been searching my memory for a matching pattern and i thought of electrical discharge(kind of) like lateral lightning arching along a horizontal path.
pockets of higher conductivity which ignites to the required flash over point requiring some of its own ignition energy.
like a fluid flowing from one hollow puddle to another, the surface tention requires a fraction more energy than the energy to maintain the burn/electrical charge.
you get a single ignition/conductivity and then a dissipating collapsing wave effect which has a reducing cyclic pattern.
im no good with math so some electrical engineer might make a better discription.
getting weird... it also looks the same as video conversion software as i mentioned above where you get false shadows appearing as the software seeks to fill out the gap.
exothermic electro-static discharge via an atmospheric ingition ?
Why do you have so much more believability then MR?
Not saying your explanation is correct but even if not correct its more correctored than a thousand MR ghost