0-9 | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
An abnormally high ionization density in the D region caused by an occasional sudden solar flare, i.e., outburst of ultraviolet light from the Sun. Note: The SID results in a sudden increase in radio-wave absorption that is most severe in the upper medium-frequency (MF) and lower high-frequency (HF) ranges. (188)