Variation in Size and Location of the 300 mb North Circumpolar Vortex Between 1963 and 1975

Abstract

Abstract The time variation in size and location of the 300 mb north circumpolar vortex has been estimated from mean monthly polar stereographic maps for the years 1963–75, both by planimetering the area north of height contours in the main belt of westerlies and by determining the colatitude of these contours at 30° longitude intervals and squaring the average value. It is shown that the vortex areas determined by the two independent techniques are in excellent agreement, but that the vortex-center locations (based on equalization of arms) determined by the two techniques are in only fair agreement. The change in vortex area appears mainly to reflect a change in mean tropospheric temperature, but with some modification caused by a change in mean surface pressure in temperate latitudes. Since 1970 the yearly averaged vortex area has increased by almost 2%, but that increase apparently ended in 1975, suggesting that the cooling in north temperate latitudes has also ended. During this same five-year period ...