Interdecadal Changes of Scandinavian Teleconnection Pattern in the Late 1970s

Based on the reanalysis dataset from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) and the Precipitation Reconstruction over Land (PREC-L) dataset, this study investigates the interdecadal changes of the Scandinavian (SCAND) teleconnection pattern in boreal winter. The SCAND pattern is obtained by applying the rotated empirical orthogonal function (REOF) method on the winter mean 500-hPa geopotential height anomalies for the period from 1948/1949 to 2008/2009. The SCAND pattern consists of three primary centers of actions. One is located around the Scandinavian Peninsula and the other two have opposite signs and are located over Western Europe and Siberia, respectively. Analysis of the SCAND index reveals that the SCAND pattern was in its decadal negative phase around 1960, and from the late 1970s to the early 2000s. Its decadal positive phase occurred in the 1950s, from the early 1960s to the late 1970s, and again in recent years. A Lepage test indicates that the SCAND pattern experienced a clear abrupt change in 1979. Further analysis indicates that the centers of both SCAND patterns over Western Europe and Siberia extended further southeastward during the 1979/1980 to 2008/2009 period, as compared with those in the 1948/1949 to 1978/1979 period. The center over the Scandinavian Peninsula, however, showed little change. Accompanied with the changes in spatial pattern, the influences of SCAND pattern on the wintertime surface air temperature and precipitation also changed. For the period between 1979/1980 and 2008/2009, negative surface air temperature anomalies associated with the positive phase of the SCAND pattern over the northern Eurasian continent extended further southeastward, even reaching the lower reaches of the Yangtze River Valley and Japan. Meanwhile, the negative precipitation anomalies associated with the positive phase of SCAND pattern featured a zonally elongated band over the Eurasian continent centered at about 60°N, in contrast to the situation before 1979. Diagnostics using the geopotential height tendency equation suggest that the interdecadal changes in the SCAND pattern can be attributed to the changes in vorticity forcing by anomalous stationary waves, interactions between anomalous and climatological stationary waves, and high-frequency transient eddies.