Sonic boom is that when the aircraft breaks through the sound barrier, due to the compression of the air can not spread rapidly, it will gradually form a shock surface  The highly concentrated acoustic energy on the shock surface causes a loud sound, which makes people feel a short and extremely strong explosion  Sonic boom occur only when they break through the sound barrier, that is, flying at supersonic speeds  The sonic booms cloud is a conical cloud with the aircraft as the central axis and spreads uniformly from the front of the wing to all sides  It is mainly due to the fact that the velocity of the air flow is faster than the conduction speed of the air when breaking through the speed of sound, which can not effectively pull down the airflow, resulting in a decrease in density, a decrease in air pressure, and water vapor condensing into tiny water droplets, which looks like a cloud-like state to the naked eye
Sonic boom cloud often appear in transonic flights, but not only in transonic flights
Supersonic flight when sonic boom occurs