Pathway-dependent thermodynamic adjustment shapes cold-advection low-cloud regimes over the Eastern North Atlantic

Abstract

Marine low clouds strongly affect Earth’s radiation budget, yet climate models continue to underestimate shallow cumulus and misrepresent low-cloud regimes in cold-advection environments. Here, we combine five years of radar observations from the Atmospheric Radiation Measurement Eastern North Atlantic site with 36 h backward trajectories to examine how upstream air-mass pathways shape stratocumulus-related cloud states and vigorous shallow cumulus. Our results show that cold-advection strength alone cannot fully explain the cloud state observed at trajectory arrival; pathway-dependent thermodynamic and dynamical adjustment along the air-mass pathway must also be considered. The Sc-related states exhibit near-surface warming that outpaces moistening, whereas vigorous shallow Cu maintains a more coordinated near-surface warming and moistening pathway. This coordinated adjustment favors a relatively lower lifting condensation level and, together with stronger surface buoyancy flux, provides a favorable environment for active shallow convection. These findings highlight the importance of pathway-dependent warming–moistening adjustment for understanding differences in low-cloud development under cold-advection conditions. They also provide an observational reference for the near-surface thermodynamic conditions and surface forcing accompanying low-cloud evolution in climate-model simulations under cold-advection conditions.