A quick baro-pressure question

[UnAnswerd]

Why is it, that as air temperature increases, barometric pressure also increases? I would tend to think that the increased temperature would reduce air density, thus causing the air to weigh less, and ultimately lower the barometric pressure.

 

[paulsalem]

I have Boyles!

Boyles law

For a closed environment (not our atmoshpere) as pressure increases temperature also increases. And volume will decrease. (n is the universal gas constant (i think))

However this doesn't really happen in our atmospehre b/c is isn't a closed sytem.

PV=nRT

 

[pilotman2105]

PV=nRT

R is the universal gas constant (as a fixed value). n is the number of moles of gas.

In a given system, where volume and moles are constant, an increase in temperature increases pressure. The hotter something gets, the quicker the individual molecules of gas move. The faster they move, the more pressure they exert when they "bounce" off the side of the said container.

 

[UnAnswerd]

R is the universal gas constant (as a fixed value). n is the number of moles of gas.

In a given system, where volume and moles are constant, an increase in temperature increases pressure. The hotter something gets, the quicker the individual molecules of gas move. The faster they move, the more pressure they exert when they "bounce" off the side of the said container.

Okay, so the Earth's atmosphere is "sealed", in terms of air molecules being unable to transition into space?

 

[paulsalem]

No air molecules can escape into space, however the amout of air molelues at 100,000 feet are very few. As in a few per cubic mile.

However, I'm not the person to talk about weather patterns and causes. I'm not very strong in it, I'll differ to someone else.

But I wouldn't think the atmosphere is a closed container.

 

[CesnaCaptn]

Landed in Lincoln, NE today. Temp was 0 degrees F and press. was 30.85. Never seen that before.

 

[paulsalem]

30.71 and just above 0F. Tansponder said -001 for pressure alt.

 

[pilotman2105]

I'm going to break this down with your original post. It will be easier.

Why is it, that as air temperature increases, barometric pressure also increases?

The atmosphere is not "sealed" as mentioned before. The only thing keeping our atmosphere here is gravity. No gravity, no atmosphere. Before, I was simply providing a hypothetical situation to illustrate the formula PV=nRT.

I would tend to think that the increased temperature would reduce air density

Correct. Hence an increase in density altitude with higher temperatures. As the pressure drops, or temperature increases, the density altitude will increase.

thus causing the air to weigh less

The "weight" of air is determined by the number of air molecules, which changes with pressure. How far apart they are spread is a function of temperature. Hotter they are, the further apart they are.

and ultimately lower the barometric pressure.

In my mind, temperature and pressure are independent of each other until you need to calculate density altitude. Whether or not it's a flawed way to think of it, I don't know, but it's kept me straight thus far.

Boyle's law, as was described earlier, is for a closed system (anything that is completely sealed, like a balloon). The earth isn't that ideal, thus Boyle's law doesn't quite work.

Hopefully that helps.