Characteristics of broadband ULF magnetic pulsations at conjugate cusp latitude stations

Although cusp latitude pulsation studies have for the most part focused on narrowband waves, analysis of magnetometer data from the Arctic has shown t hat the most common type of dayside long-period ULF wave activity at very h igh latitudes is broadband noise (Pi1-2), and that its occurrence and inten sity is largely controlled by solar wind velocity [Engebretson et al., 1995 ]. However, the origin of temporal variations in the intensity of these wav es is not understood. In order to further investigate these broadband waves and their origins, we present a similar data set from another season, data from a roughly conjugate site, and multi-instrument data. Comparison of co njugate station data revealed that there was a substantial fraction of days during which there was significant temporal disagreement between hemispher es, but the solar wind;velocity still appears to control overall daily inte nsity in broadband power. The coincidence of increased riometer absorption from conjugate locations with strong broadband ULF wave power suggests that precipitating energetic particles are responsible for much of the broadban d ULF noise, and further suggests that high solar wind velocity plays a rol e in precipitation of significant fluxes of energetic particles. Quantitati ve estimates based on riometer and photometer observations also indicate th at modulated electron precipitation is sufficient to drive the broadband pu lsations. We review possible source mechanisms for these broadband waves an d the precipitating electrons associated with them. Finally, the clear temp oral association between these waves and Pc5 waves on closed field lines ma y suggest a causal connection via modulations of a three-dimensional curren t system.