Two-dimensional histograms of varying proton versus 2.8–4.0. MeV electron intensities measured by STEREO-A/HET using one-minute data of the whole year of 2013. The plots show the logarithm of the intensities (excluding all zero intensities). The color scale (marking the number of observations in each bin) is logarithmic. The black solid line marks unity. The left, middle, and right panels show 13.6–15.1 MeV, 14.9– 17.1 MeV, and 17.0–19.3 MeV protons, respectively.