬s面上时变地形强迫作用下纬向气流的发展，其中强迫作用集中在大尺度上，而没有通常的二维逆能量级联。在小尺度强迫的情况下，位涡的混合主要是通过小尺度涡的作用发生的，在这种情况下，位涡的混合主要发生在纬度局部Rossby波临界层区域，其宽度不断增长的时间，由于夹带的背景流体。我们发现，位涡在纬度上呈单调的分段常数阶梯状分布，只要满足比例，其中是通常的莱茵尺度，Lf是强迫尺度;这可以看作是对最近得到的条件的补充，其中Le=（e/s ~ 3）~（1/5），e是能量输入率[R. K. Scott和D. G. Dritschel，“The structure of zonal jets in geostrophic turbulence，”J. Fluid Mech.711，576-598（2012）10.1017/jfm.2012.410]对于小尺度强迫的情况。数值结果进一步表明，位涡混合的性质是控制的比例Le/Lf主要发生在临界层时Le/Lf？1/6.因此，阶梯形成的组合条件可以表示为。最后，在一组单独的实验中，它表明，当强迫是由一个添加剂源项在演化方程中表示，是常见的做法，在二维湍流的数值调查，非守恒的位涡的影响可能会掩盖发展的楼梯轮廓在临界层混合为主的制度。© 2012美国物理研究所。
The development of zonal flows on a midlatitude s-plane subject to a time-varying topographic forcing is investigated in a series of numerical integrations in which the forcing is concentrated at large scalesin which the usual two-dimensional inverse energy cascade is absent. In contrast to the case of small-scale forcing, where mixing of potential vorticity occurs largely through the action of small-scale eddies, mixing of potential vorticity in this case occurs predominantly in latitudinally localized Rossby wave critical layer regions, whose width grows continuously in time due to the entrainment of background fluid. The potential vorticity is found to organize into a piecewise constant staircase-like profile, monotonic in latitude, provided the ratio , where is the usual Rhines scale and Lf is the scale of the forcing; this may be regarded as supplemental to the condition , where Le=(e/s3)1/5 and eis the rate of energy input, obtained recently [R. K. Scott and D. G. Dritschel, "The structure of zonal jets in geostrophic turbulence," J. Fluid Mech.711, 576-598 (2012)10.1017/jfm.2012.410] for the case of small-scale forcing. The numerical results further suggest that the nature of the potential vorticity mixing is controlled by the ratio Le/Lfoccurs predominantly in critical layers when Le/Lf ? 1/6. A combined condition for staircase formation may therefore be expressed as . Finally, in a separate set of experiments it is shown that when forcing is represented by an additive source term in the evolution equation, as is common practice in numerical investigations of two-dimensional turbulence, the effect of non-conservation of potential vorticity may obscure the development of the staircase profile in the critical layer mixing dominated regime. © 2012 American Institute of Physics.