Modeled ground magnetic signatures of flux transfer events

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.