Continuous measurements of electron temperature and electron concentration were made at Jicamarca from 0700 to 0830 LT and from 1130 to 2000 LT during the great magnetic storm of March 8, 1970, when the F2 peak rose as high as 800 km. Continuous measurements of the vertical component of E×B drift were made from 1130 to 1730 LT. A synthesis of the observed electron concentrations was made using a model that solved the time-dependent electron-ion continuity equation for O+ and the molecular ions; the latter chemistry was included to improve the solutions at lower heights. It was found, using the observed values of vertical drift, that most of the observed features of the F2-region ionosphere were synthesized by the model. An interpretation of the synthesis that emphasizes the importance of horizontal diffusion at the equator is given. Observations are presented for March 7, 8, and 9, 1970, including the Huancayo magnetograms, which display a close correlation with the drift measurements.