Weather Forecasting Advice: Understanding Atmospheric Density
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A correct understanding of density is fundamental in order to know how weather influences our lives. Density applies to all kinds of fluids, including gaseous atmospheres and apparent solids like glass, which in reality is indeed, a highly viscous liquid.
Density is related to mass (m) and volume (v) in the following way:
d=m/v
And it is a concept that expresses the amount of mass that it is contained in a given volume of fluid.
Thus, if we have a mass of air that is maintained as constant while it is being heated because no air is gained or loss during that process, but its volume will increase as pressure also increases, it is easy to see that hot air will always be less dense as while it is cold.
It is important to remember that as height increases pressure is reduced, but also, temperature becomes lower and lower until stratospheric heights are reached.
Then, our atmosphere suffers from two distinct tendencies: one, as density decreases due to lower pressures, and a contrary one, due to the fact that as atmospheric temperature decreases, so does its pressure.
In other words, thanks to these opposite processes, density does not decrease with height as rapidly as it should, taken as an isolated factor.
In theory, both tendencies could achieve a point of equilibrium; however, experimental evidence shows that density decreases with height even as temperature does the same.
On peaks such as K2 or Aconcagua, atmospheric pressure is about half of what we have at sea level, even considering that up there temperatures are remarkably low as well.
The final conclusion of all this is that pressure has more influence over density than temperature.
