Relation of size and displacement of the 300 mbar north circumpolar vortex to QBO, El Nino, and sunspot number, 1963-2000

Abstract

The size of the 300 mbar north circumpolar vortex, and its eastern, western, date line, and Greenwich hemisphere components, is estimated for the period 1963-2000 by planimetering the area poleward of 300 mbar contours in the main belt of westerlies on the mean-monthly polar stereographic analyses of the Institute of Meteorology of the Free University of Berlin. On the basis of the superposed epoch method, there is little evidence of a relation between vortex size and phase of the QBO, but significant at the 90% level or better is the tendency for the vortex to be less displaced into the eastern hemisphere in the east-wind phase of the QBO, for the vortex to be expanded near the time of Nino 3 sea surface temperature maximum (El Nino) but contracted 3-4 seasons after, and for the vortex to be displaced farther into the date line hemisphere when there is an El Nino. There is also an impressive tendency for the winter vortex to be less displaced into the eastern hemisphere at the time of El Nino. The tendency for the vortex to be contracted near sunspot maximum, and expanded near sunspot minimum, is significant at only about the 80% level because of the small sample size.