Pitch-angle distribution function of solar wind electrons. (a) Pitch angle distribution of solar wind electrons with energies between 69 eV and 5 keV, for the time interval from 09:00 on 2022 January 19 to 18:00 on January 20. (b), (c), and (d) are 2D speed, pitch-angle distributions averaged over the three selected 70 minutes intervals, marked by the magenta shadowed regions in panel a.