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We report X-ray spectroscopic results for four giant solar flares occurred on2005 September 7 (X17.0), 2005 September 8 (X5.4), 2005 September 9 (X6.2), and2006 December 5 (X9.0), obtained from Earth albedo data with the X-ray imagingspectrometer (XIS) onboard Suzaku. The good energy resolution of the XIS(FWHM$\sim$100 eV) enables us to separate a number of line-like features anddetect the underlying continuum emission. These features include Si He$\alpha$,Si Ly$\alpha$, S He$\alpha$, S Ly$\alpha$, Ar He$\alpha$, and Ca He$\alpha$originating from solar flares as well as fluorescent Ar K$\alpha$ and ArK$\beta$ from the Earth atmosphere. Absolute elemental abundances (X/H)averaged over the four flares are obtained to be $\sim$2.0 (Ca), $\sim$0.7(Si), $\sim$0.3 (S), and $\sim$0.9 (Ar) at around flare peaks. This abundancepattern is similar to those of active stars' coronae showing inverse firstionization potential (i-FIP) effects, i.e., elemental abundances decrease withdecreasing FIP with a turnover at the low end of FIP. The abundances are almostconstant during the flares, with an exception of Si which increases by a factorof $\sim$2 in the decay phase. The evolution of the Si abundance is consistentwith a picture that the i-FIP plasma originates from the chromosphereevaporation and then mixes with the surrounding low-FIP biased materials.Flare-to-flare abundance varied by a factor of 2, agreeing with pastobservations of solar flares. Finally, we emphasize that Earth albedo dataacquired by X-ray astronomy satellites like Suzaku and XRISM can significantlycontribute to studies of solar physics.

Inverse FIP Effects in Giant Solar Flares Found from Earth X-Ray Albedo with Suzaku/XIS