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6 Answers

Why is pressure higher on a cold day, but pressure decreases with temperature as you climb?

Asked by: 2213 views , , ,
Weather

I understand that on a cold day, the air is denser, and higher density = higher pressure.

I also understand that air pressure decreases with altitude because as you climb the weight of the air above you decreases. The lower pressure causes a decrease in both temperature and density.

Can someone help me wrap my brain around why in the first case cold temp = high density, but in the second case cold temp = low density?

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6 Answers



  1. Boston Air on Jun 20, 2020

    Great question.

    As you stated, as air cools its density increases. Dense air will have higher pressure.

    As we climb in an airplane, two things happen:

    1. The temperature decreases as we move away from the relatively warm surface of the Earth.

    2. The atmospheric pressure decreases due to less volume of air above us.

    Looking at situation 1 above can lead one to think that as they climb, air density and pressure should increase (due entirely to decreasing air temperature).

    However, the overall effect of situation 2 is more powerful. The decreasing atmospheric pressure due to increases in altitude “cancels out” the temperature effect on air pressure.

    This is why, as we climb higher, pressure decreases even though the temperature is also decreasing.

    The decreasing volume of air above you has a greater effect than temperature when it comes to overall changes in atmospheric pressure in a climb.

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  2. cmpt7 on Jun 20, 2020

    @Boston Air

    Does the temperature only decrease due to the distance from the warm surface of the earth? Or is it also a result of the decrease in pressure?

    Because I thought low pressure = low temperature, and vice versa.

    Which is confusing because if it air cools it becomes more dense, which means higher pressure, which means…it warms up again?

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  3. Boston Air on Jun 20, 2020

    I’m no meteorologist, but… the heat from the sun warming the Earth’s surface is the primary driver of all weather. The Sun’s rays heat the surface through radiation and that energy is then transferred into the atmosphere by convection. This is primary reason the temperature decreases with altitude in the troposphere. Pressure change also plays a role, but it’s secondary to the effect of the Sun at the low altitudes where most flight training takes place.

    I hope that clears things up!

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  4. HelixPtera on Jun 30, 2020

    The Pressure and Temperature both decrease with altitude because the volume of the sphere is increasing. Stated differently: As altitude increases, Density decreases. We experience density through Temperature and Pressure.

    Given: Pressure = Perpendicular force per unit Area, and Temperature = Average Kinetic Energy per unit Volume, as we move up the air column we find fewer and fewer molecules of gas exerting a Perpendicular force as well as fewer molecules present, thus reducing the amount of total (and therefore average) amount of kinetic energy per volume.

    Your question happens to have the answer already stated in it, albeit a little confusing. Pressure decreases with altitude but not BEAUSE of temperature decrease, it’s because there is a reduction in total Density. Density is the ratio of Mass/Volume, and since mass is decreasing as we go up (fewer molecules jammed together due to gravity compressing the atmosphere) and volume is increasing (because each layer of the Sphere has a larger volume than the layer below it).

    We aren’t graphing Pressure Vs. Temperature, we are graphing both of them vs Density. Does that make sense?

    Pressure/Temperature = mass of the gas/Volume, therefore P/T = Density

    Pressures and Temperatures are just another way of looking at Density. See also calculating Density and Pressure altitudes.

    More in-depth explanation will feature the ideal gas law:

    PV = nRT

    as well as an understanding of Adiabatic processes. [https://en.wikipedia.org/wiki/Adiabatic_process]

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  5. tory on Mar 02, 2021

    can anyone prove to me pressure is higher on a cold day ? wind speed: zero

    a column of air from surface to top of atmosphere weighs the same regardless of its temp or density.

    with warm temps, the atmosphere is taller or expanded upward, not outward; with colder temps the atmosphere has shrunk or compressed.

    keep in mind, altimeter measures your distance from the top of atmosphere, where the weight of the air column is zero, to your altitude.

    if you walk a hundred miles at the surface at the coastline, your atmospheric pressure never change. before you start walking set altimeter to 29.92 (and assume temp is 80* F); after a hundred miles assume temp has dropped to 60*F; your altimeter, set at 29.92, will read zero altitude (no change in altitude or pressure).

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  6. cmpt7 on Mar 08, 2021

    @Tory

    My understanding is that as the column of air cools and contracts, more air fills in above the column, increasing the total mass. Plus cold air is often drier, which makes it heavier. I’ve also been taught that a cold air mass can exert more force on the surface due to its sinking/downward motion.

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