Influences of atmospheric and oceanic low‑frequency climate fluctuations on European winter surface air temperatures (1870-2010)

Abstract

We isolated natural atmospheric and oceanic low-frequency climate fluctuations and its linkages with European winter surface air temperature (SAT) anomalies since 1870. Singular spectrum analysis was applied to SAT, North Atlantic sea surface temperature (SST), and the North Atlantic Oscillation (NAO) time series. The evolution of their low-frequency components was then compared with other time-series variability such as the Arctic Oscillation. The North Atlantic SST was found to be out of phase with the Atlantic sea level pressure and European SAT, following a ~65 yr climate fluctuation reminiscent of the Atlantic multi-decadal oscillation. Atlantic positive/negative SST anomalies preceded negative/positive European SAT anomalies by ~6 yr. Moreover, milder European winters occurred when a negative Atlantic multi-decadal phase overlapped a positive Arctic Oscillation phase (i.e. 1905�1915 and 1985�2000). The quasi- decadal oscillation of SST and the NAO were in-phase and led positive/negative European SAT anomalies by approximately 1 yr. The low-frequency winter SAT variability represented 22.3% of the total variance. From the mid-1980s onward, when a rapid change in climate occurred, involv- ing milder European winters, results showed that the NAO and the Arctic Oscillation phases both remained mostly positive. A strong polar vortex dominated during this period, minimizing merid- ional air-mass exchanges during winter. The anthropogenic component of climate change could modify the Atlantic thermohaline circulation, and with it the low-frequency variability of the North Atlantic SST, as well as the Arctic Oscillation variability, due to changes in the stratospheric thermal state, as shown elsewhere. These complex interactions between the Atlantic Ocean and the overlying atmosphere could have global socio-economical impacts in Europe during the 21st century.