This collaborative project has two primary goals: (1) to resolve a long-standing discrepancy in data/model comparisons of electron energy balance in the mid-latitude F-region ionosphere from ~105-600 km, and (2) to assess potential secular temperature trends associated with global change. Both studies will utilize highly-precise measurements of ionospheric composition and temperature acquired from incoherent scatter radar (ISR) at Arecibo Observatory, Puerto Rico, under both active and quiet solar cycle conditions.