Latitude effects on the amplitude of Pi 2 micropulsations

The effect of latitude on the amplitude of Pi 2 micropulsations has been studied using data from Hobart, Brisbane and Lae. Theories of the source mechanism of this class of pulsation are considered and it is shown that the present results favour cavity excitation as the mode of generation. The ratio of E-W to N-S signal components is found to be appreciable at all sites and greater than unity at the high latitude station. It is also shown that Pi 2 amplitude is strongly correlated with the magnetic activity indices for the station at the higher latitude, but not for those at the lower latitudes