  Hierarchical turbulent structure constituting a jet is considered to
reproduce energy-dependent variability in blazars, particularly, the
correlation between X- and gamma-ray light curves measured in the TeV blazar
Markarian 421. The scale-invariant filaments are featured by the ordered
magnetic fields that involve hydromagnetic fluctuations serving as electron
scatterers for diffusive shock acceleration, and the spatial size scales are
identified with the local maximum electron energies, which are reflected in the
synchrotron spectral energy distribution (SED) above the near-infrared/optical
break. The structural transition of filaments is found to be responsible for
the observed change of spectral hysteresis.
