The Interaction Between Trends and Periodical Components in Air and Soil Temperature Time-Series Over the Asian Territory of Russia

We used Singular Spectrum Analysis (SSA) to detect trend and periodic components (rhythms) in annual and seasonal time series of surface air temperature (SAT) and of soil temperature (ST) at depths of 40, 160, and 320 cm, for the northern (to the north of the 60th latitude) and southern (to the south of the 60th latitude) parts of Western Siberian Plain, western and eastern parts of Central Siberian Plateau, Transbaikalia, and the territory located to the east of Lena River. We analyzed SAT data from 1902 to 1995 and ST data from 1960 to 1990. SSA-detected trends in the annual ST time series generally track trends detected in the annual SAT time series. They show a statistically significant increase in annual ST down to 320 cm for the Central Siberian Plateau, Transbaikalia, and south of Western Siberian Plain. The least soil warming between 1960 and 1990 is observed for the territory east of the Lena River. SSA-detected rhythms in the annual SAT and ST time series are coincident for the north of West Siberia Plain (7.7 years) and the western Central Siberian Plateau and Transbaikalia (2.7 years), and they are close but not coincident for eastern Central Siberian Plateau (4.7 and 4.3 years for SAT and ST, respectively). No coincident rhythms were found for the south of West Siberia Plain and territory located to the east of Lena River.For the majority of the study regions, winter, spring, and autumn ST tracked the 2- to 3-year periodic components of the corresponding SAT time series. Although summer ST over the Central Siberian Plateau and Transbaikalia coincides with the 5- to 7-year rhythms in the corresponding SAT, rhythms reconstructed in the annual ST time series are mainly coincident with those in the winter ST time series. Only winter ST over the western Central Siberian Plateau tracked the 9.8-year rhythms in the corresponding SAT time series. Trend and periodic components in the summer ST time series manifested themselves in annual ST time series only for the West Siberian Plain. This work was support by the North Atlantic Treaty Organization under a Grant awarded in 2003 (DGE-0312143), as well as NSF grants OPP-0229766 and OPP-0352910