Tracking preliminary impulse propagation using the Heliophysics System Observatory, SuperMag and Intermagnet ground-based magnetometer stations

The preliminary impulses are probably the first signal of a dynamic pressure pulse's (DPP) propagation in the magnetosphere. They are observed at ground-based magnetometer stations as small changes in the magnetic field before the main compression occurs. However, despite being easily spotted in most of the observations after a DPP, their mode of propagation is still under discussion. Currently, there are two popular explanations about their propagation. The first is that impulses propagate through the Earth-ionosphere waveguide, which implies an almost simultaneous observation of the impulse around the Earth. The second explanation suggests an MHD wave mode of propagation that implies slower propagation and a more observable delay between stations. In this study we use the recently available 1-second resolution data from ground-based magnetometers through SuperMag, Intermagnet data, and the Heliophysics System Observatory to determine the impulse propagation in magnetic latitude and longitude, by focusing in specific events with strong DPP and northward Interplanetary Magnetic Field conditions.