This is another question that is answered by current science, but answered very incompletely. We can see this by going to a physics forum, where we find a nearly perfect encapsulation of the current discussion.¹ Since this forum scores number 1 on a websearch, we may assume it is also fairly influential. It is both representative and well-placed. The first answer is by “chroot”, and it is that

Hot air is less dense and experiences a buoyant force, just like a bubble of air in water.

A member named “quartodeciman” answers,

Why doesn't the less dense hotter air simply diffuse into the denser cooler air across the given boundary layer? Why doesn't the system just slowly move to thermal uniformity without material exchange?

A member “krab” then expands the answer a bit:

By fluid mechanics, less dense objects float on top of denser objects, and so the hot air floats.

Quartodeciman then answers,

Why don't the cold air molecules just fall through the space between the hot air molecules and simply make a mix?

Member “franznietsche” then replies,

Simply, fluid dynamics doesn't work that way...why it doesn't...well...anyone?

Member “JohnDubYa” expands the answer once more:

The slower moving molecules will migrate downwards, because they do not have sufficient kinetic energy to maintain their elevation. On the other hand, the faster moving molecules will migrate upwards, because those that had sufficient kinetic energy to hit the top of the partition are now free to travel farther upward now that the partition has been removed. They stay towards the top because they are launched back upwards when elastically colliding with neighboring molecules.

You can see that no one has given a satisfactory explanation, though we have many variations of the standard model thinking on this. Quartodeciman seems to be the only one with a strong feeling that none of this is satisfactory. The others are pretty sure the answer is known, though they might or might not be able to express it fully.

Notice that JohnDubYa does not answer quartodeciman's questions. If we apply his answer to the atmosphere, his first sentence is not applicable. If the slower moving molecules don't have sufficient energy to maintain their elevation, why were they at that elevation to begin with? His answer can't apply to the hotter gas either, whether in a box or in the atmosphere, because the pressure of the gas is in all directions. Molecules will migrate both up and down and to every side. Heat is not preferential to the direction up any more than pressure is.

Chroot's answer is also false, from a first glance, as quartodeciman shows. A hotter gas should expand faster in all directions, increasing its volume. This will decrease its density, yes, but will not, without further theory, cause it to rise. Likewise, cold air of the same make-up will be denser. But according to the current theory of gravity, the field cannot recognize density. Denser things don't weigh more: things with more mass weigh more. Weight is a function of mass, not density; and rising or falling are caused by weight, not density. It should not matter how much cubic footage a gas covers, it should only matter how much it weighs. An expanding gas weighs the same when it is small as it does when it is large, so it should neither rise nor fall. This question can be answered only by ignoring very pertinent facts and the fundaments of gravitational theory. If we want to explain rising, we must have a mechanism, not just a statement of how things happen. We are not asking for a report, we are asking for a physical reason.

Member “Loren Booda” tells us,

According to statistical mechanics, where air has greater kinetic energy it has a greater probability to occupy a higher gravitational potential than less energetic air. That is, the system tends toward maximal entropy.

But that is another report. The statistics are based on observation, and explaining gravity with entropy is a dodge. We don't want an airy statistical mechanics, we want an old-fashioned mechanics that is capable of showing a physical mechanism.

Once again, this question cannot be answered with current theory, which is why the internet and textbooks are full of bad answers. We need the charge field of the Earth to answer it. The charge field is an emission field of real photons, and their (summed) direction is straight up from the surface of the Earth, radially out from the center. This explains rising heat very quickly and simply because we now have a way to bring density into the gravity equations, with simple mechanics. A gas that expands into greater volume will cover more area and encounter a larger section of the charge field. So it will encounter a larger force up, and will rise. It is that simple. An equal mass over a greater volume will rise because it is hit by more photons. This fact underlies all the partial explanations above, on the internet, and in textbooks.

Nor is this an electrical or magnetic answer, since the charge field can exist without any expression of electric or magnetic fields. If ions are present, the charge field will indeed induce electromagnetism, but the charge field is still there when no ions are present. Therefore it is no argument against me that the charge field has not been measured. No one has tried to measure it, independent of the electromagnetic field. Experimenters have so far assumed that measuring the electric or magnetic field is a measurement of the charge field, but it isn't. If the E/M field is present, then the charge field is, too. But lack of an E/M field is no proof of lack of a charge field. It is only proof of a lack of ions.

This simple mechanism also explains another mystery. It has never been understood how a gas maintains its energy, despite a colossal number of collisions. In a real gas, as opposed to an ideal gas, the collisions cannot be completely elastic. Energy must be lost over time to collision. But gasses have a way of maintaining energy, as if they had a constant source of propellant. They lose neither energy nor velocity, at least not to any extent we expect they would. Well, it turns out they do have a source of propellant, and that source is the charge field of the Earth. The charge field not only helps keep the atmosphere aloft, via simple bombardment, it also offsets most of the tendency of the gas to lose energy from collision. The charge field has a spin component as well as a linear component, and this keeps the gas moving in all directions.


¹http://www.physicsforums.com/archive/index.php/t-32331.html

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