On Scale-Dependent Turbulent Characteristics in the Eyewall Boundary Layer of Intense Hurricanes

Turbulent transport within the hurricane boundary layer (HBL) is crucial for understanding the intensification and maintenance of hurricanes. Traditional data collection methods have often excluded the eyewall regions due to safety constraints, leaving a gap in detailed turbulence data for these critical areas. This study analyzed flight-level data collected by NOAA P-3 aircraft during eyewall penetrations of Category 5 Hurricane Hugo (1989) and Category 4 Hurricane Allen (1980) at an altitude of approximately 500 m. The wavelet technique (WT) was used to estimate turbulent kinetic energy (TKE) and momentum flux (MF) under non-stationary conditions. TKE and MF values utilizing an 8 km integration scale are nearly double those obtained using a 2 km integration scale at equivalent wind speeds. Further investigations into TKE and MF variability in relation to radial distances from the radius of maximum wind speed have shown significant discrepancies. The values of TKE and MF can change by an order of magnitude if the inner eyewall is included in the integration leg. This result highlights the challenge of selecting a leg for turbulence parameter estimation near the eyewall due to the chaotic nature of the HBL in the eyewall. This study is the first to assess the impact of integration length scales on turbulence parameters in intense eyewalls. It emphasizes the necessity of implementing scale-aware turbulent parameterizations in hurricane forecast models.