The magnetic field on the ground due to a small (≤200 km scale size) localized field-aligned current system interacting with the ionosphere is calculated in terms of an integral over the ionospheric distribution of field-aligned current. Two different candidate current systems for flux transfer events (FTEs) are examined. The first system has current flowing down the center of a cylindrical flux tube with a return current uniformly distributed along the outside edge. The second system has upward current on one half of the perimeter of a cylindrical flux tube with downward current on the opposite half. The peak magnetic field on the ground is found to differ by a factor of 2 between the two systems, and the magnetic perturbations are in different directions depending on the observer's position. Assuming the current system moves in a constant linear poleward direction, we predict the ground magnetic field versus time which would be measured by a ground observatory. Using FTE detection statistics at the magnetopause, we estimate the detection rate of FTEs at a ground station under the dayside convection reversal to be between 12 and 60 min per sighting depending on which FTE current system is considered. ¿ American Geophysical Union 1987