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

Steady increase in anthropogenic emissions necessitates the investigation of their impacts on the microphysics of the deep convective clouds, particularly through the aerosol induced condensational invigoration mechanism. This hypothesized mechanism requires the presence of large supersaturations to allow for the nucleation of additional aerosols into cloud condensation nuclei (CCN) at much higher levels above the cloud base than is typical. Due to current technological limitations, supersaturations cannot be measured directly and are derived from microphysical observations assuming quasi-steady state conditions in the updraft. This study use in-situ airborne observations collected during the Experiment of Sea breeze Convection, Aerosols, Precipitation and Environment (ESCAPE) field campaign to determine how updraft core characteristics including calculated in-cloud quasi-steady state supersaturations vary with altitude, how cloud microphysical properties change in various aerosol and meteorological conditions, and thus whether there is observational evidence supportive of the potential for condensational invigoration occurring.

The National Research Council of Canada Convair-580 and Stratton Park Engineering Company’s Learjet aircraft together sampled about 300 intense convective cloud core segments in different meteorological regimes along the coast of Texas and Louisiana between 31 May and 17 June 2022. The statistics of altitude-sorted updraft core segments show larger derived quasi-steady state supersaturations (SQSS) and stronger updrafts with increased height above the cloud base. The mean SQSS was approximately 0.4%, but a case of an isolated thunderstorm ingesting clean maritime air showed a peak SQSS of nearly 10% collocated with extreme updrafts reaching up to 21 m s-1 in the mixed-phase region of the storm. This indicates the potential for condensational invigoration. Examination of other cases did find the occasional occurrence of SQSS larger than 5%, but these conditions were quite rare. Based on the observations which include airborne X-band radar, conditions where large SQSS might be expected are inferred.

Additionally, the airborne in-situ observations below cloud are used to classify convective cores into three aerosol regimes: pristine, intermediate, and polluted. After meteorologically constraining these regimes using CAPE, a higher probability of stronger updrafts in intermediate and polluted conditions, and higher probability of larger than mean SQSS in clean and intermediate conditions is found. Although these preliminary results are consistent with the condensational invigoration hypothesis, they are subject to the quasi-steady state assumption. The caveats of using SQSS and results after constraining other key meteorological variables identified using a machine learning algorithm will be presented.