Banded ion morphology

Bands of ions have been observed at constant pitch angle by the Dynamics Explorer High- and Low-Altitude Plasma Instruments at auroral latitudes. The observed ion-dispersion pattern shows lower-energy ions toward the equatorward side of the band and higher-energy ions toward the poleward side of the band. Ion bands have their highest-energy flux at small pitch angles. The observed bands have been correlated with storm phase (by Dst) and substorm phase (by AE). Bands are more likely to occur during main-storm phase than during recovery storm phase. Substorm correlations are statistically significant, but there is a hint that most bands occur during substorm recovery phase. Two models have the potential of producing ion signatures that are similar to the band feature. They are the time-of-flight mechanism and the convective dispersion mechanism. Under a time-of-flight mechanism, ions are dispersed along a magnetic filed line with higher-energy particles outrunning lower energy particles. Ions are dispersed perpendicular to the magnetic field under convective dispersion. A time-of-flight effect does not explain the band energy-latitude dependence observed in the southern night or northern day very well, whereas the convective dispersion mechanism easily accomplishes this