The size of the 300 mbar north circumpolar vortex, and its partition into western and eastern hemispheres and quadrants 0¿--90 ¿W, 90 ¿W--180¿, 90 ¿E--180¿, and 0¿--90 ¿E, is estimated by planimetering the area poleward of contours in the main belt of westerlies on the polar stereographic mean-monthly analyses of the Institute of Meteorology of the Free University of Berlin. During 1963--1997 the trend in annual vortex size is a significant -1.4%/decade (vortex contraction), but with the trend in the western hemisphere portion of the vortex a significant -2.1%/decade compared to -0.7%/decade in the eastern hemisphere portion, signifying a movement of the vortex farther into the eastern hemisphere. Thus, while on average 52% of the vortex was in the eastern hemisphere during 1963--1997, this value increased by a significant 0.4%/decade during the period, resulting in a substantial increase in vortex eccentricity. In winter and spring the vortex has moved mainly into the Asian quadrant 90 ¿E--180¿, whereas in summer the vortex has become elliptical with less of a decrease in size of quadrants 90 ¿E--180¿ and 0¿--90 ¿W, and in autumn there has been a decrease in size of quadrant 90 ¿W--180¿ relative to the other quadrants. The standard deviation of the annual quadrant-size anomalies has decreased significantly during 1963--1997, indicating a decrease in the annual displacements of the vortex center from its mean location as the eccentricity increases and the vortex contracts. On the basis of a 41-station northern hemisphere radiosonde network, during 1963--1997 the annual 850-300 mbar temperature increased by a significant 0.12 ¿C/decade in the northern hemisphere as a whole, and by a significant 0.17 ¿C/decade in the western half and by 0.06 ¿C/decade in the eastern half of the hemisphere. The resulting association of a 1%/decade decrease in 300 mbar vortex size, with about an 0.1 ¿C/decade increase in 850-300 mbar temperature, differs by a factor of 2 from what would be expected hydrostatically, a difference that would be eliminated by an 0.4 mbar/decade increase in midlatitude surface pressure during 1963--1997.