  Ultra-hot Jupiters are the hottest close-in exoplanets discovered so far, and
present a unique possibility to explore hot and cold chemistry on one object.
The tidally locked ultra-hot Jupiter HAT-P-7b has a day/night temperature
difference of ~ 2500K, confining cloud formation to the nightside and efficient
ionisation to the dayside. Both have distinct observational signatures. We
analyse plasma and magnetic processes in the atmosphere of the ultra-hot
Jupiter HAT-P-7b to investigate the formation of a thermal ionosphere and the
possibility of magnetically coupling the atmospheric gas as the base for an
extended exosphere. We show which ions and atoms may be used as spectral
tracers, and if and where conditions for lightning may occur within the clouds
of HAT-P-7b, evaluate characteristic plasma and magnetic coupling parameters,
and a LTE radiative transfer is solved for the ionised gas phase. The
ionisation throughout HAT-P-7b's atmosphere varies drastically between day- and
nightside. The dayside has high levels of thermal ionisation and long-range
electromagnetic interactions dominate over kinetic electron-neutral
interactions, suggesting a day-night difference in magnetic coupling. K+, Na+,
Li+, Ca+, and Al+ are more abundant than their atomic counterparts on the
dayside. The minimum magnetic flux density for electrons for magnetic coupling
is B<0.5G for all regions of HAT-P-7b's atmosphere. HAT-P-7b's dayside has an
asymmetric ionosphere that extends deep into the atmosphere, the nightside has
no thermally driven ionosphere. A corresponding asymmetry is imprinted in the
ion/neutral composition at the terminators. The ionosphere on HAT-P-7b may be
directly traced by the Ca+ H&K lines if the local temperature is > 5000K. The
whole atmosphere may couple to a global, large-scale magnetic field, and
lightning may occur on the nightside.
