The colorful clouds near the top of this picture are Polar Stratospheric Clouds (PSCs). The PSCs are flying high above the darker cirrus clouds at the bottom of the picture. This photo was taken from a jet airplane.
Click on image for full size
Image courtesy of NASA (Paul Newman, GSFC).

Polar Stratospheric Clouds

The stratosphere is a layer of Earth's atmosphere. We live in the troposphere, the layer below the stratosphere. There are many different kinds of clouds in the troposphere. However, there is only one kind of cloud in the stratosphere! Those clouds are called Polar Stratospheric Clouds (PSCs).

PSCs only form when it is really, really cold. They are mostly seen in the winter near the North or South Pole. They form way high up in the stratosphere where the temperature is colder than -78° C (-108° F). PSCs are about 15 to 25 km (about 9 to 16 miles) above the ground.

We live in the troposphere. There is lots of water vapor in the air in the troposphere. That's why we have lots of clouds here. The clouds are made of tiny water droplets or small ice crystals. The stratosphere is different. It is very dry. There are not many clouds there. Some PSC clouds are made of water ice crystals, like "normal" clouds. Other PSCs have nitric acid and sulfuric acid in them!

PSCs are usually very colorful. Ice crystals in the clouds break sunlight up into different colors. People often see PSCs around sunrise or sunset.

PSCs can cause trouble. They help create the ozone hole. The ozone layer protects us from ultraviolet radiation in sunlight.

PSCs may help us too. They might warn us about global warming. Global warming heats air near the ground in the troposphere. However, global warming cools down air in the stratosphere. Remember, PSCs need really cold temperatures. Maybe there will be more PSCs in the future if the stratosphere gets colder. Scientists are watching carefully to see.

Last modified February 27, 2009 by Randy Russell.

You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

How Clouds Form

A cloud is composed of tiny water droplets or ice crystals. A series of things have to happen in order for these water droplets or ice crystals to form into clouds in the atmosphere, and different types...more

Nitric Acid - HNO3

Nitric acid is a very strong kind of acid. If you got some on your skin, it would burn you! Nitric acid has nitrogen, oxygen, and hydrogen atoms in it. Earth's atmosphere has a very, very tiny bit of nitric...more

Sulfuric Acid - H2SO4

Sulfuric acid is a very common type of acid. Acid rain has sulfuric acid in it. Acid rain harms plants, fish, and other living things. A type of air pollution causes acid rain. When people burn fossil...more

Global Warming: Scientists Say Earth Is Heating Up

Earth’s climate is getting warmer. During the past 100 years Earth’s average temperature rose about 0.6° Celsius (1.0° F). Things that people are doing like burning fossil fuels, changing the way land...more


Altocumulus clouds are part of the Middle Cloud group. They are grayish-white with one part of the cloud darker than the other. Altocumulus clouds usually form in groups. Altocumulus clouds are about...more


Altostratus clouds belong to the Middle Cloud group. An altostratus cloud usually covers the whole sky. The cloud looks gray or blue-gray. The sun or moon may shine through an altostratus cloud, but will...more


Cirrocumulus clouds belong to the High Cloud group. They are small rounded puffs that usually appear in long rows. Cirrocumulus are usually white, but sometimes appear gray. Cirrocumulus clouds are the...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA