Quasi-Steady State Supersaturation: Do High Values Derived from ESCAPE Represent Real High Supersaturations and the Potential for Condensational Invigoration?

Deep convective clouds were intensively sampled during the Experiment of Sea Breeze Convection, Aerosols, Precipitation, and Environment (ESCAPE) with coordinated flights of the NRC Convair-580 and SPEC Learjet. A total of 219 updraft core segments were sampled over coastal Texas and Louisiana under diverse meteorological conditions. Median updraft properties included widths of ~1 km, velocities of 5.5 m s-1, droplet number concentrations of ~400 cm-3, and liquid water contents of ~1 g m-3. The limitations of using the quasi-steady state approximation to derive supersaturations were explored. Supersaturation (SQSS) estimated from in situ observations under a quasi-steady state assumption averaged 0.4% but occasionally exceeded 2%, with values > 1% (high supersaturations)identified as statistical outliers. Two case studies illustrated the conditions linked to high supersaturations. In a storm over the Gulf, median core SQSS reached 2.46% in the developing stage compared to 2.17% in the mature stage under similar thermodynamic conditions. In a storm over coastal Louisiana, SQSS peaked near 11% within a 13.7 m s-1 updraft, accompanied by predominantly supercooled liquid droplets at –13 oC and exceptionally low diameter concentrations of 0.29 mm cm-3. Bootstrap analysis of all sampled cores showed that high supersaturations are most probable in cold and mixed-phase regimes with moderate to strong updrafts and are strongly influenced by vertical velocity and droplet number concentrations. While extreme supersaturations (~10%) were rare, their occurrence underscores the need for targeted multiplatform observations to resolve their spatiotemporal variability and assess their potential role in deep convective invigoration.