EUVAC: A solar EUV Flux Model for aeronomic calculations

Abstract

This paper presents a new solar EUV flux model for aeronomic calculations (EUVAC), which is based on the measured F74113 solar EUV reference spectrum. The model provides fluxes in the 37 wavelength bins that are in widespread use. This paper also presents cross sections to be used with the EUVAC flux model to calculate photoionization rates. The flux scaling for solar activity is accomplished using a proxy based on the F10.7 index and its 81‐day average together with the measured solar flux variation from the EUVS instrument on the Atmosphere Explorer E satellite. This new model produces 50‐575 Å integrated EUV fluxes in good agreement with rocket observations. The solar cycle variation of the chromospheric fluxes agrees well with the measured variation of the Lyman α flux between 1982 and 1988. In addition, the theoretical photoelectron fluxes, calculated using the new EUV flux model, are in good agreement with the solar minimum photoelectron fluxes from the Atmosphere Explorer E satellite and also with the solar maximum photoelectron fluxes from the Dynamics Explorer satellite. Its relative simplicity coupled with its ability to reproduce the 50‐575 Å solar EUV flux as well as the measured photoelectron spectrum makes the model well suited for aeronomic applications. However, EUVAC is not designed to accurately predict the solar flux variability for numerous individual lines.

Anomalous variations of <I>Nm</I>F2 over the Argentine Islands: a statistical study

“…Using the photoionization cross-section for atomic oxygen compiled by Richards et al (1994) and the EUVAC solar flux model (Richards et al, 1994), we conclude that, during atomic oxygen photoionization, a part of oxygen ions, which is created in electronically excited states, is larger than that forming electronically unexcited O + ( 4 S) ions with the production rate, P EUV . These electronically excited oxygen ions are converted to N + 2 and O + 2 ions, and O + ( 4 S) ions in chemical reactions constituting a large daytime source, P ex , of O + ( 4 S) ions through chemical reactions (see, e.g., Pavlov and Pavlova, 2005).…”

Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO): Overview of Science Objectives, Instrument Design, Data Products, and Model Developments

“…For these other instrument bands, their normalized responsivity profiles are convolved with the MEGS spectrum so that the EVE equivalent bands can be more directly compared for calibration and validation purposes. Some additional bands may also be produced using the band definitions for the PROBA2/Large Yield Radiometer (LYRA) instrument (Hochedez et al, 2006), the EUVAC solar irradiance model (Richards, Fennelly, and Torr, 1994), JB2006 and JB2008 atmospheric models (Bowman et al, 2008a(Bowman et al, , 2008b, and TIM-GCM model solar input (Solomon and Qian, 2005).…”

Subauroral red arcs as a conjugate phenomenon: comparison of OV1-10 satellite data with numerical calculations

“…In the present model, the solar EUV¯uxes, U G k , are obtained from the EUVAC model (Richards et al, 1994) or EUV94X model (Tobiska, 1993(Tobiska, , 1994. The reactions of photoionization and the ionization due to photoelectrons of the neutral species, N 2 Y O 2 Y O, and He are included in the model.…”

“…(A3) and (A5) in Pavlov (1994) to calculate j and D j . The revised photoionization and photoabsorption cross sections are taken from Richards et al (1994); these authors did not publish the photoionization cross section for He, and for these we have used values from Torr and Torr (1982). The Chapman function approximation is taken from Smith and Smith (1972).…”

“…The solar EUV¯uxes are obtained from the EUVAC model (Richards et al, 1994) or EUV94X model (Tobiska, 1993(Tobiska, , 1994. To specify the neutral temperature and the number densities of N 2 Y O 2 , O, and N we utilize the MSIS-86 model (Hedin, 1987) using the 3-h e p index as an indicator of the geomagnetic activity.…”