Lack of Vertical Co‐Location Between Aerosols and Clouds Biases the Satellite‐Based Quantification of the Twomey Effect

Abstract Uncertainties in aerosol–cloud interactions (ACI) remain significant. Recent studies report an anti‐Twomey phenomenon, where cloud droplet effective radius (R e ) exhibits a positive correlation with aerosol optical depth (AOD), contrary to the classical Twomey effect. Using long‐term satellite and reanalysis data over East Asia, we found a strong positive R e ‐AOD correlation. Further analysis reveals that AOD, as a column‐integrated quantity, lacks aerosol vertical information and cannot fully represent cloud condensation nuclei (CCN), potentially misleading the interpretation of the Twomey effect. Consequently, we analyzed aerosol vertical profiles and introduced a metric, Elevated Aerosol Ratio (EA ratio ), defined as the ratio of aerosol concentration integrals above and below clouds. Higher EA ratio values correlated with a stronger anti‐Twomey phenomenon, while lower values aligned with the classical Twomey effect. Notably, the anti‐Twomey phenomenon primarily appeared under low liquid water path (LWP) conditions: as LWP increased, both the anti‐Twomey phenomenon and the influence of EA ratio diminished. Moreover, the marine anti‐Twomey phenomenon is linked to pollution. Elevated aerosol layers in heavily polluted nearshore areas—driven by anthropogenic emissions and atmospheric dispersion—distort the R e ‐AOD relationship. Additionally, while coarse aerosols suppress marine anti‐Twomey phenomenon, the EA ratio ‐based analysis remains valid when excluding their influence as much as possible. Our findings demonstrate that the observed anti‐Twomey phenomenon is primarily a statistical artifact arising from the lack of vertical co‐location between aerosols and clouds. This mismatch biases the satellite‐based quantification of the Twomey effect when column‐integrated AOD is used as a proxy for CCN.