Abstract: This paper investigates the climatic state and seasonal variation characteristics of the three-dimensional structure of Arctic cloud fraction based on the three-dimensional spatial data of CALIPSO clouds averaged over the multi-year climate months from 2007 to 2020. The results show that the Arctic cloud fraction is mainly distributed in the atmospheric boundary layer and troposphere, and the cloud fraction decreases from the boundary layer to the upper layer; the horizontal spatial distribution mainly shows significant sea-land differences, and the maximum cloud fraction occurs in the Arctic Atlantic sector; the vertical structure shows a positive pressure structure with the in-phase change above and below the troposphere and a first-order oblique pressure mode structure with inverse phase change between the lower atmospheric boundary layer and the middle and upper troposphere. The cloud fraction over the ocean is larger than that over the Arctic land, while the opposite is true in the upper and middle troposphere. The Arctic cloud amount mainly shows the seasonal variation of single-peak type, with the least amount of cloud fraction in February and March and the most amount of cloud fraction in September. The seasonal variation of Arctic clouds is mainly reflected in the two main spatial and temporal modes of cloud fraction in the boundary layer of the low atmosphere, the first mode mainly reflects the inverse phase variation of Arctic melt (May–October) and freezing (November–April), with a variance contribution of 59.35%. The second mode mainly reflects the inverse phase variation of land-sea differences in the Arctic in late autumn (October–November) and early summer (June–July), with a variance contribution of 19.22%.

Key words: Arctic, cloud fraction, vertical structure, seasonal variability, sea-land differences