Figure 4. Correlation between ratio of peak fluxes of flare microwave bursts at 17 and 35 GHz (parameter S₁₇/S₃₅) and spectral index of solar proton fluxes (parameter δ= lg(J₁₀/J₁₀₀). The rest is as in Fig. 1. The following events are marked by numbers: 16 - 12.06.1990, 30 - 20.02.1994, 31 - 20.10.1995, 49 - 02.04.2001, 59 - 26.12.2001, 60 - 20.02.2002, 75 - 11.04.2004, 81 - 20.01.2005.