Jet Sets
Jet Sets
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喷气式飞机
DOI：
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发表时间：
2002
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通讯作者：
G. P. Williams
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作者：
G. P. Williams
为了扩大已知环流的范围并检验现有理论，研究了有关厚、薄和过渡大气层中流动动力学的各种问题。循环是使用受简单加热函数影响的原始方程模型以数字方式产生的。为了将运动限制在较薄的上层，选择加热来产生具有指数 (EXP) 垂直结构的流动，或在高处线性 (LIN) 结构但消失在下方的流动。创建了五组解决方案来定义这两种结构的地球和木星轴对称状态、一些基本的地球状态以及过渡木星状态。轴对称情况检查表面阻力、静态稳定性、旋转速率和层厚度如何影响流动特性。标准理论被扩展以允许更弱的阻力，并且解决方案证实，在较低的速率下，哈德利单元变得更宽，并且热锋变得更加尖锐和加倍。在没有任何阻力的情况下，细胞消失，热风在全球盛行。但在缺乏背景静态稳定性的情况下，细胞变得更加密集并创建自己的稳定温度场。对于正常参数值，随着旋转速率的增加，哈德利环流环流遵循理论形式，除非它们的宽度低于 3 纬度。此外，当加热层很薄并且射流被限制在高处时，细胞会产生垂直双峰振幅，同时保持深度并表现出通常的宽度。基本的 3-D 陆地案例检查了加热速率、静态稳定性、表面阻力和旋转速率对流动特性的作用。平均射流存在于有限的纬度范围内，其位置既取决于加热幅度，也取决于加热分布。当背景静态稳定性不存在时，标准环流理论变得不那么有效，因为细胞和斜压不稳定性变得更加强烈，并共同作用以稳定低纬度和中纬度。然而，当阻力减小时，由于射流较强的正压成分的抑制，斜压不稳定性变得更弱，并且限制在较低水平。其他形式的斜压不稳定性可以通过增加旋转速率或在低纬度地区添加额外的斜压源来产生双射流。过渡木星案例研究了当 LIN 和 EXP 结构的活性层在厚薄之间变化时，多个喷流如何表现。在所有情况下，喷流宽度随纬度保持恒定，但其幅度有所不同，在低纬度或中纬度达到峰值，具体取决于斜压性的分布方式。低纬度地区额外的斜压性会产生一股急流，其正压不稳定性可以驱动赤道超级旋转，无论层厚如何。涡流驱动喷流对于所有层厚度都具有相似的动力学，但与稳定的 LIN 喷流不同，EXP 喷流也会向赤道迁移，并且在极少数情况下会向极地迁移。
To broaden the range of known circulations and to test existing theory, a variety of issues are examined concerning the dynamics of flows in thick, thin, and transitional atmospheric layers. The circulations are produced numerically using a primitive equation model subject to simple heating functions. To confine the motions to a thin upper layer, the heating is chosen to produce a flow with either an exponential (EXP) vertical structure, or one that is linear (LIN) aloft while vanishing below. Five sets of solutions are created to define the terrestrial and jovian axisymmetric states, some basic terrestrial states, and the transitional jovian states for the two structures. The axisymmetric cases examine how the surface drag, static stability, rotation rate, and layer thickness influence the flow character. The standard theory is extended to allow for a weaker drag and the solutions confirm that at lower rates the Hadley cells become wider, and the thermal fronts sharper and double. In the absence of any drag, the cells disappear and a thermal wind prevails globally. But in the absence of a background static stability, the cells become more intense and create their own stable temperature field. For normal parameter values, the Hadley cells adhere to the theoretical form as the rotation rate increases, except when their width falls below 3 of latitude. Furthermore, when the heated layer is thin and the jets are confined aloft, the cells develop vertically bimodal amplitudes, while remaining deep and exhibiting the usual widths. The basic 3-D terrestrial cases examine the role of the heating rate, static stability, surface drag, and rotation rate on the flow character. The mean jets exist within a limited latitudinal range, with their location being as much dependent on the heating amplitude as on the heating distribution. When the background static stability is absent, the standard circulation theory becomes less valid as the cells and baroclinic instability become more intense and act together to stabilize low and middle latitudes. However, when the drag is reduced, the baroclinic instability becomes much weaker and confined to lower levels because of suppression by the jet’s stronger barotropic component. Other forms of baroclinic instability can be produced by creating double-jet flows, either by increasing the rotation rate or by adding an extra source of baroclinicity in low latitudes. The transitional jovian cases examine how the multiple jets behave as the active layer is varied between thick and thin for the LIN and EXP structures. In all cases, the jet widths remain constant with latitude, but their amplitudes vary, peaking either in low or middle latitudes depending on how the baroclinicity is distributed. An extra baroclinicity in low latitudes produces a jet whose barotropic instability can drive an equatorial superrotation, regardless of layer thickness. The eddy-driven jets have a similar dynamics for all layer thicknesses but, unlike the steady LIN jets, the EXP jets also migrate equatorward and, on rare occasions, poleward.