The method of singular spectrum analysis (SSA) is used to describe low-frequency atmospheric variability over the extratropical Northern Hemisphere (NH) from 500 hPa geopotential heights. Analysis reveals significant intraseasonal and interannual oscillations confined principally to eastern sections of the Pacific Ocean and northern sections of the Atlantic Ocean, Generally where earlier studies have identified persistent anomalies. From the results it is suggested that persistent anomalies may undergo significant modulation on the quasi-biennial time scale. ¿ American Geophysical Union 1992