Measurement report: Diurnal cloud variability, vertical regimes, and radiative effects over Iran from multi-sensor observations

Abstract. Cloud cover, vertical structure, and diurnal timing jointly shape cloud radiative effects, but their observed variability has not been integrated over Iran. We combined CLAAS-3, CloudSat–CALIPSO, and CERES observations from product-specific periods between 2004 and 2025 to characterize cloud properties, vertical regimes, and top-of-atmosphere radiative effects. National mean cloud cover was highest in April (48.79 %) and lowest in September (13.30 %). Its daily maximum occurred at 16:34 local solar time, shifting to 19:35 in summer. Altostratus was the dominant classified regime across much of northern and central Iran, whereas cirrus was more common in the south and southeast; limited sampling makes some local classifications uncertain. CERES SYN1deg-MHour gave mean shortwave and longwave cloud radiative effects of −18.29 and 27.99 W m⁻², respectively. Their opposing associations with cloud cover were consistent with partial compensation and a weaker association with net radiative effect. Independently, CERES EBAF-TOA showed a decline in net cloud radiative effect of −0.95 W m⁻² decade⁻¹ during 2004–2024 (q = 0.034), while no national CLAAS-3 cloud-property trend remained significant after multiple-testing correction. These observations indicate that cloud amount alone does not describe cloud–radiation variability across Iran. Differences in sensor resolution and sampling, and the lack of coincident observations, limit the findings to climatological associations rather than causal attribution.