Strong Diurnal‐Dependent Meteorological Control on Long‐Term Variations of Cloud Droplet Number Concentration

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Abstract While long‐term cloud droplet number concentration (CDNC) changes are commonly attributed to aerosols, the role of meteorological factors remains poorly explored. Here, we perform a time‐resolved contribution analysis of long‐term CDNC variations using nearly two decades of geostationary observations over four Atlantic subtropical regions. The results show that sulfate aerosol acts as the primary contributor with an average contribution of ∼34%, however, total aerosol contributions explain <50% of the long‐term CDNC variability in most regions. Instead, subcloud layer stability (LTS sub ), which sustains higher CDNC by suppressing droplet growth and cloud‐top entrainment, emerges as the dominant meteorological factor with contributions comparable to sulfate and varying across local times (∼33% average contribution with a mean diurnal amplitude of ∼35%). Additionally, long‐term changes in LTS sub are mainly linked to the temperature near cloud base. These findings highlight the essential and strong diurnal‐dependent control of meteorological factors and the necessity of geostationary observations to better constrain aerosol‐cloud interactions.

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