An analysis of Sudden Impulses at geosynchronous orbit

An analysis of sudden impulses (SI) at geosynchronous orbit (2000–2004) confirms a general dependence of the SI amplitude on the variation of the square root of the solar wind pressure, together with an explicit LT dependence, with greater responses at satellites located closer to noon meridian. In the dayside hemisphere the magnetospheric response, which mostly influences the Bz component, is well consistent with the magnetic field jump expected for changes of the magnetopause current alone, driven by changes of the solar wind pressure. In the dark hemisphere, where the changes of the Bx component are often relevant, the competing contributions of several current systems (from the magnetopause, cross-tail current, ring current, Birkeland current) determine a large variety of responses that cannot be interpreted in a statistical sense. Depending on the solar wind conditions, different situations emerge for nightside events. We present a case in which a remarkable magnetospheric compression determined field variations which can be interpreted in terms of a strongly dominant contribution of the magnetopause current even in the midnight sector, while in other cases the observed features are consistent with the predictions of the global current system. We also speculated that additional elements (such as the geocentric distance of the hinging point, the separation point between closed and open field lines in the geomagnetic tail) might play a crucial role in determining the aspects of the magnetospheric response. The correspondence between model predictions and observations persists even in cases of moderate Southward IMF component