Solar and Terrestrial Radio Disturbances

In their description of the solar radio emissions from the great sunspot of February 1946, Appleton and Hey1 pointed out that a number of sudden enhancements of intensity, observed at about 5 metres wave-length, occurred simultaneously with increases in D-layer ionization as indicated by fade-outs on long-distance radio-communication circuits. This increased ionization, which is believed to be due to enhanced solar ultra-violet radiations, strongly absorbs the radio communication waves (of the order of 20 metres wave-length) but does not produce any marked absorption of the solar radio emissions at wave-lengths of 5 metres or less.