The magnetic field often exhibits a maximum in the Earth's low-latitude boundary layer. We show examples of this behavior, using data from the AMPTE/IRM spacecraft, and argue that two fundamentally distinct causes exist for the excess field: (i) a depression, within the layer, of the population of medium-energy ions of magnetospheric origin; (ii) field curvature effects associated with undulations of the magnetopause itself. ¿ American Geophysical Union 1992