Well, Woody, I'm not sure that Superman would make a fireball in any case, when he is either falling or flying very fast through the atmosphere. Meteorites create fireballs when they fall through the atmosphere because they heat up so much that they partly or completely vaporize. That is not something that would happen to Superman, since he is invulnerable... on the other hand, his cape should burn up every time he flies really fast.
You're referring to ablation - where heat is dissipated by pieces falling off, and oxidation - burning up (rocks don't actually burn all that well.) BUT, you see the air compressing and getting red-hot even around things like space capsules and shuttles returning to Earth that aren't ablating or oxidizing - that's what causes ionization and radio blackout.
As to the sonic booms - sonic booms are created by the creation of air pressure building up in front of an object moving so fast the air can't get out of the way fast enough, creating a shock wave. In theory, if there was a way to prevent or minimize the shock wave as an object approaches and exceeds the speed of sound, you could prevent the sonic boom.
We need a nerd icon.
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