Breakdown: Why temperature is key in frost formation
MEMPHIS, Tenn. (WMC)- Frost can be annoying especially if you have to scrape it off your windshield in the morning. This breakdown will be about why frost forms and how we can keep it off of our windshields.
Let’s start with what it is. Frost is water droplets in the air that is deposited onto a surface as ice.
Frost usually forms when a surface cools through a loss of infrared radiation to a temperature which is colder than the dew point of the air next to the surface, and the temperature of that surface is below freezing. The moisture comes from water vapor in the air.
The cooling of the air overnight near the ground causes morning frost on grass and car windshields. Frost will only form on a surface if the temperature is at or below freezing. Sometimes you may notice that the temperatures are above freezing when frost is formed. This is because the air temperatures are usually taken at about four feet above the ground, where it can be warmer than temperatures at ground level.
Frost forms mostly on objects close to the ground. The best conditions for frost formation are a clear sky, calm wind, high humidity and below freezing temperatures.
There are several types of frost, but the most common is radiation frost. This is the type of frost that you see on the ground and on your car’s windshield.
In addition, advection frost forms when cold wind moves over a moisture-rich surface, such as grass or plants. This frost can have a spiked appearance.
You may have notice that at times, frost forms in an open field but not under a tree. This is because trees put out more radiation toward the ground than does the clear sky. The energy lost at the ground under the tree is less than that of the grass in the open field. The grass in the open field cools faster and reaches the frost point before the grass under the tree.
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