polar stratospheric clouds play an important role in creating the ozone hole
the highest clouds on earth are about 80 km high
in the mid-latitudes most rain is cold rain, that means it leaves the clouds as ice and melts on the way down
pure water droplets without an aerosol inside (cloud condensation nucleus) freeze at about -40°C, sea salt aerosols make cloud droplets freeze at about -38°C, …
Clouds.
And there’s much more to be found.