In addition to affecting how radio waves propagate here on Earth, the ionosphere is also the layer of the atmosphere where the aurora borealis and aurora australis (also called the northern and southern lights) happen. The aurora are produced when electrons and protons trapped in Earth's magnetosphere (the region of outer space where we can measure Earth's magnetic field) precipitate (or rain down on) the Earth's atmosphere and excite oxygen atoms and nitrogen atoms and molecules, causing them to emit the green, red, and sometimes blue and purplish light we see as the aurora. Aurora are also associated with huge electrical currents in Earth's magnetosphere that flow down into the ionosphere during geomagnetic storms and auroral substorms.
The trapped plasma (or gas of electrons and ions) that fills Earth's magnetosphere comes from two sources - the solar wind and outflows from the ionosphere during geomagnetic storms. One of the scientific topics I am studying is electromagnetic ion cyclotron (EMIC) waves observed by satellites orbiting the Earth. These waves occur in three frequency bands, a hydrogen or proton band, a helium band, and an oxygen band. The oxygen EMIC waves are not observed very often because the oxygen ions needed to produce EMIC waves in space may come from the ionospheric outflows during big geomagnetic storms.
The ionosphere also has interesting interactions with lightning. You are probably used to seeing lightning that travels between clouds or between the clouds and the ground during thunderstorms. However, there are other forms of lightning that were not discovered until very recently thanks to high-speed cameras. Sprites, jets, and ELVES travel upwards towards the ionosphere from thunderclouds, and they are not completely understood. Lightning can also perturb the ionosphere to generate a type of plasma wave called a whistler. People can hear whistler waves in radio signals, and satellites orbiting the Earth also observe them in space. You can listen to the sounds of whistler waves at Earth and Jupiter and other space sounds here -
http://www-pw.physics.uio.../space-audio/sounds/