Inferring processes governing cloud transition during mid-latitude marine cold-air outbreaks from satellite

<p>Cloud morphological transitions strongly influence radiative effects and the regional radiation budget. Marine cold-air outbreaks (MCAOs) over the northwestern Atlantic feature such transitions. Characterizing these transitions requires an understanding of the thermodynamic and dynamical evolution of the marine boundary layer and the interplay between warm- and cold-phase cloud processes. Using a novel “space-time exchange” approach, we construct instantaneous trajectories using reanalysis winds and extract geophysical variable traces along these trajectories from GOES-16 satellite snapshots for five MCAO events. Directionality of traces in liquid water path (LWP)-droplet number (<span class="inline-formula"><i>N</i>_d</span>) space reveals sequential dominance of drop activation, condensational growth, and collision-coalescence during cloud thickening. Traces in domain-mean LWP-IWP (ice water path) space exhibit two distinct couplings between liquid and ice, consistent with different mixed-phase process fingerprints: (i) gradual liquid depletion dominated by vapor deposition and (ii) rapid liquid depletion driven by collisional freezing, aided by precipitation and dynamical feedbacks. NASA-ACTIVATE in-situ measurements provide independent evidence supporting the interpretation of these process fingerprints. Delayed cloud breakup during the 29 March 2022 event is consistent with a shift from precipitation- to entrainment-driven cloud breakup under high <span class="inline-formula"><i>N</i>_d</span> conditions. During the transition to a broken cloud field, two distinct scalings between shortwave albedo and cloud fraction emerge, consistent with the identified mixed-phase process fingerprints, with the degree of cloud organization converging toward the end of the transition. These results demonstrate an effective “space-time exchange” framework for process inference from satellite snapshots, enabling a new pathway for synergistic characterization of mixed-phase microphysics in models and observations.</p>