| Description |
In seemingly similar environments, some moderately sheared tropical storms undergo rapid intensification (RI) evolving towards more symmetrical precipitation structures but others do not. What distinguishes those moderately sheared tropical storms that intensify from those that do not, and how do they evolve towards symmetry? We use a 15-year passive microwave dataset to examine precipitation in a shear relative framework. Differing from previous satellite composite studies, we demonstrate that both asymmetric deep convective bursts and symmetrization of other precipitation modes play key roles in the intensification pathway. Additionally, using a 28-year ERAINTERIM dataset shear-relative environmental variables (mid-tropospheric relative humidity, RH and vertical wind shear) we differentiate RI from SI. An observational case study of Edouard (2014) links the removal of unfavorable, dry layers in the upshear quadrants to increasing precipitation symmetry. Edouard's cloud resolving ensemble shows that persistent deep convection downshear helps vortex alignment, a more favored configuration for mid-upper horizontal water vapor advection into the upshear quadrants. Evaporation from stratiform precipitation and anvil sublimation further moistens the mid-upper troposphere upshear, supporting sustained convection and precipitation symmetry. From idealized ensembles using time-varying point downscaling (TVPDS), we postulate that the humidity increases from sublimation upshear do not necessarily improve iv precipitation longevity. Rather, they reflect an increasingly favorable upper tropospheric kinematic environment for RI. Lower-middle tropospheric RH increases, on the other hand, more directly aid humidification and precipitation symmetry. |
