  Electric discharges were detected directly in the cloudy atmospheres of
Earth, Jupiter and Saturn, are debatable for Venus, and indirectly inferred for
Neptune and Uranus in our solar system. Sprites (and other types of transient
luminous events) have been detected only on Earth, and are theoretically
predicted for Jupiter, Saturn and Venus. Cloud formation is a common phenomenon
in ultra-cool atmospheres such as in Brown Dwarf and extrasolar planetary
atmospheres. Cloud particles can be expected to carry considerable charges
which may trigger discharge events via small-scale processes between individual
cloud particles (intra-cloud discharges) or large-scale processes between
clouds (inter-cloud discharges). We investigate electrostatic breakdown
characteristics, like critical field strengths and critical charge densities
per surface, to demonstrate under which conditions mineral clouds undergo
electric discharge events which may trigger or be responsible for sporadic
X-ray emission. We apply results from our kinetic dust cloud formation model
that is part of the Drift-Phoenix model atmosphere simulations. We present a
first investigation of the dependence of the breakdown conditions in Brown
Dwarf and giant gas exoplanets on the local gas-phase chemistry, the effective
temperature and primordial gas-phase metallicity. Our results suggest that
different intra-cloud discharge processes dominate at different heights inside
mineral clouds: local coronal (point discharges) and small-scale sparks at the
bottom region of the cloud where the gas density is high, and flow discharges
and large-scale sparks near, and maybe above, the cloud top. The comparison of
the thermal degree of ionisation and the number density of cloud particles
allows us to suggest the efficiency with which discharges will occur in
planetary atmospheres.
