On the Applicability of Linear, Axisymmetric Dynamics in Intensifying and Mature Tropical Cyclones
On the Applicability of Linear, Axisymmetric Dynamics in Intensifying and Mature Tropical Cyclones
复制标题
线性轴对称动力学在加强和成熟热带气旋中的适用性
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
Roger K. Smith
中科院分区：
文献类型：
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作者：
M. Montgomery;Roger K. Smith
研究了线性化轴对称动力学在热带气旋增强和结构变化中的适用性。这项研究的动机是最近的一项工作，该工作提出了线性化、非流体静力、涡-非弹性运动方程（所谓的3DVPAS模型）的轴对称解。这项工作对最近提出的非线性系统尺度边界层旋转机制在增强风暴和成熟风暴中进行二次眼壁形成的重要性提出了质疑。这个问题是利用一个增强的热带气旋的三维中尺度模拟，以及线性3DVPAS模式来研究的。对于来自中尺度模拟的强加涡强迫项，线性模型的解仅在涡旋内核区域的短时间内（t < 1 h）有效。在较晚的时间，被忽略的非线性项变得重要，线性结果失效。因此，线性结果不能用于描述热带气旋后期动力学的所有方面。特别是，它们不能被用来(a)忽视非线性边界层自旋机制的重要性，也不能(b)至少在非线性边界层内将非绝热加热和摩擦的单独影响分离开来。这种分离依赖于线性叠加原理，当非线性很重要时，线性叠加原理就失效了。类似的警告适用于另一种线性模型的使用，即传统的Sawyer-Eliassen平衡模型。它的适用性不仅受到线性的限制，而且受到运动严格平衡假设的限制。两者都与非线性自旋不相容。
The applicability of linearized axisymmetric dynamics to the intensification and structure change of tropical cyclones is investigated. The study is motivated by recent work that presented axisymmetric solutions to the linearized, non-hydrostatic, vortex-anelastic equations of motion (the so-called 3DVPAS model). The work called into question the importance of a recently proposed nonlinear, system-scale boundary-layer spinup mechanism both in intensifying storms and in mature storms undergoing secondary eyewall formation. The issue is examined using a three-dimensional mesoscale simulation of an intensifying tropical cyclone, alongside the linear 3DVPAS model. Solutions to the linear model, for imposed eddy forcing terms derived from the mesoscale simulation, are shown to be valid only for short times ( t < 1 h) in the inner-core region of the vortex. At later times, the neglected nonlinear terms become significant and the linear results invalid. It follows that the linear results cannot be used to describe all aspects of the tropical cyclone dynamics at later times. In particular, they cannot be used (a) to dismiss the importance of the nonlinear boundary-layer spinup mechanism, nor (b) to isolate the separate effects of diabatic heating from those of friction, within the nonlinear boundary layer at least. Such separation depends on the linear superposition principle, which fails whenever nonlinearity is important. Similar caveats apply to the use of another linear model, the traditional Sawyer–Eliassen balance model. Its applicability is limited not only by linearity, but also by its assumption of strictly balanced motion. Both are incompatible with nonlinear spinup.