Latitude-dependent characteristics of long-period geomagnetic micropulsations

In summer 1969 a line of 7 magnetic stations was set up in western Canada between the geomagnetic latitudes of 59° and 77°N and within ∼2° of 302°E corrected geomagnetic longitude. This paper concerns the analysis of the horizontal components of quasi-monochromatic, geomagnetic micropulsations recorded at these stations over 3 days. Both the amplitude spectra and the sense of polarization of the micropulsations exhibit marked latitude dependence, thus implying that much of the micropulsation energy is distributed in the toroidal mode of eigenoscillations of the geomagnetic lines of force. A switch in the sense of polarization around 1200–1400 LT strongly suggests that Pc micropulsations are generated through the development of Kelvin-Helmholtz instabilities at the magnetopause.