When we turn our face towards the sun on a day with clear skies: Is the heat we feel on our skin actual heat radiation from the surface of the sun or do we just feel the warmth of the molecules in our atmosphere which have been “warmed” by radiation from the upper atmosphere?
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There are many types of radiation and the one you just described is called thermal radiation. Energy from the sun that has been let off as heat traveling through space hit your face, kicking your can all over the place.
The air around you is more or less all the same temperature. Turning to face the sun and feeling an immediate warmth is heat delivered by the light from the sun. This is pretty easy to test, too, by moving in and out of shadows and feeling the difference.
There are many types of radiation and the one you just described is called thermal radiation. Energy from the sun that has been let off as heat traveling through space hit your face, kicking your can all over the place.
The air around you is more or less all the same temperature. Turning to face the sun and feeling an immediate warmth is heat delivered by the light from the sun. This is pretty easy to test, too, by moving in and out of shadows and feeling the difference.
You are feeling the thermal radiation from the sun. The air around you is generally wanted by the long wave radiation that has been reflected by the earth’s surface back into the atmosphere. Short wave incoming solar radiation only gets absorbed by the atmosphere at very specific wavelengths, some gets reflected or scattered by clouds, aerosols and water vapour while the rest hits the Earth’s surface (or your face)
Both, kind of. Let’s unpack that.
First fact to know – heat flows from warmer body to colder body.
Second fact: There are 3 ways to transfer heat: radiation, conduction, and convection. Conduction is flow of heat through the material. Not relevant here. Convection is transfer of heat between a surface of an object and the surrounding fluid (i.e. transfer from your body to air or vice versa), and radiation is heat transfer via electromagnetic waves.
When you’re standing in the sun, you’re being warmed directly by actual radiation from the sun.
Additionally, you’re feeling the heat, not from the atmosphere, but from your own body. Your body is at 37°C. A warm summer day is, say, 30°C. That means air is colder, and heat actually transfers from your body to the air. You’re giving heat to the air. But, since your body is constantly producing heat due to various biochemical processes, the warmer the air is, the less heat you’re able to dissipate (because the speed of heat transfer depends on the difference in temperatures), the warmer you feel.
So, TLDR, you’re being warmed by the sun and by your own body.
Btw., a practical application of your question – because the sun has the ability to directly heat up objects on Earth, that’s the reason why, if you want to measure air temperature, you put the thermometer in the shade, not on direct sun. You want to measure how warm the air is without adding in additional heat from the sun.
You are feeling the thermal radiation from the sun. The air around you is generally wanted by the long wave radiation that has been reflected by the earth’s surface back into the atmosphere. Short wave incoming solar radiation only gets absorbed by the atmosphere at very specific wavelengths, some gets reflected or scattered by clouds, aerosols and water vapour while the rest hits the Earth’s surface (or your face)
Both, kind of. Let’s unpack that.
First fact to know – heat flows from warmer body to colder body.
Second fact: There are 3 ways to transfer heat: radiation, conduction, and convection. Conduction is flow of heat through the material. Not relevant here. Convection is transfer of heat between a surface of an object and the surrounding fluid (i.e. transfer from your body to air or vice versa), and radiation is heat transfer via electromagnetic waves.
When you’re standing in the sun, you’re being warmed directly by actual radiation from the sun.
Additionally, you’re feeling the heat, not from the atmosphere, but from your own body. Your body is at 37°C. A warm summer day is, say, 30°C. That means air is colder, and heat actually transfers from your body to the air. You’re giving heat to the air. But, since your body is constantly producing heat due to various biochemical processes, the warmer the air is, the less heat you’re able to dissipate (because the speed of heat transfer depends on the difference in temperatures), the warmer you feel.
So, TLDR, you’re being warmed by the sun and by your own body.
Btw., a practical application of your question – because the sun has the ability to directly heat up objects on Earth, that’s the reason why, if you want to measure air temperature, you put the thermometer in the shade, not on direct sun. You want to measure how warm the air is without adding in additional heat from the sun.
The warmth you feel from the sun is from the visible light hitting your skin, your skin absorbing some of that energy, then re-radiating it as longwave IR (heat). In fact, practically all the warmth on the planet is the result of visible light being converted into longwave IR. The sun doesn’t put out enough longwave IR to heat the planet at our distance.
What thermal radiation from the sun we receive is mostly absorbed by the upper atmosphere before it reaches the surface. Thanks to greenhouse gases, our atmosphere is relatively opaque to longwave IR so incoming radiation is pretty well taken care of long before it makes it to the lower part of the atmosphere.
For more information, look up black body radiation.
The warmth you feel from the sun is from the visible light hitting your skin, your skin absorbing some of that energy, then re-radiating it as longwave IR (heat). In fact, practically all the warmth on the planet is the result of visible light being converted into longwave IR. The sun doesn’t put out enough longwave IR to heat the planet at our distance.
What thermal radiation from the sun we receive is mostly absorbed by the upper atmosphere before it reaches the surface. Thanks to greenhouse gases, our atmosphere is relatively opaque to longwave IR so incoming radiation is pretty well taken care of long before it makes it to the lower part of the atmosphere.
For more information, look up black body radiation.
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