Plane polarization is one of the optical effects that account for the appearance of rainbows.
Plane polarization, also known as linear polarization, is a characteristic of electromagnetic waves, including light.
When an electromagnetic wave is plane polarized, the electric field remains fixed in a particular direction as the wave propagates. As a result, the light oscillates on a single plane, hence the name.
The polarization of light in rainbows contributes to the vividness and intensity of the colours we see.
The light that produces rainbow effects is typically 96% polarized. This means that:
Observed light exiting a raindrop is polarized on a plane bisecting each droplet and tangential to the arcs of the rainbow.
The presence of other atmospheric phenomena, such as water droplets of varying sizes or ice crystals, can affect the amount of plane polarization and so influence the appearance of rainbows.