Validation of the Cloud_CCI (Cloud Climate Change Initiative) cloud products in the Arctic

Abstract. The role of clouds in the Arctic radiation budget is not well understood. Ground-based and airborne measurements provide valuable data to test improve our understanding. However, ground-based are intrinsically sparse, observations snapshots time space. Passive remote sensing from satellite sensors offer high spatial coverage an evolving series, having lengths potentially decades. detecting by passive challenging over because brightness snow ice ultraviolet visible spectral regions small temperature contrast surface. Consequently, quality resulting cloud products needs be assessed quantitatively. In this study, we validate retrieved Advanced Very High Resolution Radiometer (AVHRR) post meridiem (PM) polar-orbiting NOAA-19 compare them with those derived instruments during sunlit months. AVHRR European Space Agency (ESA) Cloud Climate Change Initiative (Cloud_CCI) project uses IR bands determine properties. four high-latitude sites have been selected for investigation: Hyytiälä (61.84∘ N, 24.29∘ E), North Slope Alaska (NSA; 71.32∘ 156.61∘ W), Ny-Ålesund (Ny-Å; 78.92∘ 11.93∘ Summit (72.59∘ 38.42∘ W). liquid water path (LWP) microwave radiometers, while top height (CTH) has determined integrated lidar–radar measurements. products, mask optical depth (COD), using NSA, whereas LWP CTH investigated Hyytiälä, Ny-Å, Summit. Cloud_CCI COD results better agreement NSA radiometer than clouds. For clouds, underestimated roughly 3 (OD) units. When included, underestimation increases about 5 OD overestimated ≈7 g m−2, ≈16 Ny-Å ≈24 m−2. Over Summit, CCI values ≤20 m−2 >20 Overall retrievals within instrument uncertainties. To understand effects multi-layer on retrievals, statistics compared between single-layer all types (single-layer + multi-layer). product overestimates included (i.e., types), observed overestimation becomes 360–420 m. station showed highest biases other three sites. scale-dependent differences data, Bland–Altman method applied. This does identify any parameters except station. summary, agree reasonably made at