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.