Statistical properties of flux closure induced by solar wind dynamic pressure fronts

We present a statistical study of flux closure intervals induced by solar wind dynamic pressure fronts. We consider that a dynamic pressure front reaches the Earth when a dayside subauroral proton flash is observed in the SI2 channel of the IMAGE-FUV experiment. This pragmatic criterion selects both weak and strong pressure fronts. It is found that the preconditioning of the magnetosphere prior to the pressure pulse arrival mainly governs the magnetospheric response to a weak solar wind dynamic pressure front. This preconditioning includes the amount of open magnetic flux available in the magnetosphere prior to the pressure front arrival and the size of the magnetospheric cavity. However, in the case of a strong pressure pulse, the magnetospheric response is more sensitive to the solar wind properties characterizing the dynamic pressure front. The pressure jump is not the only one important, but also the variation of the solar wind velocity and IMF magnitude. In overall terms, we find that a strong dynamic pressure front is typically characterized by a dynamic pressure increase larger than Ë 2.8 nPa that takes place on timescales of the order of a few minutes.