The Inner-Core Temperature Structure of Hurricane Edouard (2014): Observations and Ensemble Variability

The inner-core thermodynamic structure of Hurricane Edouard (2014) is explored, primarily through the utilization of high-altitude dropsondes deployed during NASA’s Hurricane and Severe Storm Sentinel (HS3) campaign, and a 60-member convection-permitting ensemble initialized with an ensemble Kalman filter. The 7-day forecasts are initialized coincident with Edouard’s designation as a tropical depression and include Edouard’s significant intensification to a major hurricane. Ten-member ensemble groups are created based on their timing of near rapid intensification (RI) onset, and the associated composite inner-core temperature structures are analyzed.

Inner-core perturbation temperatures calculated using an environmental reference profile reveal that at Edouard’s peak intensity, in both the observations and the simulations, the maximum perturbation temperature (~10–12 K) occurs in the mid levels (~4–8 km). In addition, in all composite groups that significantly intensify, the evolution of the area-averaged inner-core perturbation temperatures indicate that weak to moderate warming (at most 4 K) begins to occur in the low- to mid levels (~2–6 km) ~24–48 h prior to RI, and this warming significantly strengthens and deepens (up to ~8 km) ~24 h after RI has begun. Despite broad similarities in the evolution of Edouard’s warm core in these composites, variability in the height and strength of the maximum perturbation temperature and in the overall development of the inner-core temperature structure are present amongst the members of the composite groups (despite similar intensity time series). This result suggests, and is supported by correlation analyses, that little to no relationship exists between the strength or height of the maximum perturbation temperature and RI onset in this ensemble when current intensity is controlled for, and fluctuations in inner-core temperature structure occur either in tandem with or after significant intensity changes.