Variability of the solar soft X-ray irradiance (0.6–2.5 nm) with solar activity Original Research Article

The solar soft X-ray spectral irradiance between 0.6 and 2.5 nm varies by orders of magnitude between the “quiet Sun” and X-class solar flares, with the spectral distribution of emission changing markedly with increasing level of activity. Full-disk spectra recorded in this wavelength range with high spectral resolution (0.02 nm) and over a wide range of activity by scanning crystal spectrometers on early orbiting spacecrafts and sounding rockets provide detailed information on these changing spectral distributions. Photometric calibrations of available observations made on OSO3 and OSO5 have been updated using broad band soft X-ray ionization chamber measurements made concurrently with the spectrometer observations. In this paper, we present algorithms for both the integrated 0.8–2.0 nm flux and for specific spectral bands recorded by the scanning spectrometers in the 0.6–2.5 nm range. These results apply only to the Sun under non-flaring conditions. Results for flares will be presented in a subsequent paper.