Edouard's (2014) Intensification: The Relationship between Precipitation Symmetry, Quadrant-Based Thermodynamics, and Vortex Tilt using a Cloud-Resolving Ensemble

Recent satellite-based composite studies have emphasized the importance of “moderate” precipitation symmetrization prior to the onset of rapid intensification (Zagrodnik and Jiang 2014, Tao and Jiang 2015, Alvey et al. 2015). One potentially important process, the humidification of upshear quadrants in the middle troposphere, has been identified to occur nearly coincidental with increased precipitation symmetry prior to and during Edouard’s (2014) intensification (Zawislak et al. 2016). Modeling studies (Rios-Berrios et al. 2016, Munsell et al. 2017) analyzing moderately sheared TCs have also shown the importance of vortex alignment and mid-level moistening for TC intensification. Fundamental questions, however, remain unanswered regarding the precipitation symmetrization prior to rapid intensification onset: What causes precipitation to symmetrize before rapid intensification onset, how does the vortex become vertically aligned, and what’s the relationship with precipitation symmetry?

While observations from the Global Hawk and P-3 provided important snapshots throughout the life cycle of Edouard (Zawislak et al. 2016), numerical models complement and reveal, in more detail, the processes behind these relationships through filling an ~48 hour airborne observational gap during a crucial period of intensification between 12–14 Sept. We use a high resolution, full physics ensemble of Edouard (2014) simulated by the Weather Research and Forecasting (WRF) model – Advanced Research WRF (ARW; Skamarock et al., 2008). We deem the quantification of azimuthal variations — with a focus on the shear-relative quadrants — as particularly important, especially early in intensification when wind and precipitation distributions tend to be more asymmetric. We examine whether precipitation is responsible for upshear humidification (moistening), or if an increase is due to advection from the environment, or simply a result of vortex alignment (perhaps due to a decrease in vertical shear). We present detailed temperature and water vapor mixing ratio budgets within a quadrant based framework to demonstrate the processes governing the transition from an asymmetric to more symmetric tropical cyclone.