Figure 3
The points show the measured dip depths in the low cloud cover as one moves away from the magnetic Equator of the Earth (at the far right) towards the poles (at the far left). The sizes of the dips in the cosmic ray rates are indicated by the line labelled NM (for the neutron monitors used to measure them). The points should follow this line if ionization from cosmic rays causes a large part of the low cloud cover.
Image credit: Terry Sloan and Arnold Wolfendale, Environ. Res. Lett.