Understanding the Impact of Arctic Cloud Fraction on Surface Shortwave Radiation: Recent Progress

The Arctic region is experiencing the most rapid warming on earth, significantly perturbing its surface ecosystems and energy balance. Accurately quantifying the Arctic surface radiation budget, particularly the shortwave component, is critical for understanding both regional climate change and the global energy budget. Despite ongoing advances in observational technologies and analytical methods, uncertainty in cloud fraction (CF) exerts a dominant control on the accuracy of surface shortwave radiation (SW) estimation. Existing studies indicate that Arctic clouds are dominated by low-level ice-phase and mixed-phase clouds. Daytime cloud fraction peaks in September and reaches a minimum in April, and is generally higher over ocean than over land. Most datasets suggest an overall increase in total Arctic cloudiness. However, substantial disagreements persist regarding trend magnitude, seasonal dependence, and contributions from different vertical layers, leading to SW differences of approximately 20–70 W m⁻². These discrepancies primarily arise from inconsistent CF definitions and spatiotemporal scales, sensors and sampling geometry differences, cross-calibration and processing biases, cloud detection and phase- discrimination errors over bright surfaces and during polar night, and valuation uncertainty arising from sparse and non-uniform ground-based references. Consequently, existing Arctic SW products still fall short of the requirements for energy-budget closure and climatological applications. This study synthesizes recent advances in understanding Arctic cloud fraction and its critical impact on surface SW, highlights the principal challenges, and outlines promising future research avenues. This endeavor aims to furnish a clearer scientific foundation for improving predictions of polar and global radiative energy dynamics and climate change.