Modeling the magnetic effects of field‐aligned currents

In this paper, I present a newly developed model of the magnetic effects of field‐aligned currents. The magnetic field of a large‐scale field‐aligned current system is obtained by summing the magnetic fields of a large number of finite length cylindrical current elements. The resulting magnetic field is valid inside of, near and far away from the model field‐aligned currents, both near the ionosphere and in the magnetosphere. The modeling technique allows for the closure of the field‐aligned currents along any specified path. In order to investigate the effects of field‐aligned currents on the nightside magnetospheric magnetic field and on mapping between the night‐side magnetosphere and ionosphere, I add the effects of region I and II field‐aligned currents to an empirical magnetic field model. Using this model, I demonstrate the following three things: (1) reasonable amounts of field‐aligned current can cause the ionospheric footprint of a point at geosynchronous orbit to shift in local time by one hour or more; (2) depending on how they are closed, field‐aligned currents can cause B z in the equatorial plane, near midnight, either to increase or to decrease; (3) CPS field lines can cross the equatorial plane 10 R E or more further from the noon‐midnight meridian than they would if field‐aligned current effects were not included, a result that also depends on how the currents are closed.