Rank of a FLARE based on its X-ray energy output. Flares are classified by the order of magnitude of the peak burst inten- sity (I) measured at the earth in the 1 to 8 angstrom band as follows:

Class (in Watt/sq. Meter)

B    I < 10^-7

C    10^-7<= I  <= 10^-6

M   10^-6 <= I <= 10^-5

X    I >= 10^-5
ON-LINE GLOSSARY OF SOLAR-TERRESTRIAL TERMS of National Geophysics Data Center