An isolated substorm occurred on October 21, 1981 at the end of a large geomagnetic storm. Observations of particles and fields were made during the presumed growth phase of this substorm by the DE 2 satellite. The ionospheric convection at the time indicates a pattern commonly observed during the maximum of substorms with convection velocities averaging ~500 m/s in an eastward channel of flow in the premidnight sector. Despite the convection signature, geomagnetic conditions were quiet with the AL index >-50 nT and very weak field-aligned current. We will present an in-depth study of the nightside gap region within the channel of eastward flow. We will discuss the possible effects of a neutral wind flywheel on the convection. Also, we will present a detailed analysis of the electrodynamic structures within the nightside gap which indicates a magnetospheric source. Possible ionospheric signatures of the tail neutral line are discussed. ¿ American Geophysical Union 1996