What happens to the speed of electromagnetic (EM) energy traveling through air as the altitude increases?

The speed of electromagnetic (EM) energy traveling through air does increase with altitude. This phenomenon can be attributed to the reduction in air density and the decrease in the refractive index of air at higher altitudes.

At lower altitudes, the presence of more air molecules results in more scattering and absorption of EM waves, which can slightly slow down the transmission speed. As altitude increases, the air becomes less dense, allowing the EM waves to propagate with less interference. Consequently, the speed approaches the speed of light in a vacuum, which is faster than in denser mediums. Therefore, as altitude increases and air density decreases, the signal speed becomes faster, aligning with the principles of electromagnetic wave propagation in different mediums.