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Source : weather.gov

This is mentioned in the book I have been reading regarding stability in atmosphere. But I am not able to pin point exact reason behind this.

"As the layer subsides, it becomes compressed by the weight of the atmosphere and shrinks vertically. The upper part of the layer sinks farther, and, hence, warms more than the bottom part." (Ahrens et al.,2019)

-Ahrens, C.D., Henson, R. (2019). "Meteorology Today: An Introduction to Weather, Climate, and the Environment". 12th Edition. Chapter 6 ( Stability and Cloud Development), CENGAGE Learning Custom Publishing, page 146-147

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    $\begingroup$ I thougth the source of the text comes from the web link as the images, but it isn't. Please mention the book where the text comes to quote it correctly. $\endgroup$ – user12525 Jun 27 '19 at 10:30
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    $\begingroup$ I'm sorry as I used different sources for each. Although the image is found in both. Book is : Meteorology Today: An Introduction to Weather, Climate, and the Environment Textbook by C. Ahrens 11th Edition. Chapter 6 ( Stability and Cloud Development), page 146-147 $\endgroup$ – Maverick33 Jun 27 '19 at 10:39
  • $\begingroup$ @gansub Yes. I get it. But shouldn't there be uniform warming of the mass of sinking air in both upper and lower part. If it had to be uneven, then rather lower part should warm up more as pressure increases downwards and thus more compression. I don't understand the uneven distribution of warming and that too at upper layer. Am I making sense? $\endgroup$ – Maverick33 Jun 27 '19 at 12:47
  • $\begingroup$ @Maverick33 why would the lower layer warm ? Air temperature goes up as an air parcel sinks. But usually at night time there is radiational cooling. Or surface level cold air advection, etc. The important thing is convection is suppressed. $\endgroup$ – gansub Jun 27 '19 at 12:49
  • $\begingroup$ @gansub Why in the left image in the given question, the slope of the layer is not like that green-dotted line, rather it has rotated and upper part of x'-y' has more temperature than lower part. ( Even though same process of adiabatic compression is applied overall) $\endgroup$ – Maverick33 Jun 27 '19 at 12:49

I assume that the sentence in the book mainly refers to subsidence as an adiabatic process. This sinking motion has a maximum which is at a height well above the surface, simply for the reason that air flow can not penetrate the earth's surface. Therefore maximum adiabatic heating rates occur well above the surface as well. The precise height where this occurs depends on the height of the planetary boundary layer, which itself depends on many more both adiabatic and diabatic effects.


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