Micropulsations in the morning sector. I. Ground observations of 10- to 45-second waves Tungsten, Northwest Territories, Canada

A study of several 10- to 45-sec wave events in the morning sector at Tungsten, Northwest Territories, Canada (approximately at the foot of the ATS 1 field line), reveals that at least two distinctly different types of wave phenomena occur. Digital power spectral and coherency analysis has been used to determine the average characteristics of the two types of waves. The first, identified as Pi 1, is characterized by a broad-band spectral enhancement with an average center frequency of ∼0.07 Hz (∼14 sec), nearly linear E-W polarization, and a close association with substorms. The second type, Pc 3, is characterized by narrow spectral lines at an average frequency of ∼0.04 Hz (∼27 sec), nearly linear N-S polarization, and no close association with substorms. Although these two types of wave activity occur in the same local time sector, sometimes simultaneously, there is no indication of any relationship between them.