Bidecadal and Pentadecadal Climatic Oscillations over the North Pacific and North America

Climatic variations on bidecadal (about 20 years) and pentadecadal (50–70 years) timescales are analyzed in terms of their seasonal and regional dependencies in the North Pacific and North American sector. The both bidecadal and pentadecadal variations are evident in SLP fields associated with the strength changes of the Aleutian low. The bidecadal variability is evident only in winter both in the SLP and air-temperature fields, whereas the pentadecadal signal exists from winter to spring seasons in the SLP field and only in spring in the air-temperature field. The SLP structure of the pentadecadal variability is approximately unchanged through the present century. The bidecadal variability exhibits frequency decrease (period increase) from 1930 to 1950, and simultaneously the center of the variability migrated southward. The century scale modulation of the bidecadal signal is also supported by the fact that an out-of-phase relationship between the Aleutian low strength and air-temperature holds throughout the present century for the Alaska but only after the 1930s for the West Coast of midlatitude North America.