O
The terms and definitions found in the glossary relate to the science of meteorology.
For descriptions and definitions of words used in the Bureau's forecasts and warnings, please refer to Weather Words.
- Occluded Fronts
- See Fronts (Occluded).
- Offshore
- The coastal waters zone between 12 and 60 nautical miles from the coast.
- Oxygen
- The second most abundant gas in air, comprising 21% by volume. It is a colourless and odourless gas.
- Ozone
- One of the several gases that make up the Earth's atmosphere. It is the triatomic* form of oxygen and makes up approximately one part in three million of all of the gases in the atmosphere. If all the ozone contained in the atmosphere from the ground level up to a height of 60 km could be assembled at the earth's surface, it would comprise a layer of gas only about 3 millimeters thick, and weigh some 3000 million tonnes. Ozone is toxic at high concentrations because it reacts strongly with other molecules.
* Each ozone molecule is made up of three oxygen atoms.