Ozone Hole Largest Since 2008

earth-stratosphereThe ozone layer is a layer of ozone gas around 20-30 km up in the stratosphere, and is of crucial importance in protecting life on Earth from harmful UV-B radiation from the sun. Every southern spring a large hole develops in this layer over Antarctica, however this year’s hole is the largest since 2008. How does the hole form and how important is this year’s growth?

Ozone is a gas consisting of three oxygen atoms in a molecule instead of the usual two. It is formed in the stratosphere when incoming ultraviolet radiation from the sun breaks up normal oxygen molecules (O2) into two single oxygen atoms. These atoms are very reactive and quickly react with another oxygen molecule to form an ozone molecule (O3).

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High Pressure Firmly In Charge This Week

Our fine and settled spell of weather continues this week as an intense area of high pressure refuses to shift. Hour after hour of long-awaited sunshine, tempered only by some wisps of high cirrus clouds and contrails. We could have done with this back during our real summer, but better late than never. But why does high pressure mean sunny weather?

Firstly, high pressure (anticyclones) usually means sunny weather, but not always. The reason for this will come later, but first we’ll look at why this one is giving us our sunniest spell since June. Continue reading

Irish Weather Online’s A-Z of Weather Terms

From our 2015 Autumn A-Z, a guide to some of the lesser-known terms used in meteorology.

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ABSOLUTE TEMPERATURE: temperature using the Kelvin scale. It is absolute because it is directly related to Absolute Zero and allows two temperatures to be directly compared.

ABSOLUTE ZERO (0 K): zero degrees on the Kelvin temperature scale. The lowest temperature possible, where all molecular motion stops.

ABSORPTION: the process by which radiation is absorbed by a substance, e.g. the air. Ozone absorbs harmful UV-C radiation while water vapour (H2O) and carbon dioxide (CO2) absorb longwave radiation (thereby causing the Greenhouse Effect).

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Our Atmosphere In Numbers

Our atmosphere. Image from NASA.

Our atmosphere is an envelope of gases surrounding the globe, extending up to a height of around 500 km. It is mostly made of nitrogen and oxygen, but also contains water-vapour, argon, carbon dioxide, ozone and others. It may seem uninteresting at first glance, but delving into it in a little detail can reveal some remarkable and unexpected findings.

The atmosphere is divided into several layers, as shown above. As it extends to around 500 km its volume is around 275 billion km3. Its density at sea-level is 1.225 kg/m3, decreasing exponentially to practically 0 at roughly 500 km.
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How Much Does A Cloud Weigh?

Cumulus mediocris cloud.  Image: Author
Cumulus mediocris cloud, around 1 km wide.
Image: Author

Clouds are visible suspensions of billions of tiny water droplets and/or ice crystals, and are formed when air rises and cools to its dewpoint, causing its water-vapour to condense out. You may wonder how a cloud can therefore remain suspended, given that it’s composed of water, but the reality is that each tiny particle acts independently, remaining suspended by the buoyant force of the air. But what if you were to measure the total weight of a cloud? What would it weigh? The answer is staggering, but not in the way you would expect!

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