Tropical Cyclone Boundary Layer Rolls in Synthetic Aperture Radar Imagery

Abstract

Marine atmospheric boundary layer (MABL) roll plays an important role in the turbulent exchange of momentum, sensible heat, and moisture throughout MABL of tropical cyclone (TC). Hence, rolls are believed to be closely related to TC's development, intensification, and decay processes. Spaceborne synthetic aperture radar (SAR) provides a unique capability to image the sea surface imprints of quasi‐linear streaks induced by the MABL rolls within a TC. In this study, sixteen SAR images, including three images acquired during three major hurricanes: Irma, Jose, and Maria in the 2017 Atlantic hurricane season, were utilized to systematically map the distribution and wavelength of MABL rolls under the wide range of TC intensities. The images were acquired by SAR onboard RADARSAT‐1/2, ENVISAT, and SENTINEL‐1 satellites. Our findings are in agreement with the previous one case study of Hurricane Katrina (2005), showing the roll wavelengths are between 600 and 1,600 m. We also find that there exist roll imprints in eyewall and rainbands, although the boundary layer heights are shallower there. Besides, the spatial distribution of roll wavelengths is asymmetrical. The roll wavelengths are found to be the shortest around the storm center, increase and then decrease with distance from storm center, reaching the peak values in the range of d∗−2d∗, where d∗ is defined as the physical location to TC centers normalized by the radius of maximum wind. These MABL roll characteristics cannot be derived using conventional aircraft and land‐based Doppler radar observations.

An assessment of marine atmospheric boundary layer roll detection using Sentinel-1 SAR data

“…Note that multiple peaks are visible, principally associated with irregularities in the main linear features throughout the image scene. Still a dominant azimuthal peak direction is apparent and similar FFT methodologies have been used to extract the dominant orientation of MABL rolls (Gerling, 1986;Mourad and Walter, 1996;Li et al, 2013;Huang et al, 2018). depth, or contrast, is obtained after normalization by their average (σ 0…”

A direct aircraft observation of helical rolls in the tropical cyclone boundary layer

“…Of note, Huang et al 13 found that km-scale and sub-km-scale rolls coexist in the TCBL by analyzing many Synthetic Aperture Radar (SAR) images. Gall et al 14 documented large scale (~ 10 km) rolls in landfalling hurricanes.…”

Estimation of Wind Direction in Tropical Cyclones Using C-Band Dual-Polarization Synthetic Aperture Radar

“…For high winds, MABL rolls are prevalent in the TC boundary layer. The surface imprints of kilometer-scale roll vortices are clearly visible in the SAR images of hurricanes [20], [21]. In particular, 3-6-km wavelength roll vortices have been associated with secondary circulations between the main TC rain bands [1].…”