Maintaining the Solar UV
Database in the 21st Century
DeLand1,
Future Solar UV Measurements
•Start with reference irradiance spectrum, calculate new
spectrum for different level of solar activity using
relationship(s) with proxy indexes.
Matthew T.
Richard P.
2
Linton E. Floyd , Thomas N. Woods3
1Science
Cebula1,
•Use of sunspot-darkening term provides information
for modeling near-UV (~300-400 nm) variations (e.g.
Lean et al. [1997]). Characterization can also be done
using Mg II index only [Krivova et al., in preparation].
Systems and Applications, Inc. (SSAI)
2Interferometrics
Synthetic Spectra
Inc.
3Laboratory for Atmospheric and Space Physics (LASP),
University of Colorado
•Linear scaling between Mg II and mid-UV irradiance
(~180-300 nm) has been demonstrated (e.g. DeLand and
Cebula [1993]).
•Combination of short-term and long-term contrast
factors can be derived for far-UV (~120-180 nm) (e.g.
Woods et al. [2000]).
Current Solar UV Measurements
•Nominal SORCE mission runs through 2008 (5 years). Request
for extension planned. No constraints on extended mission.
•Three SBUV/2 instruments are active, one more scheduled for
launch in 2008. Anticipate lifetime beyond 2010 based on
requirements for ozone data. No onboard calibration for
sensitivity changes.
•Flare Irradiance Spectral Model (FISM) models
vacuum UV (0-190 nm) with 1-minute cadence using
GOES X-ray data [Chamberlin, 2005].
•Semi-empirical model of near-UV and visible uses
PSPT Ca II K images to identify features that cause
irradiance variations (e.g. Fontenla et al. [1999]).
Lean et al. [1997]
•SOLSPEC (180-3000 nm), SOLACES (17-220 nm): Nominal
launch date in spring 2008 for 18-24 month deployment on
International Space Station (ISS). Experiments will be
recalibrated on Earth after mission.
•Total Solar Irradiance Sensor (TSIS) package will fly TIM and
SIM instruments on NPOESS environmental satellites.
Currently scheduled for C2 satellite with launch in ~2013.
•UARS operations ended August 2005. SUSIM V22 irradiance data
recently released. SOLSTICE V19 irradiance data are in preparation.
•EUVS sensor on GOES satellites will measure spectral band at
Lyman alpha (121.6 nm).
•Initial SORCE SOLSTICE and SIM data products available on-line.
•SORCE SOLSTICE and SBUV/2 Mg II index values are provided
operationally by NOAA SEC for use in Air Force space weather models.
Current Irradiance Data Sets
Continuation of Solar UV Data
•Overlap between SORCE and TSIS: Best option because of
similarity between instruments, complete onboard calibration.
However, NPOESS schedule issues make this difficult unless
SORCE is extended by ~5 years.
•SBUV/2 instrument(s) as link between SORCE and TSIS:
Need method to establish SBUV/2 sensitivity changes.
Response changes at 340 nm can also be tracked using Earth
view measurements of bright scenes. Evaluate spectral changes
by comparing dates with similar solar activity.
DeLand and Cebula [1993]
Woods et al. [2000]
Conclusions
•Solar spectral UV irradiance data now cover > 27 years from multiple individual instruments.
Merged irradiance data set will be created for general use.
•Quality and consistency of data have steadily improved.
•Current measurements from SORCE SIM represent heritage data for NPOESS TSIS instruments.
•If SORCE and TSIS measurements do not overlap, spectral irradiance models based on current
measurements will be critical for estimating solar UV irradiance values.
References
Chamberlin, P. C. (2005), The Flare Spectral Irradiance Model, Ph.D. dissertation, University of Colorado, Boulder.
DeLand, M. T., and R. P. Cebula (1993), Composite Mg II solar activity index for solar cycles 21 and 22, J. Geophys. Res., 98, 12,80912,823.
•Absolute calibration agreement between instruments has improved
over time.
•Basic solar cycle behavior is consistently observed.
•Wavelength-dependent and time-dependent differences between data
sets still remain. Creation of merged irradiance data set is in progress.
Fontenla, J., O. R. White, P. A. Fox, E. H. Avrett, and R. L. Kurucz (1999), Calculation of solar irradiances. I. Synthesis of the solar
spectrum, Astrophys. J., 518, 480-499.
Lean, J. L., G. J. Rottman, H. L. Kyle, T. N. Woods, J. R. Hickey, and L. C. Puga (1997), Detection and parameterization of variations in
solar mid- and near-ultraviolet radiation (200-400 nm), J. Geophys. Res. 102, 29,939-29,956.
Woods, T. N., W. K. Tobiska, G. J. Rottman, and J. R. Worden (2000), Improved solar Lyman α irradiance modeling from 1947 through
1999 based on UARS observations, J. Geophys. Res., 105, 27,195-27215.
This work was supported by NASA Grant NNH05CC17C.