breaking the sound barrier

[dans]

Does anyone know if there is a physical sensation that accompanies breaking the 'sound barrier'? How would a flying superheroine know if she was going faster than sound or not? If you are going faster than sound, you can't hear the noise you are leaving behind. I don't think that suddenly the airflow around you changes from rough to smooth (or vice versa). You can leave a vapor trail without breaking the sound barrier, and you can break the sound barrier without leaving a vapor trail. 

I suppose she could be carrying an air-speed indicator of some sort but it seems unlikely. 

[redsycorax]

Here, these could be helpful:
boomsupersonic.com/flyby/how-exactly-do-you-break-the-sound-barrier
en.wikipedia.org/wiki/Sound_barrier
en.wikipedia.org/wiki/Supersonic_speed
www.aaas.org/breaking-sound-barrier
www.nasa.gov/history/SP-4219/Chapter3.html
www.pbs.org/wgbh/nova/barrier

[dans]

Thank you. I had always assumed that there was some change in the flight characteristics of a plane when it broke the 'sound barrier', for example, all of a sudden a rough flight smoothed out, or the power required to sustain that speed suddenly became significantly less. Because, it is called a 'barrier' and things must be different on the other side of the barrier. But all the reading I did suggests that to the pilots and passengers of a plane, there is virtually no difference between going a few miles below the speed of sound and a few miles above it. The turbulence doesn't alter drastically, the power curve doesn't make an unusual bend, the noises inside the plane don't change.

Given all that, there is really no way for a superhero to know if she has just broken the sound barrier when flying, unless she is carrying a wind speed indicator or a GPS of some sort.