Polar stratospheric clouds
Also called: Nacreous clouds · Topic: Atmosphere: Composition, Structure and Elements of Weather · NCERT: Beyond NCERT
Meaning
Polar stratospheric clouds form in the stratosphere over the poles during the dark polar winter, when temperatures fall below about −78°C. Chemical reactions on the surfaces of these clouds free chlorine from CFCs and other ozone-depleting chemicals. When sunlight returns in spring, this chlorine destroys ozone again and again, which creates the ozone hole. They form far more often over Antarctica, because the southern polar vortex (a ring of strong winds around the pole) is colder and steadier.
Example
Over Antarctica, these clouds form each winter. Then from September to October, as the Sun returns, the ozone hole opens over the continent.
Don't confuse with
- Noctilucent clouds: these form much higher, near the mesopause (about 80 km), in polar summer. They do not destroy ozone.
Related concepts
- Ozone layer
- Dobson unit
- Ozone hole
- Montreal Protocol
- Kigali Amendment
- Stratospheric aerosol injection