Polar Stratospheric Clouds over Scotland | Earth Science

Polar Stratospheric Clouds over Scotland | Earth Science

Noctilucent clouds, also known as polar mesospheric clouds, form in a part of the atmosphere roughly 50 to 86 kilometers (30 to 54 miles) above the surface of our planet. Their high altitude allows them to reflect sunlight after the Sun has set. These night-shining, or noctilucent, clouds long puzzled the researchers that studied them. They wondered how they formed. The clouds’ behavior has become more mysterious over the past two decades as the clouds have begun to shine more brightly and to appear at lower latitudes than they did before.

Scientists recently discovered that polar stratospheric clouds, long known to play an important role in Antarctic ozone destruction, are occurring with increasing frequency in the Arctic. These high altitude clouds form only at very low temperatures and help to destroy ozone in two ways. They provide a surface that converts benign forms of chlorine into reactive, ozone-destroying forms, and they remove nitrogen compounds that moderate the destructive impact of chlorine. In recent years, the atmosphere above the Arctic has been colder than usual, and polar stratospheric clouds have lasted longer. As a result, ozone levels have been decreasing.

NASA Ozone Watch:

https://ozonewatch.gsfc.nasa.gov

Ozone is a gas made up of three oxygen atoms (O3). It occurs naturally in small (trace) amounts in the upper atmosphere (the stratosphere). Ozone protects life on Earth from the Sun’s ultraviolet (UV) radiation. In the lower atmosphere (the troposphere) near the Earth’s surface, ozone is created by chemical reactions between air pollutants from vehicle exhaust, gasoline vapors, and other emissions. At ground level, high concentrations of ozone are toxic to people and plants.

Ninety percent of the ozone in the atmosphere sits in the stratosphere, the layer of atmosphere between about 10 and 50 kilometers altitude. The natural level of ozone in the stratosphere is a result of a balance between sunlight that creates ozone and chemical reactions that destroy it. Ozone is created when the kind of oxygen we breathe—O2—is split apart by sunlight into single oxygen atoms. Single oxygen atoms can re-join to make O2, or they can join with O2 molecules to make ozone (O3). Ozone is destroyed when it reacts with molecules containing nitrogen, hydrogen, chlorine, or bromine. A portion of the molecules that destroy ozone occur naturally, but people have created others.

Image Credit: Alan Tough

Caption Credit: NASA

Image Dates: Dec. 19-24, 2023

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