The magnetic local time distribution of long-period absorption pulsations has been determined for sites from L=4 to L=13.5. In addition, satellite crossings of unstable boundary regions of the magnetosphere have been used to study the correlation between the Kelvin-Helmhlotz instability and pulsating ionospheric absorption. The results of this study show that almost half of the instances of boundary instability are accompanied by simultaneous absorption pulsations.