Radio burst classification at Metsähovi 
 

Type       Description

S          Spike or simple burst, duration less than 1 min 
S1         Minor simple burst, duration longer than 1 min, flux less than 1 sfu 
S2         Simple burst, duration 1 - 10 min, flux 1 - 50 sfu 
S3         Starting as a simple burst but generally looking as a GRF 
C          Complex burst, flux less than 50 sfu 
SER        Series of bursts, flux less than 50 sfu 
GB         Great burst, flux greater than 50 sfu  
RF         Minor rise and fall, duration less than 10 min 
GRF        Gradual rise and fall, duration longer than 10 min 


Reference: 

S. Pohjolainen, E. Valtaoja, and S. Urpo:
Solar microwave burst classification and correlation with soft X-rays
Astron. Astrophys. 306, 973- (1996)