Definition

A sudden outburst of ul­travio­let light on the sun, known as a Solar Flare, which produces abnormally high ionization in the region of the D-layer. The result is a sudden increase in radio wave absorption, with particular severity in the upper medium and lower high frequen­cies. It has negligible effects on the heights of the reflecting/­refracting layers and, consequently, upon critical frequencies, but enormous transmission may occur.