Abstract
Equatorial noise (EN) emissions are electromagnetic waves observed routinely in the equatorial region of the inner magnetosphere. Although they are typically continuous in time, they sometimes exhibit a quasiperiodic (QP) time modulation of the wave intensity, with modulation periods on the order of minutes.
We perform a detailed analysis of 118 EN events with the QP modulation. The events are observed preferentially outside the plasmasphere.
We determine the times and frequencies of individual QP elements forming the events. Apart from the event modulation period, this allows us to characterize the intensity and the frequency drift of individual QP wave elements.
It is shown that the element intensity peaks at the magnetic equator. The modulation period within a single event is usually quite stable, with variations lower than 25% of the median value in the vast majority of cases.
The events with shorter modulation periods are typically more intense, and they tend to have larger frequency drifts. These relations resemble the relations formerly revealed for extra low frequency/very low frequency quasiperiodic emissions, suggesting that the origin of the QP modulation of the wave intensity of EN and ELF/VLF emissions might be similar.