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.