Data obtained on consecutive orbits of the topside sounder Alouette enable contour maps of ƒχF2, in which local time is independent of longitude, to be constructed over North America and the North Atlantic Ocean. They (along with data from individual orbits) reveal that at night pronounced minimums of ƒχF2 exist which are narrow in latitude and extend in a magnetic east-west direction. On these maps, the minimums of ƒχF2 surround some point on the earth's surface in the region of the magnetic pole. The average position of the most southerly minimum in the vicinity of 75°W geographic longitude moves southward from about 62°N geographic latitude at 14 hours local time to a minimum latitude of about 45°N at local midnight and then northward to about 49°N at 07 hours local time. The location of this minimum varies with magnetic activity, and during magnetic disturbances it can occur 10 degrees or more south of its undisturbed location.