Secondary eyewall formation in high-resolution simulations

Secondary eyewall formation (SEF) is still an important research topic in the study of tropical cyclone (TC) dynamics. Satellite surveillance studies have shown that secondary eyewalls are common in fully mature TCs (those that present the largest risk to our societies) and SEF has been linked to the growth of storm size and rapid intensity changes. Despite this relevance, SEF dynamics remain elusive and can present challenging forecasting applications.

There are a number of competing hypotheses aiming to capture the essential dynamics of SEF and a variety of numerical frameworks (axisymmetric, barotropic, idealized and realistic convection permitting models) have been used to support them. However, whether highly idealized numerical models are suitable to study the problem has been questioned and the convection-permitting models are often used to study just one case, preventing any assessment of the generality of the conclusions.

We present an analysis based on a variety of mesoscale integrations of the NCAR Advanced Hurricane WRF model at 1.33 km resolution. In this analysis, SEF dynamics is studied in the context of a new paradigm of TC spin up, and its azimuthally-averaged elements via the convergence of absolute angular momentum. The role of the mean dynamics and `eddy' processes in SEF will be discussed and the conclusions are supported by realistic simulations of Katrina and Rita (2005), and Igor (2010).