NRLEUV 2: A new model of solar EUV irradiance variability

Abstract

NRLEUV represents an independent approach to modeling the Sun’s EUV irradiance and its variability. Instead of relying on existing irradiance observations, our model utilizes differential emission measure distributions derived from spatially and spectrally resolved solar observations, full-disk solar images, and a database of atomic physics parameters to calculate the solar EUV irradiance. Recent updates to the model include the calculation of a new quiet Sun differential emission measure distribution using data from the CDS and SUMER spectrometers on SOHO and the use of a more extensive database of atomic physics parameters. Here, we present comparisons between the NRLEUV quiet Sun reference spectrum and solar minimum irradiance observations. Although there are many areas of agreement between the modeled spectrum and the observations, there are some major disagreements. The computed spectra cannot reproduce the observed irradiances at wavelengths below about 160 Å. The observed irradiances appear to overstate the magnitude of the EUV continua. We also present some initial comparisons between the NRLEUV irradiance variability model and TIMED/SEE data. We find that the NRLEUV model tends to overpredict the absolute magnitude of the irradiance at many wavelengths. The model also appears to underpredict the magnitude of the solar-cycle and solar rotational variation in transition region emission lines.