Critical Mach Number has nothing (directly) to do with altitude.

Mach Number has everything to do Temperature,

At the airport in Nampa, the altitude is 2537 feet MSL (mean altititude above sea level). Nampa is located in a relatively flat valley area (the treasure valley) along with Boise and Caldwell and other small towns. The variation in altitude in these surrounding areas is not great, so for a casual estimate, a this altitude is a good estimate for most of the area if the figure is not critical.

yes. It is called EMP or electro magnetic pulse.

altitude bloemfontein

Green is a non example of altitude.