We report the first spatially and temporally continuous observations of the upward electric field in the E-region using the Arecibo incoherent scatter radar. This is achieved by employing the dual beam incoherent scatter radar measurements of ion velocity and using a theoretical ion-neutral collision model. The derived daytime vertical electric field, from ∼105 km to 145 km, shows large height variation, as in previous nighttime rocket measurements. Assuming that the electric field along the field line is negligible, the height variation is the same as the horizontal variation at Arecibo. Although the height variation has been attributed to gravity waves in previous studies, this explanation is not consistent with the temporal characteristics in our observation. We further discuss the error sources that affect the measurement of the electric field.