The magnetosphere of the earth undergoes oscillations of different periods and amplitudes. There is almost consensus that the variations are of solar origin, while the earth’s main magnetic field and secular variations are of internal origin. The magnetospheric (ULF) pulsations can arise from a variety of sources, and these pulsations are often observed to occur at discrete frequencies over extended intervals of time. The free energy needed to stimulate such pulsations can arise from local reconfiguration of magnetic stresses, wave-particle interaction, or a host of other sources which are internal to the magnetosphere. In addition, the solar wind can often provide a source of broadband energy which can then couple to discrete magnetospheric oscillations. Knowing that the real solar wind is variable, impulsive compression arising from rapid increase of solar wind dynamic pressure requires changes of the plasma and field properties through the magnetosphere. The present work studies the source of magnetospheric ultra low frequency pulsation focusing on the solar wind dynamic pressure and solar wind number density as a direct driver of these pulsations. The correlation between the solar wind number density pulsations and the magnetospheric magnetic field oscillations was studied for 30 events (in the interval from January to June 2007). The spectral analysis of the solar wind number density and the geosynchronous magnetospheric data was also investigated for the same events. Both investigations revealed a strong relation between the global magnetospheric oscillations and the solar wind oscillations. Keywords: Magnetosphere, Magnetospheric oscillations, Solar wind , interplanetary magnetic field.
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