A global assessment of warm-phase convective invigoration from aerosol-cloud interactions. Part 2: Observations

Abstract. The hypothesis of warm-phase convective invigoration from aerosol-cloud interactions posits that aerosol pollution increases the cloud-droplet number concentration in the liquid layer of convective clouds, causing rising air parcels to consume supersaturation more readily. This leads to smaller supersaturations, larger buoyancies, and faster updrafts. We consider this mechanism to be substantial if it increases the updraft speed w by 25 % or more when the cloud-droplet number concentration increases by a factor of five. A theoretical prerequisite for substantial invigoration is that supersaturation must exceed ~0.9 % if w = 3 m s^-1 and ~5 % if w = 7 m s^-1. This work searches for evidence of these high supersaturations in 12 globally distributed aircraft campaigns that collectively measure shallow and deep convection over ocean, coasts, and land. The quasi-steady approximation is applied to estimate supersaturation in liquid elements of convective updrafts with ~100 m horizontal resolution. Across the 13,342 total samples, 463 samples have supersaturation between 1 % and 5 %, seven samples have supersaturation between 5 % and 9 %, and no samples have supersaturation exceeding 9 %. Cloud susceptibility to warm-phase invigoration is quantified as the fraction of updrafts with supersaturation exceeding the threshold for substantial invigoration. 62 % of oceanic updrafts are susceptible when 1 ≤ w < 2 m s^-1, but only 1 % are susceptible when w > 5 m s^-1. 14 % of coastal and continental updrafts are susceptible when 1 ≤ w < 2 m s^-1, but only 0.05 % are susceptible when w > 5 m s^-1. These results imply that precipitating shallow cumuli over the ocean are uniquely susceptible to warm-phase convective invigoration.