Examples of storm enhanced density (SED) formation over Russia and Northern Europe are presented. These events, which persisted 15–20 hours, were fixed in local time near noon over Europe and then later observed over the American sector. The amount of total electron content (TEC) at the base of the SED erosion plume is found to be greatest in the American sector. A persistent, repeatable pattern is apparent in the time evolution of the latitude location of the SED plume base, although the latitudinal rate of change differs between the two sectors. In the European sector the invariant latitude (Λ) of the SED plume base is observed to be between 61°–63° Λ and at a time close to local noon. In the American sector, the position of the base of the plume shifts from local noon towards dusk, and moves to a lower latitude at a nearly fixed longitude.