The Evolution of Asymmetries in the Tropical Cyclone Boundary Layer Wind Field during Landfall
The Evolution of Asymmetries in the Tropical Cyclone Boundary Layer Wind Field during Landfall
复制标题
热带气旋登陆期间边界层风场的不对称演化
DOI：
10.1175/mwr-d-21-0191.1
复制
发表时间：
2022
影响因子：
3.2
通讯作者：
Nolan, David S.
中科院分区：
文献类型：
--
作者：
Hlywiak, James;Nolan, David S.
本文研究了热带气旋登陆前边界层风场的演变过程。正如之前的研究所指出的，典型的海洋上的TCBL风结构特征是运动左侧的超梯度边界层射流和相对于地球的最大风在右侧。然而，风场对海岸线摩擦辐合的详细响应却鲜为人知。在这里，理想化的数值模拟显示，当TC离岸约200公里时，海上径向和垂直速度开始增加。径向速度的增加是由于高梯度气流穿过近海海岸线时摩擦应力的突然减小。次级环流增强的角动量平流迫使TCBL顶部附近的超梯度急流增强。灵敏度实验表明，海岸粗糙度的不连续性主导着运动引起的摩擦不对称性。此外，通过增加气动粗糙度长度来增加内陆粗糙度可以增强观测到的不对称性。最后，简要分析了三次墨西哥湾飓风登陆期间收集的地面风数据，并与理想模拟结果进行了比较。尽管现场数据有限，但观测结果总体上支持模拟。这里的结果表明，基于对水平均匀表面类型的观测的关于TCBL风场的假设——这在以前的研究中已经得到了很好的证明——不适用于强摩擦非均质性。
The evolution of the tropical cyclone boundary layer (TCBL) wind field before landfall is examined in this study. As noted in previous studies, a typical TCBL wind structure over the ocean features a supergradient boundary layer jet to the left of motion and Earth-relative maximum winds to the right. However, the detailed response of the wind field to frictional convergence at the coastline is less well known. Here, idealized numerical simulations reveal an increase in the offshore radial and vertical velocities beginning once the TC is roughly 200 km offshore. This increase in the radial velocity is attributed to the sudden decrease in frictional stress once the highly agradient flow crosses the offshore coastline. Enhanced advection of angular momentum by the secondary circulation forces a strengthening of the supergradient jet near the top of the TCBL. Sensitivity experiments reveal that the coastal roughness discontinuity dominates the friction asymmetry due to motion. Additionally, increasing the inland roughness through increasing the aerodynamic roughness length enhances the observed asymmetries. Last, a brief analysis of in situ surface wind data collected during the landfall of three Gulf of Mexico hurricanes is provided and compared to the idealized simulations. Despite the limited in situ data, the observations generally support the simulations. The results here imply that assumptions about the TCBL wind field based on observations from over horizontally homogeneous surface types—which have been well documented by previous studies—are inappropriate for use near strong frictional heterogeneity.