Assessing the comparative effects of storm-relative helicity components within right-moving supercell environments

Supercell thunderstorms develop low-level rotation via tilting of environmental horizontal vorticity (ωh) by the updraft. This rotation induces dynamic lifting that can stretch near-surface vertical vorticity into a tornado. Low-level updraft rotation is generally thought to scale with 0–500 m storm-relative helicity (SRH): the combination of storm-relative flow, |SRF|, |ωh|, and cosφ (where φ is the angle between SRF and ωh). It is unclear how much influence each component of SRH has in intensifying the low-level mesocyclone. This study surveys these three components using self-organizing maps (SOMs) to distill 15,906 proximity soundings for observed right-moving supercells. Statistical analyses reveal the component most highly correlated to SRH and to streamwise vorticity (ωs) in the observed profiles is |ωh|. Furthermore, |ωh| and SRF are themselves highly correlated due to their shared dependence on the hodograph length. The representative profiles produced by the SOMs were combined with a common thermodynamic profile to initialize quasi-realistic supercells in a cloud model. The simulations reveal that, across a range of real-world profiles, intense low-level mesocyclones are most closely linked to ωh and SRF, while the angle between them appears to be mostly inconsequential.