Amplitudes of Pc3 and Pc4 geomagnetic pulsations near the plasmapause projection (Kerguelen Observatory)

The daily behavior of the average amplitudes of Pc3 and Pc4 geomagnetic pulsations and its variations depending on the season and level of geomagnetic activity have been studied based on results of a spectral-temporal analysis of 3-year (1995-1997) continuous observations at Kerguelen subauroral observatory (Phi = 57.9degrees). It has been established that, under strongly disturbed conditions (SigmaKp > 25), maximums in the daily behavior of the average Pc3 and Pc4 amplitudes sharply shift from noon to morning and afternoon hours, respectively. In this case the average amplitudes of Pc4 pulsations depend on the season and level of magnetic activity, whereas the amplitudes of Pc3 pulsations mainly depend on the level of magnetic activity and slightly depend on the season. The distinguished differences in the dependence of the amplitude characteristics of Pc3 and Pc4 pulsations on the level of geomagnetic activity and season indicate that the primary sources of these pulsations are different, which apparently makes it impossible to combine them into one type of oscillations.