Fig. 1

Solar wind conditions from WIND as the background of the 17 March 2015 storm. The upper diagram shows variations in the magnetic field intensity (B), three components (Bx, By, and Bz), degree of fluctuations (rms divided by average B), solar wind speed, proton number density, the number density ratio of He⁺⁺ to proton, the proton temperature, and plasma beta based on protons. The lower is the vector diagram showing projections onto X–Y, X–Z, and Y–Z planes of the 20-minute averaged magnetic field vectors. The magnetic cloud interval is indicated by two vertical solid lines. The dashed line marks the shock arrival time. The red curves depict the optimum result of fitting with a toroidal flux rope model