L-dwarf variability: Magnetic star spots or non-uniform clouds?

The recent discovery of photometric variations in L dwarfs has opened a discussion on the cause of the variations. We argue against the existence of magnetic spots in these atmospheres and favor the idea that non-uniform condensate coverage (i.e. clouds) is responsible for the variations. The magnetic Reynolds number (Rm) in the atmosphere of L dwarfs, which describes how well the gas couples with the magnetic field, is too small (<