Asymptotic viewing directions of the GMDN and MD + NM at Syowa Station. Each small symbol shows the asymptotic direction of primary GCR having the median primary rigidity (P_m) observed in each directional channel of GMDN and Syowa MD. Each large solid symbol indicates the viewing direction of the vertical channel in each MD, while a large cross symbol indicates a viewing direction of Syowa NM. The track through each solid symbol represents the spread of viewing directions corresponding to the central 80% of the rigidity response.