Ionospheric climatology and variability studies are conducted using long-term incoherent scatter radar (ISR) observations from seven sites around the world. These studies result in an empirical model system, the ISR Ionospheric Model (ISRIM), which represents local and regional ionospheric climatology and variability of the ionosphere. This paper addresses some new climatological features revealed by the model for latitudes spanning 18–70°N over the eastern American sector. The latitudinal change of the F2-layer electron density exhibits a clear depletion near Millstone Hill latitudes when solar activity is median or low, accompanied by a Te enhancement, and electron density peaks at ～10° both to the north and south of Millstone Hill. Possible explanations are discussed. We also characterize several types of variation in plasma temperatures in this region, including ion temperature elevation for quiet conditions in the auroral zone and electron temperature increases toward higher latitudes.
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