A Coherence-Limited Dynamical Selector for Convective Organization

Classical convective indices such as Convective Available Potential Energy (CAPE) and storm-relative helicity (SRH) quantify thermodynamic energy and rotational potential but often fail to explain why similar environments produce either long-lived organized convective systems or short-lived pulse storms. This work introduces a minimal, falsifiable dynamical index—the RMB index—that quantifies the structural coherence of atmospheric motion over its self-organization timescale. The index is explicitly orthogonal to thermodynamic forcing and rotational measures and is designed to act as a selector for convective organization states rather than intensity. Using reconstructed proximity soundings from two well-documented Alpine cases (the 18 July 2005 Lake Geneva tornadic supercell and the 7 August 2015 Alpine foreland pulse-storm environment), the RMB index cleanly separates environments with similar CAPE and SRH but different convective outcomes. The resulting CAPE–RMB phase space provides a physically motivated classification of convective organization without claiming improved intensity, tornado, or operational forecasting skill. Exact ERA5-based reproduction is straightforward and planned as future work.