  In addition to X-rays, extreme ultraviolet (EUV) rays radiated from solar
flares can cause serious problems, such as communication failures and satellite
drag. Therefore, methods for forecasting EUV dynamic spectra during flares are
urgently required. Recently, however, owing to the lack of instruments, EUV
dynamic spectra have rarely been observed. Hence, we develop a new method that
converts the soft X-ray light curve observed during large flare events into an
EUV dynamic spectrum by using the Solar Dynamics Observatory / Atmospheric
Imaging Assembly images, a numerical simulation, and atomic database. The
simulation provides the solution for a coronal loop that is heated by a strong
flare, and the atomic database calculates its dynamic spectrum, including X-ray
and EUV irradiances. The coefficients needed for the conversion can be
calculated by comparing the observed soft X-ray light curve with that of the
simulation. We apply our new method to three flares that occurred in the active
region 12673 on September 06, 2017. The results show similarities to those of
the Flare Irradiance Spectral Model, and reconstruct some of the EUV peaks
observed by the EUV Variability Experiment onboard the Solar Dynamics
Observatory.
