An Observational Study of Secondary Eyewall Structure in Hurricane Ivan (2004)

Eyewall Replacement Cycle (ERC) is a subject of interest in the hurricane community due to complicated processes associated with structural and intensity changes during an ERC and the difficulty to forecast the ERC event. This study analyzes Doppler radar and flight-level data from NOAA’s P-3 aircraft to investigate the evolution of the structure of Hurricane Ivan during an ERC. Ivan was well sampled by the P3 aircraft during an ERC starting on Sept. 12^th and ending on the 14^th. During this ERC event, Ivan was under moderate environmental wind shear. This study documents details of both the axisymmetric and shear-relative structure of Ivan during the ERC.

Axisymmetric structure analysis revealed expanded tangential wind field, enhanced inflow, and clear maximum in reflectivity and vertical motion during the secondary eyewall formation. Results support the presence of a mesoscale descending inflow (MDI) in the upshear left quadrant of the storm during the ERC of Ivan, upwind of enhanced precipitation in the upshear half. In addition, the secondary tangential wind maxima were present in the upshear right quadrant, downwind of the upshear rainband. The more upshear positioning of the MDI relative to the shear direction in Ivan compared to previous literature suggests that more analyses of this feature should be conducted in more ERC events.