The Expanded North Circumpolar Vortex of 1976 and Winter of 1976–77, and Attendant Vortex Displacement

Abstract

Abstract Planimetering of the area poleward of contours in the main belt of westerlies on 300 mb mean-monthly polar stereographic maps indicates that the size of the 300 mb north circumpolar vortex was larger in 1976 than in any year since initiation of the record in 1963, and that the size of the winter vortex of 1976–77 was also the largest of record. Other “firsts” for the winter of 1976–77 include the displacement of the vortex furthest in the direction of the Greenwich meridian and the closest approach of the vortex center to the North Pole (smallest eccentricity). It is shown that the large vortex size and small eccentricity in the winter of 1976–77 are qualitatively, but not quantitatively, in agreement with the previously noted relations of these parameters with the quasi-biennial wind oscillation of the low tropical stratosphere.