The theory, previously published, of plane waves in an ionized medium pervaded by static electric and magnetic fields is shown to predict wave amplification, and consequent electromagnetic noise, in certain frequency bands. It is then developed in detail for the case in which the static fields are both parallel to the direction of wave propagation and the perturbations are transverse to this direction.

It is shown that for any given frequency and electron drift velocity there are two trios of such waves, $E_1$ and $E_2$ waves, all circularly polarized; the $E_1$ and $E_2$ waves are oppositely polarized. It is found that any transverse perturbation temporally prescribed at a given plane can be split up into two such trios which can then be considered independently.

Necessary and sufficient conditions are then found under which a growing flux of energy carried by $E_1$ or $E_2$ waves can pass normally through the boundary between two different ionized media.

The theory is applied to show that under simple hypotheses about the drift of electrons in the atmosphere above a large sunspot strong circular waves can arise by growth of random transverse perturbations and can then escape from the sun. The consequences of two such hypotheses are compared with known observations of solar noise and used to interpret them.

It is concluded that the general hypothesis that electrons in a sunspot have a drift motion leads to results which are in good agreement with many facts about strong solar noise and which do not disagree with any others.

The ultimate intensity which a growing perturbation can attain is also discussed.

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