Substorm-associated field-aligned currents have been studied using magnetic field observations at synchronous orbit and on the ground. The GOES 2 and GOES 3 satellite pair, separated in local time by about 2 hours, clearly demonstrates local time dependence of field-aligned current signatures at synchronous orbit. We have made comparisons between magnetic disturbances at synchronous orbit and ground mid-latitude magnetic disturbances. In the morning region and the evening region, D perturbations at two locations have the same sign, indicating that major field-aligned currents are those flowing into (out of) the ionosphere located on L shells greater than the spacecraft L shell in the morning (evening) region. However, the D perturbations at synchronous orbit are more transient than those on the ground in the same local time meridian. Near midnight an opposite sense for the sign of D between synchronous orbit and the ground is frequently observed. In such a case the D perturbation is always negative at synchronous orbit, while the ground D perturbation is positive. We propose that the downward current sheet extending from the morningside overlaps the upward current sheet extending from the eveningside in the center of the current system. In this model the double field-aligned current sheets are formed in association with the onset of a substorm expansion phase near the midnight meridian, and the meridian for the major field-aligned currents flowing into the ionosphere shifts progressively eastward in the morning region and the meridian for the major field-aligned currents flowing out of the ionosphere shifts progressively westward in the evening region as substorms progress. These field-aligned currents should have the longitudinally limited extent, and they most likely correspond to small-scale structure in the large-scale current system derived on the basis of low-altitude observations. ¿American Geophysical Union 1987