Above the stratosphere is the mesosphere and above that is the ionosphere (or thermosphere), where many atoms are ionized (have gained or lost electrons so they have a net electrical charge). The ionosphere is very thin, but it is where aurora take place, and is also responsible for absorbing the most energetic photons from the Sun, and for reflecting radio waves, thereby making long-distance radio communication possible.
[Perhaps add a Shockwave animation of the ionosphere with aurora, absorption of photons from the Sun, and/or radio waves reflecting? Or maybe replace present image shown by "Layers" button with an animation which also includes some or all of these?]