A robust stepwise jump in the Arctic wintertime warming in 2005 coherent with the increased clear-sky downward longwave radiation flux

In some areas of the Arctic, the Earth's surface temperature and near-surface air temperature are rising faster than in others. The purpose of this study is to identify, based on the ERA5 climate reanalysis data, the spatiotemporal structure of climatic changes in the Arctic during 1959-2022. The main emphasis is put on the following three parameters: mean surface clear-sky downward longwave radiation flux, near-surface air temperature, and skin temperature. A statistical model of stepwise changes was applied to the time series of the studied characteristics at each grid point of the entire Arctic (67 degrees N-90 degrees N). The results obtained indicate a close relationship between all parameters in the winter season. The dominant year of stepwise changes in the Arctic is 2005. Moreover, it is precisely this transition from one state of the climate system to another that is statistically significant over a large territory, which is located mainly in the Eastern Hemisphere. The time series averaged over the identified areas are highly correlated with each other, and the year 2005 characterizes the change from a sharp increase in values to their variability without a pronounced trend. The available satellite observations fully confirm the temporal structure of the stepwise changes for the studied parameters and largely confirm its spatial structure. Thus, the clear-sky downward longwave radiation flux is one of the leading factors in the formation of the thermal regime of the Arctic.