Relation between 300-mb North Polar Vortex and Equatorial SST, QBO, and Sunspot Number and the Record Contraction of the Vortex in 1988–89

Abstract

The size of the 300-mb north circumpolar vortex and quadrants has been estimated between 1963 and 1989 by planimetering the area poleward of contours in the main belt of westerlies on the 300-mb mean-monthly polar-stereographic maps analyzed by the Meteorological Institute, Free University of Berlin. The annual-mean vortex was most contracted in 1989, 6.4% less than average size, and next most contracted in 1988, 4.6% less than average size. There have been three extensive vortex displacements during this period, the last toward the North Pacific and associated with the strong El Niño of 1982?83. Based on 108 seasonal deviations, there has been a significant correlation of ?0.39 between sea surface temperature (SST) in the eastern equatorial Pacific and vortex size three seasons later, that is, the vortex has tended to be contracted following El Niño. There has been a highly significant correlation of 0.45 between this SST and the size of quadrant 90°W-180° in the same season, that is, this ?El Niño? quadrant has tended to be expanded at the time of El Niño. The correlation of ?0.29 between the 50-mb zonal wind at Singapore and vortex size one season later (contracted vortex in the west-wind phase of the stratospheric equatorial QBO) is not significant. There is better evidence for contraction of the vortex in the west-wind phase of the QBO when the sunspot number is relatively high.