Solar Ultraviolet Irradiance Variations over Four Solar Cycles

Transcription

1 Solar Ultraviolet Irradiance Variations over Four Solar Cycles Tom Woods Laboratory for Atmospheric and Space Physics University of Colorado SSI Data Sets ( SME: G. Rottman UARS SOLSTICE: G. Rottman & T. Woods UARS SUSIM: L. Floyd TIMED SEE: T. Woods & F. Eparvier SORCE SOLSTICE: M. Snow & W. McClintock SORCE SIM: J. Harder & J. Fontenla Composite SSI (SBUV): M. DeLand SSI Models NRLSSI: J. Lean SATIRE: W. Ball SRPM: J. Fontenla W&R: T. Woods & G. Rottman

2 Aside on lower TSI Level LASP s TSI Radiometric Facility (TRF) has been key in providing new TSI instrument calibrations for Glory TIM, Picard PREMOS, SOHO PMOD, and ACRIM New result is lower TSI level of ~1361 W/m 2 Kopp & Lean (GRL, 2011)

3 Outline for Solar Spectral Variations Examples of solar cycle variability Composite H I Lyman-α (121.6 nm) Harder et al. (2009) SORCE SIM Result Solar cycle variability versus degradation Examining solar variability across solar cycle minimum (SCM) SME: SCM UARS: SCM SORCE and TIMED: SCM Composite solar cycle variability Comparison to SBUV observations Comparison to models NRLSSI, SRPM, SATIRE, W&R

4 Composite Solar UV Variability Example: H I Lyman-α by combining 5 different measurement sets and filling gaps with empirical models using proxies (e.g. F10.7) M. DeLand also has made composite solar UV ( nm) from 1978 to These composites can be downloaded from

5 Example solar cycle (SC) variability UV UV varies the most when variability is given as a ratio (percentage) However Variability given in energy units is more appropriate for climate studies Note that red lines are variations that are out of phase with the solar cycle. Solar Cycle (SC) variability from the NRLSSI model (J. Lean)

6 new SSI variability results from SORCE In addition to the infrared, some visible wavelengths are out of phase with the solar cycle Also, there is more UV variability than expected Are the SIM and model differences possibly related to unresolved instrument trends? Checking these results is challenging Other validation techniques are needed than direct comparisons Figures from J. Harder et al., GRL, 2009 Out of Phase Wavelengths

7 Comparison of Many Recent Studies Fig. 2 from TOSCA paper (Ermolli et al. 2012) TOSCA May 2012 Workshop : Recent variability of the solar spectral irradiance and its impact on climate modelling Harder et al Wavelength (nm) Next slides discuss this SORCE reanalysis which is really analysis of SC variability measurements from

8 Understanding degradation is critical for understanding solar variations Measurement = SIM uncorrected data at 280 nm

9 Technique: pick days of similar solar activity levels equal-distance from Min. SC Proxy composite: <TSI> <27 days> SSN (daily) <SSN> <Mg C/W> <Lyman-α> F10.7 <F10.7> Range: as each scaled to 100 for its SC variability range Reference Level is somewhat arbitrary Picked 2004/255

10 Assumption: average of variability before and after minimum = real solar variability Average Variability 1.5% (corrected) Versus Var. = Max/Min % 1.6% 1.9% (raw data) 8.0% -4.1% Technique Uncertainty is ~20%

11 This technique can be tested with missions that have measured over cycle minimum SC SME UARS SORCE ASIDE: Proxy composite has lower minimum in 2008, so variability for SC can be relatively larger for this technique (e.g. PMOD ΔTSI is x 2 larger) Proxy composite: <TSI> <27 days> SSN (daily) <SSN> <Mg C/W> <Lyman-α> F10.7 <F10.7> Range: as each scaled to 100 for its SC variability range Reference Level is somewhat arbitrary Picked 2004/255

12 PMOD TSI suggests same levels are reasonably selected. 3-σ variation for detrended 27-day smoothed TSI = 313 ppm

13 Solar Images for same levels

14 SSI data sets Fig. 3 in TOSCA paper (Ermolli et al. 2012) Solar Cycle (SC) 21/22 22/23 23/24 SC Composite (Woods SORCE reanalysis) includes SME UARS SOLSTICE & SUSIM TIMED SEE SORCE SOLSTICE & SIM

15 SME over solar cycle min Ideal Comparison Best Wavelengths nm

16 UARS SOLSTICE SC Min Best Wavelengths nm

17 UARS SUSIM SC Min Best Wavelengths nm

18 TIMED SEE SC Min Best Wavelengths nm

19 SORCE L3 SC Min SORCE L3 SOLSTICE: nm SIM: nm Best Wavelengths nm & nm

20 SORCE SIM L2 SC Min degradation trend fit to same levels first Best Wavelengths nm

21 Combine the best of each to make Composite Solar Cycle Variability Note that full solar cycle variation is about a factor of 3 more

22 Combine the best of each to make Composite Solar Cycle Variability Note that full solar cycle variation is about a factor of 3 more

23 ΔSSI / ΔTSI from this composite SSI 1-σ uncertainty is about ±30% Wavelength (nm) nm is 1.2% of ΔTSI nm is 28% nm is 116% So the nm range is most important for this comparison to TSI

24 DeLand SBUV-UARS SSI Comparison to this new Composite Measurement Best Wavelengths for SBUV nm

25 NRLSSI model (J. Lean) Comparison to Composite Measurement

26 SATIRE model (W. Ball) Comparison to Composite Measurement

27 SRPM model (J. Fontenla) Comparison to Composite Measurement

28 Woods & Rottman (2002) model Comparison to Composite Measurement

29 All Models compared to Composite nm

30 All Models compared to Composite nm

31 Conclusions Observations over a solar cycle minimum permit independent check on degradation trend (at ~20% of the variability) Solar ultraviolet variability observations and models agree best at wavelengths shorter than 210 nm No clear consistency found between observations or models for wavelengths longer than 260 nm Additional validation / analyses needed for the nm range of past missions. Additional (new) data sets are also needed.

32 Future SSI Measurements Can new instruments have little or no degradation for the UV-Vis-NIR? NOAA/NASA TSIS SIM 3 channels: daily, monthly, annual Improved lower-noise version of SORCE SIM Féry prism spectrometer covering the full wavelength range from the UV to IR using only one optical element for spectral dispersion and image quality

33 NUV-Vis-NIR Comparisons preliminary results

34 SORCE L3 SC minimum technique result ΔTSI 0.032%

35 SORCE SIM L2 degradation trend fit to same levels first ΔTSI 0.032%

36 All Models compared to Composite nm ΔSSI / ΔTSI nm 96% 130% 104% N/A 84% ΔTSI 0.032% Note that SIM nm SSI / TSI = 88% (expected for values above)

37 Backup Slides

38 List of days of same level Solar Cycle Minimum 1986/ / /280