It’s become engraved in our brains to always have a jacket on hand whenever were planning on spending time outside at night, it’s just routine. Why do the temperatures almost always drop at night? The obvious answer is because the sun is no longer present to keep things warm, but this question and answer is too simple because there’s much more to it. The better question may be: how does the sun heat the air, and why are some nights much colder than others?
The sun heats the air by heating up the ground, and any object that the sun’s rays hit. Those objects then heat the air around them. At night, there is no energy from the sun to heat the Earth, so everything cools down. Because the sun heats the ground, places higher up in the atmosphere tend to stay near a constant temperature. In other words, high altitudes hardly change temperatures between night and day. Temperatures near the ground fluctuate the most, but sometimes these fluctuations are bigger and sometimes they are small.
This leads into the question of why some nights cool more than others, and why do some days warm more than others, assuming there is no changes in weather patterns. The reason for this is clouds! Clouds limit how much the temperatures can fluctuate. Just like insulation in your house, the clouds limit how much energy can travel through the atmosphere. During the day, the clouds prevent the sun’s energy from coming to Earth, which keeps us cooler. On the flip side, at night, clouds keep Earth’s energy from going into space. When there are no clouds, the energy can travel much more easily. This is why clear weather brings cooler nights and warmer days, while cloudy weather brings cooler days and milder nights. This fluctuation in daytime and nighttime temperatures is what is called the diurnal temperature range. This simply is a measure of how much the temperatures change over a 24-hour period, or one day. Cloudiness makes the diurnal temperature range smaller, and clear skies encourages a larger diurnal temperature range.
Whether or not clouds are present can have a huge affect on temperature ranges, but that’s not the whole story. There are many other factors that can affect diurnal temperature ranges, many of which are too complicated for this blogpost. Humidity, winds, and fronts can all affect the diurnal temperature ranges and how the temperatures fluctuate. But, when there is no active weather systems around, cloudiness is usually one of the dominant factors affecting the changes in temperatures from day to night.
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