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Sydney smoke explained
Ben Domensino, Friday October 21, 2016 - 10:18 AEDT
Smoke blanketing Sydney this morning gave a face to a typically invisible phenomenon in our atmosphere, known as a temperature inversion.
Most of the time, air temperature decreases as you move upwards through the lower portion of our atmosphere (which is called the troposphere). If you go up far enough, it gets so cold that water droplets in clouds turn into ice.
If this standard temperature pattern in the lower troposphere is flipped upside down, warm air sits on top of cooler air and traps it near the ground. This is called a temperature inversion.
Inversions most commonly happen at the end of a calm and clear night. These conditions allow heat from the previous day to radiate away from the surface into space. This causes the ground to lose heat so quickly that air near the surface cools down faster than the air above it, creating an inversion.
Temperature inversions are not uncommon and can occur at any time of year. However, they are usually invisible.
On rare occasions, smoke or fog can become trapped in the layer of cool air below an inversion, allowing us to witness the spectacle.
This was the case in Sydney this morning. Smoke from controlled burns around the Sydney Basin became trapped under a temperature inversion sitting at about 600 metres above sea level. Below this height it was smoky, but above it the air was clear.
Air quality in parts of Sydney this morning was reduced to hazardous levels by the smoke and those living away from the coast were worst affected.
As the temperature at the surface warms up today, the inversion will be broken and smoke will mix into the atmosphere, allowing it to clear across the Sydney Basin.
Rain falling across Sydney tomorrow morning will prevent it from being another smoky start.
- Weatherzone
© Weatherzone
2016
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