  Extrasolar planets appear in a chemical diversity unseen in our own solar
system. Despite their atmospheres being cold, continuous and transient plasma
processes do affect these atmosphere where clouds form with great efficiency.
Clouds can be very dynamic due to winds for example in highly irradiated
planets like HD 189733b, and lightning may emerge. Lightning, and discharge
events in general, leave spectral fingerprints, for example due to the
formation of HCN. During the interaction, lightning or other flash--ionisation
events also change the electromagnetic field of a coherent, high energy
emission which results a characteristic damping of the initial, unperturbed
(e.g. cyclotron emission) radiation beam. We summarise this as 'recipe for
observers'. External ionisation by X-ray or UV e.g. from within the
interstellar medium or from a white dwarf companion will introduce additional
ionisation leading to the formation of a chromosphere. Signatures of plasma
processes therefore allow for an alternative way to study atmospheres of
extrasolar planets and brown dwarfs.
