The Hottest And Coldest Time Of The Day – When They Occur And Why
The warmest time of the day is when the Earth receives the most solar radiation from the sun, and it is closest above your location, correct? Actually, no. Though it sounds obvious, you will be off by a few hours.
The same applies to the coldest part of the day. Both the hottest and coolest part of the day occur much later than you may think.
It does not seem to make sense since the Earth receives the most amount of solar radiation from the sun around noon (depending on your location and the time of year.)
Similarly, the surface will keep on cooling down during the night until sunrise, when it starts to receive sunlight and begins warming up. It is natural to reason, therefore, that the coldest time of the day will be just before sunrise. But this is not the case.
This article examines when the warmest and coldest part of the day is and why they occur at these different times. It also looks at the various factors involved in these occurrences.
Hottest Time Of The Day
As already mentioned, the Earth's surface receives the most amount of solar radiation around noon, yet this is not the part of the day that is the warmest.
Before we look into why this occurs, it is important to define a clear definition first of when precisely the hottest part of the day is:
What Is The Hottest Time Of The Day?
The hottest time of the day occurs between 3 pm and 4:30 pm, 3-5 hours after noon (when the sun is at its highest point in the sky). This delay is due to the Earth's surface receiving and absorbing heat at a higher rate than it can radiate until mid to late afternoon when the process reverses.
Although this summary is an accurate average to use to judge when a day will be at its warmest, a couple of factors can cause the actual peak temperature to occur earlier or later in the afternoon.
Weather elements such as cloud cover and wind can have a significant impact on peak daily temperatures. Geographical location also has an effect, where inland regions can reach their highest temperatures of the day much later in the afternoon than coastal areas.
Why The Hottest Time Of Day Occur In The Afternoon
Although the sun is at its highest point in the sky and the Earth receives the most amount of solar radiation around noon, we now know that the day's highest temperature does not occur until around 3 pm. This delay is also known as Thermal Response.
Thermal response occurs as follows: After noon, even though the sun's radiation starts to drop, the Earth retains much of its heat while still receiving solar radiation. It means the heat building at the surface is higher than that which the planet can radiate away.
As a result, the temperature continues to rise until the solar radiation is weak enough for the Earth's ability to radiate heat back into the atmosphere, becomes greater than the radiation it receives. And this occurs between 3 pm and 4:30.
Coldest Time of the Day
Like the hottest time of the day, the coldest time of the day occurs much later than one might expect. What makes it even more confusing is the fact that weather forecasters often refer to daily lows that will be experienced "during the evening."
It is statements like these that back up the common belief that the coolest time of day should occur during the night. As much as this type of thinking seems to make sense, it is not accurate at all.
As is the case with the warmest time, it is important to define when precisely the coldest time of day is first before we delve into explaining why and how this takes place:
The Coldest Time of the Day
The coldest time of the day occurs some time after sunrise.
It occurs when the sun's radiation is still too weak to warm the planet's surface at a greater rate than the Earth is radiating heat away from the surface into the atmosphere.
This may not seem to make sense at first since solar radiation is the primary source of heat and light to the Earth every day.
Take into consideration, though, that when we perceive the sun to rise on the horizon, it is still 6 degrees below the horizon (aka twilight). The atmosphere can bend light like a lens, making it appear that we receive sunlight when no actual solar radiation is yet present.
Depending on your location and time of the year, after sunrise, it will also still take the sun between 3 and 8 hours to reach its highest point in the sky and the Earth to receive maximum solar radiation after sunset.
Although these are all contributing factors, the main reason for the coldest time of the day involves the same factors responsible for the warmest part of the day, which we will address in the next section.
Why The Coldest Time Of Day Occur After Sunrise
After the hottest time of the day, which occurs around 3 pm, the Earth continues to radiate heat out into the atmosphere at an accelerated pace. At the same time, solar radiation decreases until completely disappearing around sunset.
The planet's surface continues to cool down as it radiates heat throughout the night. After sunrise, the ground starts to receive solar radiation, but it is still too weak to counteract the rate at which the surface continues to cool down as it radiates heat into the atmosphere.
The coldest time of the day occurs once the speed at which the Earth radiates heat is no longer greater than the incoming solar radiation, and the ground starts to warm up. As already stated, this occurs some time after sunrise.
The exact time the coldest stage of the day takes place depends on atmospheric conditions, as well as the location and the time of the year.
Although it may not have made sense in the beginning, it should now be clear why the hottest and coldest times of the day occur when they do. It also explained why the delay between the period of maximum solar radiation and the hottest time of the day takes place.
This delay occurs on a seasonal basis as well. The warmest and coldest days of the year (and the hottest and coldest months) are based on the same principle. To find out more about these occurrences, you can find the in-depth article here.
This article aimed to examine when the warmest and coldest part of the day is and why they occur at these times. It also looked at the various factors involved in these occurrences.
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Until next time, keep your eye on the weather!