What is the difference between a shock wave and an expansion wave?
An adiabatic expansion lowers temperature, an adiabatic compression raises temperature, analogous to the way a refrigerator and an air conditioner work. Or a bicycle pump, it gets quite hot while you're pumping air.

A shock wave compresses air - at supersonic speeds the object travels faster than the pressure information, and when the object arrives at a bit of air it compresses suddenly in a shock wave, with corresponding higher temperature.