Variability of Multilayer Cloud Field Structure over Western and Eastern Siberia in Summer and Winter in 2006–2023 Based on CALIPSO Data

One of the indicators of ongoing climate change is the evolution of cloud regimes, both in individual regions and globally. Within this framework, the long-term variability of the structure of multilayered clouds with an optical thickness of less than 15 over Western and Eastern Siberia during the summer and winter seasons from 2006 to 2023 in daytime conditions is estimated based on CALIOP lidar data (CALIPSO satellite). Multilayering refers to the presence of clouds at several levels at the same time located under each other with gaps between them. The applied methodology is based on the use of cloud classification results from daily CALIOP lidar measurements, calculation of seasonal recurrence values for each combination of cloud types in the multilayer structure, deriving time series, determining trends, and evaluating their parameters. It has been found that the fraction of clouds with different numbers of layers over both regions did not significantly change during the period under study. In Western Siberia, the fraction of two-layer clouds is 68% in summer and 71% in winter; in Eastern Siberia, 71 and 75%, respectively. The fraction of three-layer clouds in Western Siberia attains 27% in summer and 25% in winter; in Eastern Siberia, 26 and 23%. The fractions of four- and five-layer clouds do not exceed 5% in both regions together and are almost the same in the two seasons. The most frequent combinations of cloud types in multilayer clouds over Western and Eastern Siberia have been determined. Estimates of linear trends in the fraction of the most frequent combinations in multilayer clouds over the period under study are presented. The results can contribute to improving the accuracy of climate models and radiative transfer estimates.