W.K. Peterson 1 , J.M. Fontenla 1 , T.N. Woods 1 ,

1. Photoelectrons as a Tool to Evaluate Spectral and Temporal Variations of Solar EUV Irradiance Models W.K. Peterson1, J.M. Fontenla1, T.N. Woods1, P.G. Richards2, S.C. Solomon3, H.P. Warren4, W.K. Tobiska5, and P.C. Chamberlin6 1LASP/CU, 2George Mason, 3NCAR/HAO, 4NRL, 5Utah State, 6NASA/GSFC Peterson, MURI, October 2003

2. Outline • Our method to compare photoelectron energy observations and irradiance models • Comparisons of photoelectron energy spectra with those predicted with two photoelectron production codes driven by the SPRM predictive model, and the FISM, HEUVAC, S2000, and NRL irradiance models • Conclusions: • Surprisingly the empirical HEUVAC (EUVAC extended to 1 nm) model produces photoelectron spectra that match the observations on daily and solar rotation period time scales. • The SRPM prediction model matches the data as well or better than any of the data or index driven models. • The physics based NRLEUV model does the poorest job of capturing the variation of energetic photoelectrons on a solar rotation time scale. Peterson, MURI, October 2003

3. Uncertainties in solar Irradiances create uncertainties in thermospheric models Altitude-wavelength dependence of energy deposition from solar irradiance in units of Log10(Wm-4) From Solomon and Qian 2005 Solar minimum conditions Color Bar: Log10(Wm-4) Peterson, MURI, October 2003

4. Photoelectron Observations FAST observations available from January 1, 1997 to April 30, 2009 ePOP observations available in late 2011 Peterson, MURI, October 2003

5. Model Data Comparison Average of 56 one-minute average spectra obtained for SZA < 90o Two PE production codes Seven Solar irradiance models Peterson, MURI, October 2003

6. Transformation to Equivalent Wavelength Use a constant15 eV ionization potential Peterson, MURI, October 2003

7. Relative DifferenceObservation - Model / Modelas a Function of the Wavelength Equivalent of the Photoelectron Energy S/N inadequate below ~3 nm (> 385 eV) Above ~16 nm differences are less than +/- 50% Above ~30 nm slight differences in PE’s predicted from the GLOW and FLIP models. Both the GLOW and FLIP codes show TIMDED/SEE irradiances systematically low below about 15 nm * GLOW/HEUVAC best agrees with observations Peterson, MURI, October 2003

8. FAST Observations from August 31 to September 30 2005 Observed Photoelectron flux vs. Energy (eV) Vs. Equivalent Wavelength (nm) Each line in the color spectrogram panels shows a daily average photoelectron energy spectra with the flux given by the color bars on the right. F10.7 KP F10.7 AP DST Peterson, MURI, October 2003

9. Differences between Observations and Model PE Energy Spectra over a Solar Rotation Observation - Model / Model RED: Model >200% Low GREEN: Model = Obs BLACK: No data HEUVAC SPRM- Rome Photoelectron energy spectra produced using the empirical HEUVAC model agree best with Observations. The SPRM predictive model does as well as the TIMED/SEE based FISM model SPRM- MLSO FISM S2000 NRLEUV Peterson, MURI, October 2003

10. RED: Model >200% Low GREEN: Model = Observations BLACK: No data Observation-Model Differences -2 FISM produces good agreement except for underestimating the PE fluxes between 5 and 15 nm HEUVAC SPRM- Rome SPRM- MLSO S2000 produces low fluxes below 15 nm and relatively good agreement above 15 nm. FISM S2000 NRLEUV systematically underestimates the photoelectron flux below 15 nm NRLEUV Peterson, MURI, October 2003

11. Solar Irradiance Models Differ at Many Wavelengths HEUVAC Model Color Bar is Irradiance in w/m2 HEUVAC Relative Differences are (Model - HEUVAC) / HEUVAC SPRM- Rome SPRM- MLSO RED: Model >400% than HEUVAC Green: Model = HEUVAC Irradiance models are qualitatively different above and below ~27 nm FISM S2000 NRLEUV F10.7 Peterson, MURI, October 2003

12. HEUVAC SPRM-Rome Irradiance Power above and below 27 nm SPRM-MLSO FISM S2000 NRLEUV Lowest: NRLEUV Highest: HEUVAC/S2000 Lowest: HEUVAC/NRL Highest: SPRM Photoelectron spectra produced using HEUVAC agree best with data Peterson, MURI, October 2003

13. Irradiance Spectral Models • HEUVAC model has by design has broad spectral structure (~1eV) above 27 nm • To first order all models agree about the spectral shape below 27 nm • The most significant differences between irradiance models are in the relative power above and below 27 nm. HEUVAC SPRM-Rome SPRM-MLSO FISM S2000 NRLEUV Peterson, MURI, October 2003

14. Conclusions • Surprisingly the empirical HEUVAC (EUVAC extended to 1 nm) model produces photoelectron spectra that best match the observations on daily and solar rotation period time scales. • Fontenla’s SRPM prediction model matches the photoelectron data as well or better than any of the other data or index driven models investigated. • The physics based NRLEUV model does the poorest job of capturing the variation of energetic photoelectrons on a solar rotation time scale. • We need SDO/EVE observations to fully understand the temporal and spectral variations of solar irradiance. Peterson, COSPAR, 2010, C12-0018