From a GCM simulation of a period in EASOE, the evolution of the northern hemisphere polar vortex is examined by means of a sequence of three dimensional visualization. Use is made of two key dynamical features, the edge of the polar vortex and the height of the tropopause. This technique clearly shows how the vortex is distributed by an anticyclonic tropospheric anomaly and how this disturbance vertically propagates up to the vortex. An objective method for finding the edge of the vortex is presented. ¿American Geophysical Union 1994