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Coronal shocks are important structures, but there are no direct observationsof them in solar and space physics. The strength of shocks plays a key role inshock-related phenomena, such as radio bursts and solar energetic particle(SEP) generation. This paper presents an improved method of calculating Alfvenspeed and shock strength near the Sun. This method is based on using as manyobservations as possible, rather than one-dimensional global models. Twoevents, a relatively slow CME on 2001 September 15 and a very fast CME on 2000June 15, are selected to illustrate the calculation process. The calculationresults suggest that the slow CME drove a strong shock, with Mach number of3.43 - 4.18, while the fast CME drove a relatively weak shock, with Mach numberof 1.90 - 3.21. This is consistent with the radio observations, which find astronger and longer decameter-hectometric (DH) type II radio burst during thefirst event, and a short DH type II radio burst during the second event. Inparticular, the alculation results explain the observational fact that the slowCME produced a major solar energetic particle (SEP) event, while the fast CMEdid not. Through a comparison of the two events, the importance of shockstrength in predicting SEP events is addressed.

Strength of Coronal Mass Ejection-Driven Shocks Near the Sun, and Its Importance in Predicting Solar Energetic Particle Events