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We input solar wind parameters responsible for the main phases of 15 greatgeomagnetic storms (GGSs: $\Delta$SYM-H$\le-$200 nT) into the empiricalformulae created by \cite{Burton1975}(hereafter Burton equation), and by\cite{OBrien2000}(hereafter OM equation) to evaluate whether \textbf{twoequations} can correctly estimate the intensities of GGSs. The results showthat the intensities of most GGSs estimated by OM equation are much smallerthan the observed intensities. The RMS error between the intensities estimatedby OM equation and the observed intensities is \textbf{203} nT, implying thatthe estimated storm intensity deviates significantly from the observed one. TheRMS error between the intensities estimated by Burton equation and the observedintensities is 130.8 nT. The relative error caused by Burton equation for thestorms with intensities $\Delta$SYM-H$<$-400 nT is larger than 27\%, implyingthat the absolute error will be large for the storms with $\Delta$SYM-H$<$-400nT. The results indicate that the two equations cannot work effectively in theestimation of GGSs. On the contrary, the intensity of a GGS estimated by theempirical formula created by \cite{WangCB2003} can always be very close to theobserved one if we select the right weight for solar wind dynamic pressure,proving that solar wind dynamic pressure is an important factor for GGSintensity, but it is overlooked in the ring current injection terms of Burtonequation or OM equation. This is the reason why the two equations cannot workeffectively in the estimation of GGSs.

Can we estimate the intensities of great geomagnetic storms($\Delta$SYM-H$\le -$200 nT) by Burton equation or by O'Brien and McPherron equation?