Observations of the Sun at Ultraviolet Wavelengths: 1 to 400 nm
Gary Rottman, Laboratory for Atmospheric and Space Physics
4. Future Observing Programs
We now have a record of the variation of total solar irradiance, and
of the variation of its ultraviolet spectral component, over two
complete solar cycles. However these observations represent only a
snapshot of the long term behavior of the Sun, and it is essential
that such measurements be continued. This extended data base will
allow us to more fully understand the nature of the Sun and the
physically processes underlying its variability. However, the
spectral knowledge that we have of solar variability is limited to
wavelengths short of 300 nm. In the visible and near infrared we can
place upper limits on solar variability, limits set for the most part
by observations of total solar irradiance. Since TSI varies only on
the order of 0.1%, it is difficult to reconcile spectral changes much
different than this value. It is just as unlikely that the spectral
character of the variations is "white" and invariant in wavelength.
Theories and modeling of solar radiation speak to a structured solar
variation, and to address and constrain such theories will require
visible and near infrared observations. The reason that more is
presently known about the ultraviolet variability is not that the UV
measurements are better, but only that their solar variations are so
much larger. Past spectral observations have been up to the task of
measuring one to a few percent changes, but they not been able to
record long term changes at the fraction of a percent level. This is
the challenge for future observations, and techniques based on
super-sensitive electrical substitution radiometers (ESR's) will soon
be applied to these observations. The next generation of irradiance
instruments should provide the spectral details underlying the envelope
of the TSI.
References
Acton, L. W., 1996, in "Proceedings of the
9th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun,''
ed. R. Pallavicinni and A. Dupree, (Provo: Astron. Soc of Pacific)
Brekke, P., Rottman, G. J., Fontenla, J., & Judge, P. G. 1996,
ApJ, 468, 418.
Brueckner, G.E., Edlow, K. L.,
Floyd, L. E., Lean, J. L., & VanHoosier, M. E.
1993, JGR, 98, 10695.
Cebula, R. P., Hilsenrath, E., & Deland, M. T. 1994, in
"The Sun as a Variable Star,''
eds. J. M. Pap, C. Frölich, H. S. Hudson, and S. K. Solanki,
(Cambridge: Cambridge), p. 81.
Frölich, C., and the VIRGO team: 1996, "First Results from the
VIRGO Experiment, Transactions AGU, Spring Meeting.
Kyle, H.L., Hoyt, D. V., Hickey, J. R., Maschoff, R. H., & Vallette, G. J. 1993,
"Nimbus-7 Earth Radiation Budget Calibration History - Part 1: The
solar channels", NASA Reference Publication 1316.
Lee, R.B.,
Gibson, M. A., Wilson, R. S., & Thimas, S. 1995, JGR, 100, 1667.
Rottman, G. J., Woods, T. N., & Sparn, T. P. 1993, JGR, 98, 10667.
White, O. R.,
1977, The Solar output and its Variation (Boulder: Colorado)
Willson, R. C. 1994, in
"The Sun as a Variable Star,''
eds. J. M. Pap, C. Frölich, H. S. Hudson, and S. K. Solanki,
(Cambridge: Cambridge), p. 54.
Woods, T. N.,
Rottman, G. J., Roble, R. G., White, O. R., Solomon, S. C.,
Lawrence, G. M., Lean, J., & Tobiska, W. K. 1994, "TIMED Solar EUV
Experiment,'' SPIE Proceedings, 2266, 467.
Woods, T. N.,
Prinz, D. K., Rottman, G. J., London, J., Crane, P. C., Cebula, R. P.,
Hilsenrath, E. Brueckner, G. E., Andrews,M. D., White, O. R.,
VanHoosier, M. E., Floyd, L. E., Herring, L. C., Knapp, B. G.,
Pankratz, C. K., & Reiser, P. A., 1996, JGR, 101, 9541.
[First | Prev | Discussion]
[Contents]