Understanding the hot shallow layer above the earth surface

In summary, the temperature difference between the surface and the station is not as large as it could be due to the lower sun angle on a late fall day.
  • #1
Ardit
17
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In Wikipedia page of Diurnal Temperature variation, there is a statement as following: "As solar energy strikes the earth’s surface each morning, a shallow (1–3 cm) layer of air directly above the ground is heated by conduction. Heat exchange between this shallow layer of warm air and the cooler air above is very inefficient. On a warm summer’s day, for example, air temperatures may vary by 30°F from just above the ground to waist height."
First of all, do you believe it? And if you do, how comes that there is such a discrete temperature separation (a difference of up to 30°F) of these two layers (the 3 cm one and the one above it)?
 
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  • #2
It is definitely true. Haven't you ever seen reporters put a thermometer near the ground at a sporting event on a hot day?

The reason for the difference is that the sun is very efficiently heating the ground and the ground gets very hot.

I'm not sure I would agree that the steep gradient near the ground is a sign of inefficient heat transfer though: steeper gradients generally means faster and/or more efficient heat transfer.
 
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  • #3
The statement is indeed in the reference wiki gives, however there is no further reference.

Many years ago, I was involved in a small local experiment on our air base because we had concerns about temperature difference between station temperature and runway temperature during scorching hot days, as engine performance is a direct function of the air temperature. I remember that we had three temperature series, runway surface, at 1.5 meters and reported station temeprature. There was a difference of a few degrees between surface and station with the 1.5 meters some where in between, so not nearly as much as the syllabus suggests. But it may not have been hot enough.
 
  • #4
How did you measure the runway temp?
 
  • #5
I checked the surface temperatures of some hard surfaces outside, on what is a very clear day, with light wind:

White Concrete: 76F
Black Pavement: 91F

Air temperature under shade, 7' off the ground: 51F

Since it is late November, the sun is relatively low, even for 1PM, so this differential is a lot lower than it would be in the summer.
 
  • #6
russ_watters said:
How did you measure the runway temp?

I did not, I was merely observing the process. It was done however by the NLR way back in the 80's. But I realize it may not have been surface temperature but air temperature very close to the ground. I remember that there was a discussion that the difference was lower than expected.
 
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What is the hot shallow layer above the earth surface?

The hot shallow layer above the earth surface is known as the Earth's crust. It is the outermost layer of the Earth and is composed of solid rock that varies in thickness from approximately 5-70 km.

What causes the hot shallow layer above the earth surface to be hot?

The Earth's crust is hot due to the heat generated by the Earth's core and the decay of radioactive elements within the Earth's interior. Another factor that contributes to its heat is the trapping of solar radiation by the Earth's atmosphere.

How does the thickness of the hot shallow layer above the earth surface vary?

The thickness of the Earth's crust varies depending on its location. The thinnest crust is found under the ocean, while the thickest crust is found under mountain ranges. On average, the thickness of the Earth's crust is around 30 km.

What role does the hot shallow layer above the earth surface play in plate tectonics?

The Earth's crust is divided into large, moving plates that make up the Earth's surface. These plates float on top of the hot, liquid mantle and interact with each other, causing geological phenomena such as earthquakes and volcanoes.

How do scientists study and understand the hot shallow layer above the earth surface?

Scientists use a variety of methods to study and understand the Earth's crust, including seismology, remote sensing, and drilling. They also study the composition and properties of rocks and minerals found in the Earth's crust to gain a better understanding of its structure and evolution.

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