A network of stations near the 70¿W meridian has been used to monitor continuously the polarization of the VHF beacon signal from the geostationary satellite ATS 3. Measurements of the amount of Faraday rotation experienced by the signal in traversing the ionosphere permit continuous observations of the ionospheric total electron content (TEC) to be made over the invariant latitude range 34¿--73¿. When the TEC data are combined with ground-based ionosonde data from nearby locations, it is also possible to monitor the peak density (Nmax) of the F2 region and the equivalent slab thickness (&tgr;=TEC/Nmax). Observations from six stations made in December 1971 were used to construct computer-generated contour maps of the TEC,Nmax, and &tgr; monthly median behavior on an invariant latitude (&Lgr;) versus local time grid. Comparisons between daily TEC contours and the monthly median contours reveal dramatic effects induced by substorms (December 8--9) and major geomagnetic activity (December 17--18).