Understanding solar spectral variability: A six-year comparison between SIM observations and the SATIRE model

Transcription

1 Understanding solar spectral variability: A six-year comparison between SIM observations and the SATIRE model Will T. Ball Imperial College London Yvonne C. Unruh, Nadine Afram, Imperial College Natasha Krivova, Sami Solanki; MPS Jerry Harder; LASP Image: BBC SORCE Meeting, Keystone, CO, May 2010

2 Outline SATIRE Model Total Solar Irradiance Spectral Solar Irradiance UV ( nm) Visible ( nm) IR ( nm) Conclusions

3 SATIRE: Modeling Solar Irradiance

4 SATIRE: Modeling Solar Irradiance Magnetogram Continuum Image Line-of-Sight Magnetic Field Correction Limb-darkening Correction Step 1

5 SATIRE: Modeling Solar Irradiance Magnetogram Identify Facular Pixels Continuum Image Identify Umbral and Penumbral Pixels Step 2

6 SATIRE: Modeling Solar Irradiance Magnetogram Continuum Image Bin pixel type with limb-angle Step 3

7 SATIRE: Modeling Solar Irradiance Spectra is applied to each pixel dependent on limb angle (and flux level for faculae). Model has one free parameter (that sets a saturation level that sets a limit for the relationship between magnetogram flux and brightness of faculae). In this comparison, data have been extended upto 2009; previous versions used a different free parameter; new value scales with noise. Result is light curve (TSI or SSI). Step 4

8 Total Solar Irradiance: Comparisons

9 Total Solar Irradiance Lower plot axis enlarged by to extent of bar (for all light curves) Compare with SIM TIM SATIRE year comparison. - Free parameter varied to match SATIRE gradient with TIM. - Do not pick up flux in 2008/9 period as a result of low MDI resolution.

10 Total Solar Irradiance Compare with SIM TIM SATIRE

11 Integrated nm - SIM black, SATIRE blue for all plots Int-SIM ( nm) Int-SATIRE ( nm) TIM / SORCE - Smoothed results of upper plot. 2008/12 (min) 2004/04 Int-SIM Int-SATIRE SATIRE TIM Wm Integrated ( Int- ) regions over nm - Are spectral regions contributing correctly in the early period? Only a small difference after end of 2004.

12 Spectral Solar Irradiance: Comparisons

13 nm 2008/12 (min) 2004/04 SIM SATIRE 1996/05 (min) 1993/08 SUSIM Wm Wm Clearest difference is SIM UV change in irradiance of ~x6 SATIRE; Stability in UV is good. - Over similar decline of TSI in previous cycle, SUSIM records only 0.06 Wm -2 decline.

14 nm - SATIRE overestimates rotational short-term amplitude (result of 1D model & linear scaling of brightness with flux). 2008/12 (min) 2004/04 SIM SATIRE 1996/05 (min) 1993/08 SUSIM Wm Wm

15 nm 2008/12 (min) 2004/04 SIM SATIRE Wm Large positive increase in the early period. SATIRE does not reproduce this. - Large visible region change balances to some degree the change observed in the UV.

16 nm 2008/12 (min) 2004/04 SIM SATIRE Wm Success of SATIRE is the very well matched rotational variability (best shown in the visible).

17 nm SATIRE Total Wm -2 Solar Irradiance 2008/12 (min) 2004/04 - Repeated story of visible (no long-term change in SIM SATIRE here) - Good agreement with active period. Models are entirely untested; SIM is the first instrument ever to observe IR continuously - No rotational variability picked up in latter period by SATIRE (strong in SIM); - Poor fit at minimum as only low flux faculae exist and are not picked up in MDI. SIM picks up variation.

18 nm 2008/12 (min) 2004/04 SIM SATIRE 0.00 Total Wm -2 Solar Irradiance Period of very low or no sunspot activity; allows analysis of facular / network induced variability only to be considered.

19 Int-SIM Int-SATIRE TIM UV SATIRE magnitude matches SIM; picking up flux, but not all. - No IR SATIRE variability on this scale. - Break down into IR regions and compare with UV/Vis TSI ; ppm variation.

20 Int-SIM Int-SATIRE TIM - Zoom in on SATIRE bars represent new scale - See inversion in longer IR especially in first rotation; lack of flux detected hides this variability. Reason for inversion is that the facular contrast turns negative in SATIRE above 1300nm.

21 - Magneto-convective results (N. Afram, Imperial College London, in preparation) suggest low flux network regions are bright here, though higher flux regions are darker. SATIRE Facular (FAL-P) MuRAM network (Afram in prep.) So SIM: suggests quiet Sun faculae are bright in IR; active period dark they are dark. SATIRE does not current match SIM: MDI flux contribution by wavelength needs magneto-convective results; faculae are bright if field weak and model currently scales with flux incorrectly; note that the magneto-convective model is LTE.

22 Conclusions

23 Conclusions SATIRE TSI reproduction very good. fails during quiet period; need higher resolution SATIRE UV/IR facular contrast incorrect. need magneto-convection results to remove free parameter SATIRE/SIM rotational agreement. notably visible region and integrated No agreement on long-term trend. large discrepancies spectrally SATIRE and SIM do not agree on longer-term trends; SIM reversal and agreement with magnitude decline would support observed trends favourably