CHAPTER 2. ATMOSPHERIC PRESSURE
Gas Pressure; Atmospheric Pressure – Pressure Profile; Hydrostatic Pressure Thus, the atmospheric pressure always decreases with height. . combined in the single relationship known as the ideal gas law or the equation of state: Some application of the gas law is involved in most practical problems in meteorology. Elevation above sea level - in feet and meter - with barometric and atmospheric = normal temperature and pressure at sea level (Pa) Related Topics. Here T is the absolute temperature, R is the universal gas constant equal to ρ= MPRT. Putting this into the differential relation for dP gives: . Solved Problems.
How to calculate altitude from current temperature and pressure? - Physics Stack Exchange
If water were used instead of mercury, the height of the column equivalent to normal pressure would be The Gas Laws The example of the gas-filled balloon can also be used to explore the basic gas laws see also Appendix D, p.
In the following, lets assume that the balloon is tight, so that the amount or mass of air in it stays the same: With density being the ratio of mass per volume, the gas density of the balloon thus varies only with its volume when mass is held constant.
If we squeeze the balloon, we compress the air and two things will happen: Since density is mass over volume, and the mass stays constant, the rise in density means that the volume of the balloon decreases: For two states of pressure P1, P2 and two corresponding volumes V1, V2this is stated mathematically: This in turn increases the rate at which the gas molecules bombard the skin of the balloon. Cooling the balloon down again will make the balloon shrink.Variation of Atmospheric Pressure with Altitude (GA_M-FLD21)
For two states with temperatures T1, T2 and two corresponding volumes V1, V2: One might then expect different components to have different scale heights determined by their molecular weight. In particular, considering the difference in molecular weight between N2 and O2, one might expect the O2 mixing ratio to decrease with altitude.
However, gravitational separation of the air mixture takes place by molecular diffusion, which is considerably slower than turbulent vertical mixing of air for altitudes below km problem 4. Turbulent mixing thus maintains a homogeneous lower atmosphere.
Pressure and the Gas Laws
Only above km does significant gravitational separation of gases begin to take place, with lighter gases being enriched at higher altitudes. During the debate over the harmful effects of chlorofluorocarbons CFCs on stratospheric ozone, some not-so-reputable scientists claimed that CFCs could not possibly reach the stratosphere because of their high molecular weights and hence low scale heights.
In reality, turbulent mixing of air ensures that CFC mixing ratios in air entering the stratosphere are essentially the same as those in surface air. Exercise The cruising altitudes of subsonic and supersonic aircraft are 12 km and 20 km respectively. What is the relative difference in air density between these two altitudes? The air density at 20 km is only a third of that at 12 km.
The high speed of supersonic aircraft is made possible by the reduced air resistance at 20 km.