The adjacent animations simulate the variation by month of the ionosphere for two different years:

1. The year 1990 (upper image), which was a period of high solar activity with many (150) sunspots.
2. The year 1996 (lower image), which was a period of low solar activity with few (10) sunspots.

The plots show electron density contours, which are an indication of the amount of ionization in the atmosphere. Yellows and reds indicate larger ionization and blues and greens indicate smaller ionization. Notice the substantial differences in these two animations, with much stronger atmospheric ionization in the upper image (the active Sun of 1990) than the lower image (the quiet Sun of 1996).