If no external lighting source for apparent brightness of Jovian cloud bands, might such lighting be from emission radiation of ionized plasma at a somewhat deeper layer? Might such emission radiation have some association with ionized gas (plasma) moving along so described magnetic field lines at a somewhat deeper layer? Is there any relationship of luminosity intensity to density of so-called magnetic field lines?
Might any variation of band luminosity be due to cloud band density, and perhaps composition, rather than variation in luminosity source?
In an informal sense, might one entertain an analogy of a luminous corona associated with mass injection and magnetic re-connect i.e. stressed magnetic field? And adapt such processes to deeper jovian layered plasma?
Might also there be no ice crystals in upper cloud layers; since if there were, then any alleged backlighting would seem to result in refraction observable effects.