We have carried out a comparative study of the evening prereversal enhancements in the equatorial F region vertical ionization drift velocities (Vz) over Fortaleza (4 ¿S, 38 ¿W), Brazil, and Jicamarca (12 ¿S, 77 ¿W), Peru, two magnetic equatiorial stations in the American zone. The results show profound dissimilarities in the seasonal trends in the times and widths of the Vz prereversal peak, which reflect in the spread F characteristics as well, at the two stations. The dissimilarities are shown to be arising mainly from the difference in the magnetic field declination angles that causes differences in the conjugate E region sunset durations and, hence, in the F region polarization electric field development rates at the two stations.