Barotropic Instability during Eyewall Replacement
Barotropic Instability during Eyewall Replacement
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DOI：
10.3390/meteorology2020013
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发表时间：
2023-04
期刊：
影响因子：
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通讯作者：
C. Slocum;Richard K. Taft;J. Kossin;W. Schubert
中科院分区：
文献类型：
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作者：
C. Slocum;Richard K. Taft;J. Kossin;W. Schubert
就在登陆波多黎各之前，飓风玛丽亚（2017年）经历了一个同心眼墙循环，其中外部对流环看起来很强大，而内环首先扭曲成椭圆形，然后解体。目前的工作提供了进一步的支持，简单的解释，这一事件的非辐散正压模式，作为基础的线性稳定性分析和非线性数值模拟。对于线性稳定性分析，模型的轴对称基本状态涡量分布在五个区域是分段均匀的：眼，内眼壁，护城河，外眼壁和远场。这种结构的稳定性进行了研究，通过解决一个简单的特征值/特征向量问题，在不稳定的情况下，非线性演变成一个更稳定的结构模拟使用非线性正压模式。确定了三种类型的不稳定和涡度重排：（1）穿过增强涡度外环的不稳定;（2）穿过低涡度护城河的不稳定;和（3）穿过增强涡度内环的不稳定。当增强涡度环足够窄时，就会发生第一种和第三种不稳定性，非线性混合会导致涡度环更宽、更弱。第二种类型的不稳定性与飓风玛丽亚最为相关，当护城河的径向范围足够窄，以至于主眼壁的外缘和次眼壁的内缘之间发生不稳定的相互作用时，就会发生这种不稳定性。这种类型的不稳定的非线性动力学扭曲的内眼壁成一个椭圆分裂，后来重组，导致涡度三极。这种类型的不稳定性可能发生在同心眼壁循环的末期。
Just before making landfall in Puerto Rico, Hurricane Maria (2017) underwent a concentric eyewall cycle in which the outer convective ring appeared robust while the inner ring first distorted into an ellipse and then disintegrated. The present work offers further support for the simple interpretation of this event in terms of the non-divergent barotropic model, which serves as the basis for a linear stability analysis and for non-linear numerical simulations. For the linear stability analysis the model’s axisymmetric basic state vorticity distribution is piece-wise uniform in five regions: the eye, the inner eyewall, the moat, the outer eyewall, and the far field. The stability of such structures is investigated by solving a simple eigenvalue/eigenvector problem and, in the case of instability, the non-linear evolution into a more stable structure is simulated using the non-linear barotropic model. Three types of instability and vorticity rearrangement are identified: (1) instability across the outer ring of enhanced vorticity; (2) instability across the low vorticity moat; and (3) instability across the inner ring of enhanced vorticity. The first and third types of instability occur when the rings of enhanced vorticity are sufficiently narrow, with non-linear mixing resulting in broader and weaker vorticity rings. The second type of instability, most relevant to Hurricane Maria, occurs when the radial extent of the moat is sufficiently narrow that unstable interactions occur between the outer edge of the primary eyewall and the inner edge of the secondary eyewall. The non-linear dynamics of this type of instability distort the inner eyewall into an ellipse that splits and later recombines, resulting in a vorticity tripole. This type of instability may occur near the end of a concentric eyewall cycle.