The Anatomy of a Convective Envelope in Sheared, Rapidly Intensifying Tropical Cyclones

A new structure in some rapidly intensifying sheared tropical cyclones (TCs), deemed a "convective envelope," is identified both in satellite observations and in idealized modeling simulations. This envelope is characterized by azimuthally-localized, enhanced convection which appears with a periodicity of between four and eight hours. It is associated with a precession of the mid-level center. Each envelope contains a series of individual towers which move more quickly than the envelope itself. Due to the cold anomaly associated with the tilt of the vortex, these towers are thermally buoyant throughout the depth of the TC. These towers exhibit a unique vertical structure: they tilt outwards (from the vortex center) with height up to approximately 4 km then shift to become vertically aligned from approximately 5 km to 13 km (the top of the storm). This shift in the vertical orientation leads to the development of roll vortices. A tilt-relative analysis of the maximum mean tangential wind shows a discontinuity of the RMW at approximately 5 km height, implying the presence of a mid-level vortex before the TC undergoes rapid intensification.