The Manifestation of Sudden Impulses and the Role of the Magnetospheric Current Systems.

Abstract:

The amplitude of the Sudden Impulses in the magnetosphere is known to be related to the variation of the square root of the solar wind dynamic pressure, ΔP^1/2, typically associated with fronts of solar wind transient, such as shock waves. Nevertheless, at geostationary orbit, the normalized response (ΔB_z/ΔP^1/2) of the vertical component (whose jump is often accompanied by a variation of the radial component, B_x, as well) reveals, in each local time sector, a large variability which may depend on several factors, such as the external solar wind and interplanetary magnetic field conditions, the state of the magnetosphere, the position of the impact point of the solar wind front on the magnetosphere boundaries, the magnetopause motion, etc. We analyze these aspects, considering also the seasonal effects which modulate the orientation of the Earth’s dipole with respect to the Sun-Earth direction. Following our previous investigations, we also compare the magnetospheric response with model predictions, as evaluated in terms of the concurring contribution of the magnetospheric current systems (from the magnetopause, the ring current, the cross-tail current) in order to ascertain the role and the onset time of each current. A careful identification of these aspects is also useful to discriminate between magnetospheric and ionospheric contributions in the ground manifestation of such events.