ORLANDO, Fla. – The definition of winter varies depending on where you live. For Floridians, any time the temperature falls below 65 degrees, that’s winter-like weather. For other areas across the nation, that’s balmy.
Well, for people out west, numerous winter alerts are up with the potential for snow, ice and dangerous temperatures. I mean, below 32 degrees.
So, with the wintery weather comes the potential for a phenomenon called an inversion, or temperature inversion, which frequently happens during the colder months.
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But exactly what is it and why does it happen frequently during the colder months?
During normal weather conditions, air temperature decreases with distance from the Earth’s surface. Daytime heating happens when the sun heats up the surface, after which the heat then rises back into the air. As the warm air rises, it normally mixes with cooler air up above, resulting in a temperature gradient.
Temperature inversions happen when warm air above forms a cap over colder air below (near the surface) inverting the temperature gradient.
It happen frequently during the winter months because, as the sun sets, the air closest to the surface tends to lose daytime heat faster than the air above.
Mountainous terrain makes it more difficult for cold air near the surface to rise, so vertical mixing of air doesn’t happen. Due to the mountains, the cold dry air at the surface is trapped by moist warm air up above.
Over flat terrain, the resulting inverted temperature gradient returns to normal the following morning after the sun heats the ground and causes vertical mixing of the air layers.
However, in most mountainous areas, the sides of the surrounding mountains allow warmer air to flow upwards, resulting in a cap of warm air to form during the day.
If this cap forms high enough, clouds will form beneath it, fan out and block sunlight from reaching the ground during the day.
Without sunlight to warm up the air below, the inversion and cloud cover will persist.
Inversions also trap fine particles and pollutants in the lower cold layer because the upward movement of air is blocked off, preventing the dispersal of airborne contaminants.
This can pose a problem in cities with traffic congestion because the formation of inversions usually happens with rush-hour traffic and contributes to the formation of smog. People that have respiratory issues suffer from the pollutants being trapped until the cap is broken, allowing pollutants to mix out.
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