Evolution of convective characteristics during tropical cyclogenesis

Abstract

Four idealized, high-resolution (500 m horizontal grid spacing), numerical simulations are used to investigate the evolution of convective structures during tropical cyclogenesis. The simulations all begin with a weak initial axisymmetric cloud-free vortex in a quiescent environment, but differ in the moisture level of the initial sounding and whether or not ice microphysical processes are considered. Irrespective of experimental setup, there is only a short period where shallow or congestus clouds dominate. The shallow cloud phase is slightly extended with the drier initial environmental sounding. The composite structure of the convective elements sampled changes markedly throughout the genesis period. For much of the genesis phase, vertical profiles of the mean convective cell show significant amounts of anticyclonic vorticity produced in cells in the inner core. Towards the end of the genesis phase, there is a large increase in the production of cyclonic vertical vorticity in inner-core convection, and cyclonic vorticity becomes dominant at low-mid levels. The evolution from roughly equal strength vertical profiles of cyclonic/anticyclonic vorticity at low-mid levels to profiles where cyclonic vorticity dominates occurs at relatively low system wind speeds (V max less than 10 m⋅s −1 ). This finding indicates a change in the structure of vortical convection prior to rapid intensification. In outer-core convection, there are roughly equal strength vertical vorticity dipoles produced throughout the genesis period.

Statistics of the Subgrid Cloud of an Idealized Tropical Cyclone at Convection‐Permitting Resolution

“…Although the absolute mass flux of shallow convective clouds with maximum MFH below 2 km is small (See Figure S1), they occur most frequently over the domain. Some studies showed that the shallow cumulus convection plays an important role in TC formation (Wang, 2014) and intensification (Kilroy, 2021). Due to the high frequency of occurrence, the parameterization for shallow convective clouds should be paid more attentions.…”

A Global Survey of Rotating Convective Updrafts in the GFDL X‐SHiELD 2021 Global Storm Resolving Model

“…Rotation of sub‐severe storms—those not meeting National Weather Service severe weather criteria—has apparently not been studied at all. VHTs are beginning to be observed through geostationary satellites and in some aircraft observations (Hogsett & Stewart, 2014) but most effort at understanding these uses regional simulations, and exclusively in the context of mature and intensifying tropical cyclones where there has been some effort to better understand their role in genesis and intensification (Kilroy, 2021, and references therein; Wang, 2018; Zawislak, 2020, and references therein; Hendricks et al., 2004). An appreciation for rotating updrafts elsewhere is virtually absent.…”