(a) The monthly sunspot number (same as Fig. 2a). (b) The diurnal and seasonal variations of NmF2 from the Longyearbyen dynasonde as a function of UT and month of year. The magnetic noon and midnight are plotted in magenta and black horizontal lines, respectively. The green solid and dashed vertical lines present, respectively, the spring and autumn equinoxes. The solar elevation angles of 0° and 30° at 110 km altitude above Longyearbyen are overlaid by white curves. (c) The monthly NmF2 data around the magnetic noon (11–13 MLT, magenta), and magnetic midnight (22–01 MLT, black), as well as averaged over all local times (blue).