A well understood, but not necessarily true theory is that a atmospheric MASER (Laser, but with Microwave-Wavelenght-Spectrum*) of a volume in the order of km³ is building up somehow and pumps enough molecules (for the term pumping, please take lasers as reference again). Normaly this pumping energy should dissipate immediately. But with the atmospheric maser a solitary wave could emerge, which means that the wave is maintaining its shape locally while traveling at constant velocity (this part I don't really understand myself, but take the statement as reference for smarter boys to investigate) and can therefore keep a lot of molecules pumped in the same spot for quite a long time.
The beautiful thing about this theory, is that most men built structures can be fully penetrated by microwaves. This explains how ball lightning could happen spontaniously in closed rooms as it was reported before. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/93JD01021
(tl;dr, but most certainly helpful)
t. physicist from a very very different field
*"But Ernst, a Laser has just one well defined wavelenght", No. What about Ar/Kr-Lasers? They are white.