Type 1 example. Decrease observed by Helios 1 during an IMC passage on January 1975. From top to bottom: density, temperature, solar wind speed, magnetic field components, the 3.77–12.72 MeV proton channel, and the 1.69–3.68 MeV/n alpha channel from the cosmic ray experiment (E6), normalized count rate in A and C detectors and magnetic field strength. Vertical lines mark the shock position (dotted line) and MC boundaries (solid lines) and the overplotted solid lines in fourth panel are the fit lines from the MC model.