Scrambling and Reorientation of Classical Atmospheric Boundary Layer Turbulence in Hurricane Winds

Abstract

The societal, economic, and ecosystem consequences of hurricanes are projected to increase with ocean warming. Although wind gusts can be highly destructive in these extreme events, current knowledge on hurricane turbulence structures is limited due to insufficient measurement sampling data and the low resolution (1–5 km) of weather models. To bridge this knowledge gap, we propose and validate a numerical approach based on a novel theoretical framework that enables us to simulate hurricane boundary layer (BL) at ≈25 m resolution. Our high‐resolution simulations revealed an intermediate layer in the hurricane BL in which the streamwise‐elongated coherent turbulence structures that typically populate the BL flows are broken into smaller eddies. The distinctive structure of turbulence in cyclonic winds also alters internal BL dynamics during hurricane landfalls by reorienting the roll vortices. We demonstrate that the centrifugal forces in hurricanes cause scrambling and reorientation of the elongated conventional atmospheric BL streaks.

Characterizing the Impacts of Turbulence Closures on Real Hurricane Forecasts: A Comprehensive Joint Assessment of Grid Resolution, Horizontal Turbulence Models, and Horizontal Mixing Length

“…One of the major drawbacks of horizontal turbulence models in WRF is the implementation of the horizontal mixing length scale, which does not consider the physics of the flow such as the strong rotation in hurricanes. Our simulations showed that decreasing the default horizontal mixing length scale in ARW significantly improves the intensity forecasts of the considered real hurricane cases. This confirms our hypothesis based on previous studies that showed the characteristic horizontal eddy size in hurricane BLs should be smaller than typical ABLs (Momen et al., 2021; Zhang, 2010) since strong rotation in hurricane flows suppresses turbulence production. Furthermore, decreasing the default L h led to enhanced vertical profiles of radial and tangential winds and extreme wind predictions in Hurricane Katrina simulations when compared to the GPS dropsonde data. Reducing the default horizontal mixing length strengthens the hurricane vortex, results in lower hurricane center SLP, and decreases the radius of maximum wind.…”

“…If we model a hurricane using a circulating Rankine vortex flow, the background vorticity will be typically larger than the local shear vorticity and thus the turbulence is expected to be suppressed in such flows. Furthermore, previous numerical and observations studies (Momen et al., 2021; Zhang, 2010; Zhang & Montgomery, 2012) showed that the energy‐containing turbulent eddy sizes in hurricane BLs are smaller than regular ABLs which indicates their suppression by strong rotation in hurricanes. Building upon these studies, we found and demonstrated that one of the major deficiencies of the existing turbulence models is their overestimated horizontal mixing length for real hurricane forecasts.…”

“…Recent numerical (Momen et al., 2021) and observational studies (Zhang, 2010; Zhang & Montgomery, 2012) have shown that the size of the most energetic turbulent eddies in hurricane BLs are smaller than in typical ABLs due to the strong rotations in hurricanes. Based on these findings, we hypothesize that the mixing length scale in hurricanes should be reduced compared to typical ABLs to improve the accuracy of hurricane forecasts.…”

“…Horizontal diffusion has been shown to be the most controlling factor for simulating maximum TC intensity (Bryan & Rotunno, 2009; Rotunno & Bryan, 2012). Furthermore, a shift of power spectrum toward higher wave numbers in hurricane systems compared to the typical ABL flows is observed both in measurements (Zhang, 2010) and high‐resolution large‐eddy simulations (Momen et al., 2021; Worsnop et al., 2017), indicating the stark difference of horizontal turbulence structures in hurricanes compared to conventional ABLs.…”

Baroclinicity in stable atmospheric boundary layers: Characterizing turbulence structures and collapsing wind profiles via reduced models and large‐eddy simulations

“…Note that the employed LES algorithm has been widely used to develop wall‐layer models (Hultmark et al ., 2013; Yang et al ., 2016) and a series of algebraic SGS closure models for the bulk of turbulent flows (Meneveau et al ., 1996; Porté‐Agel et al ., 2000). The code has also been extensively validated against many observations, for example, for neutral, unstable and stable ABLs (Bou‐Zeid et al ., 2005; Kumar et al ., 2010; Huang and Bou‐Zeid, 2013), the diurnal evolution of the ABL (Kumar et al ., 2006; 2010; Sharma et al ., 2017), scalar transport (Chamecki et al ., 2009), and hurricane BLs over the Atlantic Ocean (Momen et al ., 2021). In the current article, only the prescribed surface heat flux and baroclinicity are altered without any fundamental changes in the code's solver.…”