Solar Physics

, Volume 250, Issue 2, pp 235–267 | Cite as

XUV Photometer System (XPS): Improved Solar Irradiance Algorithm Using CHIANTI Spectral Models

  • Thomas N. Woods
  • Phillip C. Chamberlin
  • W. K. Peterson
  • R. R. Meier
  • Phil G. Richards
  • Douglas J. Strickland
  • Gang Lu
  • Liying Qian
  • Stanley C. Solomon
  • B. A. Iijima
  • A. J. Mannucci
  • B. T. Tsurutani
Open Access


Solar soft X-ray (XUV) radiation is highly variable on all time scales and strongly affects Earth’s ionosphere and upper atmosphere; consequently, the solar XUV irradiance is important for atmospheric studies and for space weather applications. Although there have been several recent measurements of the solar XUV irradiance, detailed understanding of the solar XUV irradiance, especially its variability during flares, has been hampered by the broad bands measured in the XUV range. In particular, the simple conversion of the XUV photometer signal into irradiance, in which a static solar spectrum is assumed, overestimates the flare variations by more than a factor of two as compared to the atmospheric response to the flares. To address this deficiency in the simple conversion, an improved algorithm using CHIANTI spectral models has been developed to process the XUV Photometer System (XPS) measurements with its broadband photometers. Model spectra representative of quiet Sun, active region, and flares are combined to match the signals from the XPS and produce spectra from 0.1 to 40 nm in 0.1-nm intervals for the XPS Level 4 data product. The two XPS instruments are aboard NASA’s Solar Radiation and Climate Experiment (SORCE) and Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) satellites. In addition, the XPS responsivities have been updated for the latest XPS data processing version. The new XPS results are consistent with daily variations from the previous simple conversion technique used for XPS and are also consistent with spectral measurements made at wavelengths longer than 27 nm. Most importantly, the XPS flare variations are reduced by factors of 2 – 4 at wavelengths shorter than 14 nm and are more consistent, for the first time, with atmospheric response to solar flares. Along with the details of the new XPS algorithm, several comparisons to dayglow and photoelectron measurements and model results are also presented to help verify the accuracy of the new XUV irradiance spectra.


  1. Ajello, J.M., Shemansky, D.E.: 1985, J. Geophys. Res. 90, 9845. CrossRefADSGoogle Scholar
  2. Aschwanden, M.J.: 2004, Physics of the Solar Corona, Springer, Berlin. Google Scholar
  3. Aschwanden, M.J.: 2007, Astrophys. J. 661, 1242. CrossRefADSGoogle Scholar
  4. Bailey, S.M., Woods, T.N., Barth, C.A., Solomon, S.C., Canfield, L.R., Korde, R.: 2000, J. Geophys. Res. 105, 27179. CrossRefADSGoogle Scholar
  5. Bailey, S.M., Woods, T.N., Barth, C.A., Solomon, S.C., Canfield, L.R., Korde, R.: 2001, J. Geophys. Res. 106, 15791. CrossRefADSGoogle Scholar
  6. Brekke, P., Rottman, G.J., Fontenla, J., Judge, P.G.: 1996, Astrophys. J. 468, 418. CrossRefADSGoogle Scholar
  7. Carlson, C.W., McFadden, J.P., Turin, P., Curtis, D.W., Magoncelli, A.: 2001, Space Sci. Rev. 98, 33. CrossRefADSGoogle Scholar
  8. Chamberlin, P.C., Woods, T.N., Eparvier, F.G.: 2007, Space Weather 5, S07005. CrossRefGoogle Scholar
  9. Chifor, C., Del Zanna, G., Mason, H.E., Sylwester, J., Sylwester, B., Phillips, K.J.H.: 2007, Astron. Astrophys. 462, 323. CrossRefADSGoogle Scholar
  10. Christensen, A.B., Paxton, L.J., Avery, S., Craven, J., Crowley, G., Humm, D.C., et al.: 2003, J. Geophys. Res. 108, 1451. CrossRefGoogle Scholar
  11. Conway, R.R.: 1988, Photoabsorption and Photoionization Cross Sections of O, O2 , and N2 for Photoelectron Production Calculations: A Compilation of Recent Laboratory Measurements NRL-MR-6155, Naval Res. Lab., Washington, D.C. Google Scholar
  12. Dere, K.P., Landi, E., Mason, H.E., Monsignori Fossi, B.C., Young, P.R.: 1997, Astron. Astrophys. Suppl. 125, 149. CrossRefADSGoogle Scholar
  13. Garcia, H.A.: 1994, Solar Phys. 154, 275. CrossRefADSGoogle Scholar
  14. Garcia, H.: 2000, Astrophys. J. Suppl. 127, 189. CrossRefADSGoogle Scholar
  15. Hinteregger, H.E., Fukui, K., Gilson, G.R.: 1981, Geophys. Res. Lett. 8, 1147. CrossRefADSGoogle Scholar
  16. Johnson, P.V., Malone, C.P., Kanik, I., Tran, K., Khakoo, M.A.: 2005, J. Geophys. Res. 110, A11311. CrossRefADSGoogle Scholar
  17. Judge, D.L., McMullin, D.R., Ogawa, H.S., Hovestadt, D., Klecker, B., Hilchenbach, M., et al.: 1998, Solar Phys. 177, 161. CrossRefADSGoogle Scholar
  18. Kintner, P.M., Ledvina, B.M., de Paula, E.R.: 2007, Space Weather 5, S09003. CrossRefGoogle Scholar
  19. Landi, E., Del Zanna, G., Young, P.R., Dere, K.P., Mason, H.E., Landini, M.: 2006, Astrophys. J. Suppl. 162, 261. CrossRefADSGoogle Scholar
  20. Lanzerotti, L.J.: 2001, In: Song, P., Singer, H.J., Siscoe, G.L. (eds.) Space Weather, AGU Monograph 125, AGU, Washington Google Scholar
  21. Lean, J.: 1987, J. Geophys. Res. 92, 839. CrossRefADSGoogle Scholar
  22. Lean, J.: 1991, Rev. Geophys. 29, 505. CrossRefADSGoogle Scholar
  23. Liedahl, D.A., Osterheld, A.L., Goldstein, W.H.: 1995, Astrophys. J. 438, L115. CrossRefADSGoogle Scholar
  24. Marcos, F.A., Wise, J.O., Kendra, M.J., Grossbard, N.J., Bowman, B.R.: 2005, Geophys. Res. Lett. 32, L04103. CrossRefGoogle Scholar
  25. Meier, R.R.: 1991, Space Sci. Rev. 58, 1. CrossRefADSGoogle Scholar
  26. Meier, R.R., Picone, J.M.: 1994, J. Geophys. Res. 99, 6307. CrossRefADSGoogle Scholar
  27. Meier, R.R., Warren, H.P., Nicholas, A.C., Bishop, J., Huba, J.D., Drob, D.P., et al.: 2002, Geophys. Res. Lett. 29, 99 – 1. CrossRefGoogle Scholar
  28. Mewe, R., Gronenschild, E.H.B.M.: 1981, Astron. Astrophys. Suppl. 45, 11. ADSGoogle Scholar
  29. Mewe, R., Gronenschild, E.H.B.M., van den Oord, G.H.J.: 1985, Astron. Astrophys. Suppl. 62, 197. ADSGoogle Scholar
  30. Mewe, R., Lemen, J.R., van den Oord, G.H.J.: 1986, Astron. Astrophys. 65, 511. ADSGoogle Scholar
  31. Neupert, W.M.: 1968, Astrophys. J. 153, L59. CrossRefADSGoogle Scholar
  32. Pap, J.M., Fröhlich, C., Hudson, H.S., Solanki, S.K. (eds.): 1994, The Sun as a Variable Star: Solar and Stellar Irradiance Variations, Cambridge University Press, Cambridge. Google Scholar
  33. Picone, J.M., Hedin, A.E., Drob, D.P., Aikin, A.C.: 2003, J. Geophys. Res. 107, 1468. CrossRefGoogle Scholar
  34. Qian, L., Roble, R.G., Solomon, S.C., Kane, T.J.: 2006, Geophys. Res. Lett. 33, L23705. CrossRefADSGoogle Scholar
  35. Richards, P.G.: 2002, J. Geophys. Res. 107, 10. Google Scholar
  36. Richards, P.G., Fennelly, J.A., Torr, D.G.: 1994, J. Geophys. Res. 99, 8981. CrossRefADSGoogle Scholar
  37. Richards, P.G., Woods, T.N., Peterson, W.K.: 2006, Adv. Space Res. 37, 315. CrossRefADSGoogle Scholar
  38. Richmond, A.D., Ridley, E.C., Roble, R.G.: 1992, Geophys. Res. Lett. 19, 601. CrossRefADSGoogle Scholar
  39. Roble, R.G., Ridley, E.C., Richmond, A.D., Dickinson, R.E.: 1988, Geophys. Res. Lett. 15, 1525. CrossRefGoogle Scholar
  40. Rodgers, E.M., Bailey, S.M., Warren, H.P., Woods, T.N., Eparvier, F.G.: 2006, J. Geophys. Res. 111, A10S13. CrossRefGoogle Scholar
  41. Rottman, G.J.: 1987, In: Foukal, P. (ed.) Solar Radiative Output Variation, Cambridge Research and Instrumentation, Boulder, 71. Google Scholar
  42. Rottman, G.: 2005, Solar Phys. 230, 7. CrossRefADSGoogle Scholar
  43. Smith, R.K., Brickhouse, N.S., Liedahl, D.A., Raymond, J.C.: 2001, Astrophys. J. 556, L91. CrossRefADSGoogle Scholar
  44. Solomon, S.C., Qian, L.: 2005, J. Geophys. Res. 110, A10306. CrossRefADSGoogle Scholar
  45. Stone, E.J., Zipf, E.C.: 1974, J. Chem. Phys. 60, 4237. CrossRefADSGoogle Scholar
  46. Strickland, D.J., Lean, J.L., Daniell Jr., R.E., Knight, H.K., Woo, W.K., Meier, R.R., et al.: 2007, J. Geophys. Res. 112, A06313. CrossRefGoogle Scholar
  47. Sutton, E.K., Forbes, J.M., Nerem, R.S., Woods, T.N.: 2006, Geophys. Res. Lett. 33, L22101. CrossRefADSGoogle Scholar
  48. Tobiska, W.K.: 1993, J. Geophys. Res. 98, 18879. CrossRefADSGoogle Scholar
  49. Tobiska, W.K., Woods, T.N., Eparvier, F.G., Viereck, R., Floyd, L., Bouwer, D., Rottman, G.J., White, O.R.: 2000, J. Atmos. Solar-Terr. Phys. 62, 1233. CrossRefADSGoogle Scholar
  50. Tsurutani, B.T., Judge, D.L., Guarnieri, F.L., Gangopadhyay, P., Jones, A.R., Nuttall, J., et al.: 2005, Geophys. Res. Lett. 32, L03S09. CrossRefGoogle Scholar
  51. Warren, H.P., Mariska, J.T., Lean, J.: 2001, J. Geophys. Res. 106, 15745. CrossRefADSGoogle Scholar
  52. Wienhold, F.G., Anders, J., Galuska, B., Klocke, U., Knothe, M., Riedel, W.J., Schmidtke, G., Singler, R., Ulmer, U., Wolf, H.: 2000, Phys. Chem. Earth 25, 473. Google Scholar
  53. White, O.R. (ed.): 1977, The Solar Output and Its Variation, Colorado Assoc. Univ. Press, Boulder. Google Scholar
  54. Woods, T.N., Rottman, G.: 2005, Solar Phys. 230, 375. CrossRefADSGoogle Scholar
  55. Woods, T.N., Rottman, G., Vest, R.: 2005, Solar Phys. 230, 345. CrossRefADSGoogle Scholar
  56. Woods, T.N., Kopp, G., Chamberlin, P.C.: 2006, J. Geophys. Res. 111, A10S14. CrossRefGoogle Scholar
  57. Woods, T.N., Lean, J.L., Eparvier, F.G.: 2006, In: Gopalswamy, N., Bhattacharyya, A. (eds.) Proc. International Living With a Star Workshop, Quest Publications, Mumbai, 145. Google Scholar
  58. Woods, T., Rodgers, E., Bailey, S., Eparvier, F., Ucker, G.: 1999, In: Larar, A.M. (ed.) Optical Spectroscopic Techniques and Instrumentation for Atmospheric and Space Research III, Proc. SPIE 3756, 255. Google Scholar
  59. Woods, T.N., Tobiska, W.K., Rottman, G.J., Worden, J.R.: 2000, J. Geophys. Res. 105, 27195. CrossRefADSGoogle Scholar
  60. Woods, T.N., Bailey, S.M., Peterson, W.K., Warren, H.P., Solomon, S.C., Eparvier, F.G., Garcia, H., Carlson, C.W., McFadden, J.P.: 2003, Space Weather 1, 1001. CrossRefADSGoogle Scholar
  61. Woods, T.N., Acton, L.W., Bailey, S., Eparvier, F., Garcia, H., Judge, D., et al.: 2004a, In: Pap, J., Fox, P., Fröhlich, C., Hudson, H.S., Kuhn, J., McCormack, J., North, G., Sprig, W., Wu, S.T. (eds.) Solar Variability and Its Effect on Climate, Geophys. Monograph Series 141, AGU, Washington, 127. Google Scholar
  62. Woods, T.N., Eparvier, F.G., Fontenla, J., Harder, J., Kopp, G., McClintock, W.E., Rottman, G., Smiley, B., Snow, M.: 2004b, Geophys. Res. Lett. 31, L10802. CrossRefADSGoogle Scholar
  63. Woods, T.N., Eparvier, F.G., Bailey, S.M., Chamberlin, P.C., Lean, J., Rottman, G.J., Solomon, S.C., Tobiska, W.K., Woodraska, D.L.: 2005, J. Geophys. Res. 110, A01312. CrossRefGoogle Scholar
  64. Worden, J.R., White, O.R., Woods, T.N.: 1998, Astrophys. J. 496, 998. CrossRefADSGoogle Scholar
  65. Worden, J., Woods, T.N., Neupert, W.M., Delaboundiniere, J.P.: 1999, Astrophys. J. 511, 965. CrossRefADSGoogle Scholar

Copyright information

© The Author(s) 2008

Authors and Affiliations

  • Thomas N. Woods
    • 1
  • Phillip C. Chamberlin
    • 1
  • W. K. Peterson
    • 1
  • R. R. Meier
    • 2
  • Phil G. Richards
    • 2
  • Douglas J. Strickland
    • 3
  • Gang Lu
    • 4
  • Liying Qian
    • 4
  • Stanley C. Solomon
    • 4
  • B. A. Iijima
    • 5
  • A. J. Mannucci
    • 5
  • B. T. Tsurutani
    • 5
  1. 1.Laboratory for Atmospheric and Space PhysicsUniversity of ColoradoBoulderUSA
  2. 2.Physics and Astronomy DepartmentGeorge Mason UniversityFairfaxUSA
  3. 3.Computational Physics, Inc.SpringfieldUSA
  4. 4.High Altitude ObservatoryNational Center for Atmospheric ResearchBoulderUSA
  5. 5.Jet Propulsion LaboratoryPasadenaUSA

Personalised recommendations