Dylan R. Card, Kristen L. Corbosiero, and Brian Tang
Tropical cyclones pose a significant threat to life and property, and exhibit many severe weather hazards as they make landfall, such as storm surge, strong winds, flooding rains, and tornadoes. Tropical cyclone rainbands are associated with nearly all of these hazards, which can extend hundreds of kilometers inland. Thus, understanding tropical cyclone rainband structure, and the individual convective cells of which rainbands are composed, is important to mitigating risk. Several previous studies have documented the overall structure of tropical cyclone rainbands, including the cells of which they are comprised, and the environments in which they are embedded. These studies have documented the vertical structure of the principle and distant rainbands, and the thermodynamic environments in which they occur. Observational studies have noted that tropical cyclone convection tends to organize downshear and have shown rotating thunderstorms tend to occur in the northeast quadrant of the tropical cyclone. Modeling studies have shown that convective cells tend to form upshear-right and mature as the traverse cyclonically around the tropical cyclone.
This study uses the National Center for Atmospheric Research (NCAR) Real-Time Convection-Allowing Ensemble to delve into how a high-resolution ensemble system reproduces the rainband structure, and the dynamic and thermodynamic environment of hurricanes Harvey and Irma (2017). Further, an examination and verification of the bulk characteristics of the individual convective cells, which compose the principle and outer rainbands, was conducted.
The NCAR Ensemble model reflectivity areal extent tends to be larger than observed reflectivity fields. The NCAR Ensemble also produced thermodynamic environments and rainband structures in agreement with previous observational and modeling studies in both the horizontal and vertical. The rainbands of each ensemble member were very unique in terms of number of rainbands and orientation of the rainbands. Convective cells tended to be present in the rainbands, located to the right of the environmental shear vector, with most non-rotating cells in the right of shear quadrants and most rotating cells occurring directly downshear. The convection within both tropical cyclones has a strong diurnal signal with non-rotating convective cells increasing after sunrise and peak in the late afternoon. The rotating cells however did not appear to have a strong diurnal signal associated with them.
Card, D., 2019: A Multiscale Analysis of the Rainband and Cellular Structure in Hurricanes Harvey and Irma (2017) Using the NCAR Ensemble. M.S. thesis, Department of Atmospheric and Environmental Science, University at Albany.
Poster: 9th Annual Northeast Tropical Workshop
