For my book I talked with John Lewis, who wrote "Rain of Iron and Ice" and is an expert on such things. As I recall (the conversation was like 7 years ago now) direct collisions are what start things off, but as soon as a shock wave builds up you get a standoff shock a few meteroid radii in front (so if it's pea-sized, it's a few cm in front). The heat ionizes the air, and there was one particular chemical (I don't recall which one) that recombines and glows very brightly.
I think that meteor spectra show the presence of ionized air and ablated meteoroid material.
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