Investigating Convective Scale Variability in Tropical Cyclone Rainband Clouds and Dynamics using Compact Raman Lidar Measurements

The confluence of heavy rainfall, strong winds, and elevated storm surge makes tropical cyclone (TC) rainbands an extreme risk to coastal communities. To better prepare for damaging TC landfall events, properly diagnosing small scale rainband structure is essential. Just as importantly, a better understanding of the rainbands will help predict TC structural evolution over the life span of the system. While models of this region’s dynamics have recently improved, high resolution measurements of the TC rainbands remain sparse. Particularly, spatially variable rainband convection is poorly identified by current aircraft radar methods, which rely on large precipitation particles to diagnose cloud structure. In this study, compact Raman lidar (CRL) cloud and thermodynamic measurements identify convective and stratiform clouds in TC rainbands. The CRL was deployed on NOAA’s P-3 aircraft, and its backscattered power channel differentiates between clouds and rainfall, allowing for the accurate depiction of rainband clouds below flight level. CRL data are supplemented by existing radar measurements, allowing for quantitative comparisons with a verified dataset.

This analysis highlights how novel CRL measurements depict TC rainband clouds with unprecedented detail. Instead of uniform convective or stratiform regions, the CRL identifies convective plumes interspersed between rainy and clear air regions within rainbands. These observations show how the development of rainband convection is often asymmetric and is initiated through processes unique to different TC intensities. Since the CRL captures accurate cloud heights up to flight height, the calculation of convective plume width variability is possible.

Additionally, in the clear air regions between deep rainband convection, CRL temperature and water vapor measurements highlight the presence of warm, dry air masses at mid-levels that act to cap convective growth. These findings are consistent with previous studies on inwardly advected parcels of low equivalent potential temperature air from the rainbands, which hinder TC intensification. Case studies of Category 1 and 4 TCs are presented using all available observational data to tie observed cloud heights to thermodynamics. The interaction between rainband convection and the generation of warm, dry air at low levels is a topic of particular focus. This analysis highlights the necessity of using CRL data to diagnose small scale rainband structures, and these results further improve our understanding of this impactful TC region.