Example of an SIR event. Top panel: IMF and its z-component (black and blue solid lines, respectively). Middle panel: Proton number density and solar wind bulk speed. Bottom panel: Proton number density gradient. The red and green vertical lines delimit the SIR region and the fast solar wind stream (> 450 km/s), respectively. The brackets further indicate the SCSW (first red to first green vertical line) and FCSW (first green to second red vertical line).