Multi-Timescale Features of Surface Air Temperature in the Source Region of the Yellow River during 1953–2017

On the basis of the annual averaged surface air temperature data from eight meteorological stations in the source region of the Yellow River obtained using the ensemble empirical mode decomposition (EEMD) approach, the multi-timescale temperature features of meteorological stations, with Madoi as a representative, during 1953–2017 and their contributions to the temperature variations are revealed. The correlations between different timescale temperature oscillations and sea surface temperature (SST) indices, particularly the Atlantic Multidecadal Oscillation (AMO), are analyzed. The results indicated that: (1) The long-term temperature trend during 1953–2017 in the source region of the Yellow River was 0.31 ℃/10 years; the warming period started in the late 1980s and accelerated in the late 1990s. (2) There were 3-, 6-, 11-, 25-, 64-, and 65-year quasi-cycle oscillations for temperature during 1953–2017. Among them, the 3- and 65-year quasi-cycle oscillations were significant. The amplitude of the 3-year timescale oscillation increased before the 21st century and decreased after the 21st century. By contrast, the amplitude of the 65-year timescale oscillation increased after the 21st century. (3) The three-year quasi-cycle oscillation was dominant during 1953–1997. Moreover, the contribution of the 65-year oscillation increased nearly five times, which was equivalent to the contribution of the 3-year oscillation during the rapid warming period since 1998. (4) The correlations of temperature with the Nino3.4 and Pacific Decadal Oscillation (PDO) indices were not significant. However, the maximum significant correlation was observed during the 22-year temperature-led PDO. In contrast to PDO, the maximum significant correlation was observed when the AMO led the original temperature and its three interdecadal components 0 and 3–7 years that supported the finding that the AMO had a significant effect on the temperature variation in the source region of the Yellow River. (5) The positive warm phase of the AMO corresponded to the warming period of East Asia, including China, and the source region of the Yellow River was only a part of that area. The negative cold phase of the AMO from the early 1960s to the early 1990s and the positive warm phase of the AMO from the middle and late 1990s to the present corresponded to the negative and positive phases of the temperature in the source region of the Yellow River. The AMO highly correlated with the 65-year oscillation. These results supported the finding that the AMO was an important climatic oscillation that affects the temperature variation, particularly the interdecadal timescales, in the source region of the Yellow River.