Structure of mesovortices in Hurricane Ike (2008) derived from dual-Doppler analyses from ground-based radars

Past modeling work has shown that vorticity mixing in the tropical cyclone (TC) inner core can lead to mesovortices (MVs) and impact storm intensity. Observations of MVs are necessary to improve understanding of these features and their role in TC dynamics, but few have been made. This study presents nearly 10 hr of observation of MVs in the inner eyewall of Hurricane Ike (2008) prior to and during landfall. For the duration of landfall, the University of Alabama in Huntsville's Mobile Alabama X-band dual-polarization Doppler radar (MAX) was deployed at the Anahuac airport, about 53 km to the NE of the Houston/Galveston National Weather Service NEXRAD 88D, allowing for true dual-Doppler sampling. Dual-Doppler derived vertical vorticity, divergence, perturbation pressure, horizontal and vertical wind fields are analyzed over the landfall time period. All but two of the 16 investigated possible MV features are deemed MVs, that is, the entities contain distinct local vorticity peaks. Results indicate persistent arrangements in kinematic fields that degrade as the hurricane progresses inland. For the 14 confirmed MVs, largest local vertical vorticity values are on the order of 8.0 x 10^-3 s^-1 to 8.5 x 10^-3 s^-1, and average maximum upward vertical motion values are on the order of 10 m s^-1. Perturbation pressure retrievals suggest a local pressure perturbation minimum of 2.5-3 hPa associated with mature MVs. As the entities progress around the eye, the preferential updraft location transitions around the vorticity center in a manner consistent with the conceptual model proposed by Braun et al. 2006 based on their high-resolution simulation of Hurricane Bonnie (1998). Characteristics shown for the MVs in Ike compare well with the limited body of previous MV observational work, including the cases of Hurricanes Hugo (1989) and Isabel (2003).