Why, at lower altitudes, does the atm change more rapidly?

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In summary, the atmospheric pressure changes more rapidly with decreasing altitude due to the weight of the air column above exerting more pressure on the air below. This is not a linear relationship and is better explained through the adiabatic case rather than the isothermal case.
  • #1
Bipolarity
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The lower the altitude, the more rapidly the atmospheric pressure changes with respect to altitude.

http://www.microwaves101.com/encyclopedia/images/powerhandling/Pressure2.jpg [Broken]

Why does this happen? I know that the pressure itself is supposed to decrease since the weight of the air column increases as altitude drops, but shouldn't this be a linear relation?

Does it have anything to do with the air density and the convection of air?

Thanks!

BiP
 
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  • #3
Borek said:

That's the isothermal case but the troposphere is rather adiabatic:

[itex]p = p_0 \cdot \left( {1 - \frac{{\kappa - 1}}{\kappa } \cdot \frac{{M \cdot g}}{{R \cdot T_0 }} \cdot h} \right)^{\frac{\kappa }{{\kappa - 1}}}[/itex]
 
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  • #4
It shows why the dependence is not linear without delving into too many confusing details. Much better from the pedagogical point of view.
 
  • #5
A rather simplistic but intuitive way to see why it should not be linear is this:

Examine the graph in your OP and imagine it as a straight line. It would intersect the X-axis (altitude).

It would mean that the edge of space -the line between atmosphere and vacuum - would be sharp. You could be at 120,000 feet and be in atmo, and then at 121,000 feet and be in hard vacuum.

Does that make sense?
 
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  • #6
DaveC426913 said:
Does that make sense?

Why not?
 
  • #7
DrStupid said:
Why not?

Why not what? Why does it not make sense?

I think most people intuitively know that there is no hard boundary at very the edge of the atmo - that it gets tenuous the farther out you go.

I'm pointing out that, knowing this, one can immediately deduce that the graph must be curved.
 
  • #8
Thank you everyone for your replies. I understand it now.

BiP
 
  • #9
DaveC426913 said:
I think most people intuitively know that there is no hard boundary at very the edge of the atmo - that it gets tenuous the farther out you go.

I'm pointing out that, knowing this, one can immediately deduce that the graph must be curved.

The adiabatic graph also intersects the X-axis although it is curved and even for a linear pressure gradient there would be no hard boundary. Therefore I can not see the logic in your argumentation. The explanation in Borek's link is much more better. The calculation is made for an isothermal case but the same principle works for a non-isothermal atmospheres too.
 
  • #10
DrStupid said:
The adiabatic graph also intersects the X-axis although it is curved and even for a linear pressure gradient there would be no hard boundary.
If it intersects the axis then that means at one point there is pressure, and at a point an arbitrarily-small distance away the pressure is zero - no air. That's a boundary.

Most us can intuitively grasp that this is not the way the atmo tapers off. Once the OP realizes that he already knew the pressure gradient was curved, he would realize that it's probably curved all the way to the ground.

It's the difference between being told something, and self-discovery.

DrStupid said:
The explanation in Borek's link is much more better.
It's not a competition. Multiple responses are not penalized. :rolleyes:
 
  • #11
Solving differential equation with ideal gas law and P=ρgh you would see that it follows an exponential pattern which coincides with your graph.

I think an intuitive explanation would be, with decreasing altitude, more weight of the air above is exerted to the air below.
 
  • #12
DaveC426913 said:
If it intersects the axis then that means at one point there is pressure, and at a point an arbitrarily-small distance away the pressure is zero - no air. That's a boundary.

Its not a hard boundary because for arbitrarily-small distances the corresponding pressure differences would be arbitrarily-small to.

DaveC426913 said:
Most us can intuitively grasp that this is not the way the atmo tapers off.

Trying to understand physics intuitively is sometimes not a good idea. An adiabatic atmosphere would taper off this way and it is more realistic than the isothermal case described by the exponential curve without boundary. Explaining why the real atmosphere has no upper limit is not as easy as you seem to believe. The pressure gradient depends on the temperature profile and that's a quite complex topic in the upper atmosphere.
 

1. Why does the atmosphere change more rapidly at lower altitudes?

Atmospheric pressure and density decrease with increasing altitude. This means that there is less air molecules at higher altitudes, resulting in a thinner atmosphere. Therefore, any changes in temperature, humidity, and air density will have a larger impact on the atmosphere at lower altitudes.

2. How does temperature affect the rate of change in the atmosphere at lower altitudes?

Temperature plays a crucial role in determining the atmospheric conditions. At lower altitudes, the air temperature is relatively warmer, causing air molecules to move faster and creating more collisions and mixing. This leads to a more rapid change in the atmosphere compared to higher altitudes with colder temperatures.

3. Does the topography of the land have an impact on the rate of change in the atmosphere at lower altitudes?

Yes, the topography of the land can affect the rate of change in the atmosphere at lower altitudes. For example, mountain ranges can create barriers for air flow, causing air to rise and cool, resulting in changes in temperature and precipitation. This can lead to variations in the atmosphere's composition and properties.

4. How does the Earth's rotation influence the rate of change in the atmosphere at lower altitudes?

The Earth's rotation causes the Coriolis effect, which deflects air masses to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This rotation creates wind patterns and influences the distribution of heat and moisture in the atmosphere, resulting in changes in atmospheric conditions at different altitudes.

5. What role does human activity play in the rapid changes of the atmosphere at lower altitudes?

Human activities, such as burning fossil fuels and deforestation, release large amounts of greenhouse gases into the atmosphere. These gases trap heat and contribute to the warming of the Earth's surface, causing changes in temperature and other atmospheric conditions at lower altitudes. Human activity also affects air quality and can lead to changes in the composition of the atmosphere.

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