Association between Geotail plasma flows and auroral poleward boundary intensifications observed by CANOPUS photometers

Poleward boundary intensifications are nightside geomagnetic disturbances t hat have an auroral signature that moves equatorward from the poleward boun dary of the auroral zone. They occur repetitively, so that many individual disturbances can occur during time intervals of similar to 1 hour, and they appear to be the most intense auroral disturbance at times other than the expansion phase of substorms. We have used data from three nightside conjun ctions of the Geotail spacecraft in the magnetotail with the Canadian Auror al Network for the OPEN Program Unified Study (CANOPUS) ground-based array in central Canada to investigate the relation between the poleward boundary intensifications and bursty plasma sheet flows and to characterize the bur sty flows associated with the disturbances. We have found a distinct differ ence in plasma sheet dynamics between periods with, and periods without, po leward boundary intensifications. During periods with identifiable poleward boundary intensifications, the plasma sheet has considerable structure and bursty flow activity. During periods without such poleward boundary intens ifications, the plasma sheet was found to be far more stable with fewer and weaker bursty flows. This is consistent with the intensifications being th e result of the mapping to the ionosphere of the electric fields that give rise to bursty flows within the plasma sheet. Two different types of plasma sheet disturbance have been found to be associated with the poleward bound ary intensifications. The first consists of plasma sheet flows that appear to be the result of Speiser motion of particles in a localized region of th in current sheet. The second, seen primarily in our nearest-to-the-Earth ex ample, consists of energy-dispersed ion structures that culminate in bursts of low-energy ions and isotropic low-energy electrons and are associated w ith minima in magnetic field and temperature and maxima in ion density and pressure. Both types of plasma sheet disturbance are associated with locali zed regions of enhanced dawn-to-dusk electric fields and appear to be assoc iated with localized enhanced reconnection. Our analysis has shown that pol eward boundary intensifications are an important aspect of geomagnetic acti vity that is distinct from substorms. In addition to their very distinct au roral signature, we have found them to be associated with a prolonged serie s of ground magnetic Pi 2 pulsations and ground X component perturbations, which peak at latitudes near the ionospheric mapping of the magnetic separa trix, and with a series of magnetic B-z oscillations near synchronous orbit . Like substorms, the tail dynamics associated with the poleward boundary i ntensifications can apparently extend throughout the entire radial extent o f the plasma sheet. Color versions of figures are available at http://www.a tmos.ucla.edu/similar to larry/geotail.html.