People in the field have gone back and forth on this, but you might like this paper, which is the best piece of evidence I've seen for it in a specific case of

People in the field have gone back and forth on this, but you might like this paper, which is the best piece of evidence I've seen for it in a specific case of a specific flash. Look in particular at Figure 6 to see the lightning breakdown starting just at the ionization front (curved surface) of the cosmic ray shower: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JD032273 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/201...