What We've Learned from SORCE: Solar Cycle Maximum to Minimum! Overview of SORCE Mission! Expectations from SORCE! Solar Cycle Results from SORCE Tom Woods <tom.woods @ lasp.colorado.edu> LASP / University of Colorado J. Harder, G. Kopp, W. McClintock, J. Fontenla, P. Pilewskie, E. Richard, G. Rottman, M. Snow LASP / University of Colorado Solar Radiation and Climate Experiment SORCE Launch : January 25, 2003 SORCE Book Solar Physics Vol. 230, 2005 SORCE Solar Cycle Results - February 2008 1
SORCE Mission Overview Mission Status Irradiance Measurements Extended Mission Plans SORCE Solar Cycle Results - February 2008 2
SORCE: A Mission of Solar Irradiance for Climate Research " SORCE Measurements Total Solar Irradiance (TSI) Extend TSI record Improve upon accuracy and stability Solar Spectral Irradiance (SSI) 0.1-27 nm and 115-2400 nm Continue UV record for! < 400 nm Start new NUV-Vis-NIR record Daily cadence for data products SORCE TSI and SSI Data Products http://lasp.colorado.edu/sorce/ SORCE Solar Cycle Results - February 2008 3
Happy 5th Birthday SORCE! " SORCE Mission Launched January 25, 2003 5-year prime mission (thru Jan 08) Spacecraft and instruments are in excellent condition for extended mission Expect overlap with NASA Glory TIM (TSI only, no SSI measurements), ESA PICARD, and ESA SOLAR (on space station), but no clear future for NOAA TSIS SC Max SC Min SORCE Solar Cycle Results - February 2008 4
SORCE has TSI and SSI Instruments First time to simultaneously observe SSI from 0.1 nm to 2400 nm. Total Solar Irradiance (TSI) TIM Total Irradiance Monitor (TIM) FUV NUV-Visible-NIR SIM Spectral Irradiance Monitor (SIM) 200 2400 nm FUV EGS SOLSTICE TIMED SOLar STellar Irradiance Comparison Experiment (SOLSTICE) 115 320 nm X-ray XPS XUV Photometer System (XPS) 1 34 nm SORCE Solar Cycle Results - February 2008 5
SORCE Extended Mission Plans " SORCE received 4 more years from 2007 ES Senior Review Extended mission began Feb. 1, 2008 - operate until Jan. 2012 Will be part of 2009 ES Senior Review (every 2 years) " SORCE s overlap with future TSI and SSI measurements is critical to prevent a gap in the solar climate record ESA SOLAR on ISS: 2008-2011 Glory TIM (TSI only): 2009 launch ESA PICARD (TSI only): 2009 launch Need NASA/NOAA TSIS (TIM & SIM) to launch before 2014 " Focus on long-term variations Gérard Thuillier s talk (Tue AM) is about the ESA SOLAR instruments SORCE has observed solar cycle (SC) 23 declining phase and cycle minimum - will observe SC 24 rising phase during extended mission SORCE solar cycle results will help to improve reconstruction of the solar irradiance (TSI & SSI) back to the Maunder Minimum (1600s) SORCE Solar Cycle Results - February 2008 6
Expectations Before SORCE " Overlapping missions required for TSI climate record SORCE improves upon accuracy and stability for total solar irradiance (TSI) " Solar spectral irradiance (SSI) variability between 120 nm and 400 nm is well characterized SORCE extends the SSI wavelength coverage to shorter wavelengths and to longer wavelengths into the visible and near infrared (NIR) " Spectral contributions to the TSI variability is not accurately known SORCE new observations from 0.1 nm to 2400 nm will greatly improve knowledge on SSI variations SORCE Solar Cycle Results - February 2008 7
Total Solar Irradiance (TSI) - Before SORCE This level of accuracy requires overlapping measurements to study long-term trend of TSI SORCE Solar Cycle Results - February 2008 8
SORCE TIM Extends the TSI - Establishes Lower Value " Fundamental determination that the Total Solar Irradiance (TSI) is ~1361 W/m 2, not 1366 W/m 2 SORCE TIM has most accurate measurement (350 ppm vs. 1000 ppm) Validation effort with NIST is on-going; new TSI cal. facility at LASP Impacts Earth s radiation energy budget Greg Kopp s talk (Tue AM) will provide more details about SORCE TIM results SORCE TSI TIM -4.5 W/m 2 SORCE Solar Cycle Results - February 2008 9
TSI Trends - Conflicting Results Before SORCE " Fröhlich s PMOD composite shows little, if any, increase between solar minima in 1986 and 1996 Other data and analyses tend to support this result better " Willson s ACRIM composite shows large increase (0.05%) [Wilson & Mordvinov, GRL, 2003] 0.1% SC 0.05% LT [figure from Fröhlich & Lean, AAR, 2004] SORCE Solar Cycle Results - February 2008 10
TSI Recent Decline - Is Modern Maximum Over? " Downward trend of the TSI by 0.02% from last cycle minimum SOHO VIRGO (single instrument) has been measuring TSI since 1996 SORCE TIM agrees well with VIRGO trend since SORCE launch in 2003 ACRIM composite (multiple instruments) has same trend Lower TSI (if confirmed) implies a new natural cooling for climate change Steven Dewitte s and Claus Fröhlich s talks (Tue AM) will provide more details about long-term TSI results VIRGO Composite -0.02% ACRIM Composite -0.02% SORCE Solar Cycle Results - February 2008 11
Solar Spectral Irradiance (SSI) Poorly Known Before SORCE at! > 400 nm First time to have daily, full spectral coverage with the combination of SORCE and TIMED missions. VIS-NIR Hole (filled by SORCE) SBUV Measurements UARS, SBUV Estimates Models, Ground-based EUV Hole (filled by TIMED) (TSI) Solar Cycle (SC) variation estimate is from Fröhlich & Lean [AAR, 2004]. Note no variability assumed for! > 1600 nm SORCE Solar Cycle Results - February 2008 12
Surprise for Infrared Solar Cycle Variations " Infrared (IR) irradiance is out of phase with solar cycle New, unexpected result from SORCE SIM - still preliminary SIM IR channels have not shown any degradation, so don t suspect instrument effect But IR is in phase with the TSI for short-term variations (solar rotation) Chromospheric UV 240-280 nm Photospheric Visible H" 656 nm Agrees well with TSI Infrared (IR) 1500 nm Near H - opacity minimum See Jerry Harder and Erik Richard posters (Tue PM) for more details. SORCE Solar Cycle Results - February 2008 13
Solar Cycle Results from SORCE SORCE Solar Cycle Results - February 2008 14
Solar Variations Largely Driven by Magnetic Activity " What we know best: Day-to-day variations primarily from magnetic active regions Dark sunspots in visible Bright plage in UV Evolution of magnetic active regions drives solar cycle variations Competing dark sunspots and bright faculae for TSI and visible radiation Active network contribution is most important for transition region emissions Magnetic Field Visible (photosphere) Ultraviolet (chromosphere, transition region) SORCE Solar Cycle Results - February 2008 15
Wavelength Dependent Contributions to Solar Variability TSI 0.1% Ultraviolet 30% The primary sources of TSI variations are the dark sunspot and bright facular contributions. The primary sources of UV variations are the bright active region contributions. SORCE Solar Cycle Results - February 2008 16
Dark and Bright Contributions for! > 260 nm " Dark sunspots normally dominate photospheric emissions in the NUVvisible-NIR ranges Bright plage above the sunspots dominate the chromospheric (ultraviolet) emissions such as the Mg II emission (anti-correlation with 500 nm) " Bright faculae (active network) sometimes dominates If so, then photospheric and chromospheric variations are in phase This happens about once a year (during SORCE mission) Need at least 3 parameters to model solar irradiance: Active Region (sunspot, plage) Active Network (faculae) Quiet Sun (with LT trend) SORCE Solar Cycle Results - February 2008 17
Early Estimate of 11-year Solar Cycle Variation " In-phase variation in 2004 used as rough estimate of the 11-year solar cycle variation assumes active network is primary cause of solar cycle variation " Result suggests that the SC variation at! > 400 nm could be described by 2 K change in photospheric temperature UARS SC Ratio 0.01 = 1% SORCE Solar Cycle Results - February 2008 18
Estimated Solar Cycle Variability in Energy Units SORCE Solar Cycle Results - February 2008 19
Advances for Solar Irradiance Variations - 1 " Where improvements are needed: Spectral coverage needs to be expanded EUV:! < 120 nm Visible-NIR:! > 400 nm VIS-NIR Hole (filled by SORCE) SBUV EUV Hole (filled by TIMED) " SORCE and TIMED have provided new, simultaneous measurements to cover the full spectral range from 0.1 nm to 2400 nm SORCE Solar Cycle Results - February 2008 20
Advances for Solar Irradiance Variations - 2 " Where improvements are needed: Spectral coverage needs to be expanded EUV:! < 120 nm Visible-NIR:! > 400 nm Solar dynamo effects on long-term variations Conflicting predictions for next solar cycle maximum Maunder Minimum level Doug Biesecker s (Tue PM) and David Hathaway s (Wed PM) talks will provide details on predicting the next solar cycle. " NASA / NOAA predictions for next solar cycle are uncertain with +/- 40% variation from current cycle Dikpati and Gilman (Ap. J., 2006) predicts higher cycle Schatten (GRL, 2005) predicts lower cycle SORCE Solar Cycle Results - February 2008 21
Advances for Solar Irradiance Variations - 3 " Where improvements are needed: Spectral coverage needs to be expanded EUV:! < 120 nm Visible-NIR:! > 400 nm Solar dynamo effects on long-term variations Conflicting predictions for next solar cycle maximum Maunder Minimum level Eruptive events are not well understood Physical cause (prediction) Spectral variations " Flare variations can be larger than solar cycle variation " Total flare energy is about 10 times more than previous estimates Prior estimates: total is 10-15 times the GOES X-ray energy (0.1-0.8 nm) [e.g., Hudson & Willson, 1983; Hudson, 1991] TIM measurement: total is 150 times the GOES X-ray energy [Woods et al., JGR,2006] Flare energy (2-6 x 10 32 ergs) is comparable to CME energy (~10 32 ergs) SORCE Solar Cycle Results - February 2008 [Figure from Woods et al., GRL, 2003] 22
Solar Cycle Results: SORCE Mission Timeline " SORCE launched on Jan. 25, 2003 " Routine solar observations began in Mar. 2003 " SORCE has observed moderate activity for ~3 years and low activity for ~2 years Solar maximum was in early 2002 Solar minimum is perhaps Nov. 2007 Extended mission will observe next maximum 22 SC 23 24 SORCE Solar Cycle Results - February 2008 23
Solar Cycle Options During SORCE Mission " Smoothing helps to identify better time range for high activity Avoid out-of-phase UV-TSI periods Mid 2003 (or late 2004) 2003 time for high activity excludes SIM (quality of SIM data not improved until mid 2004) " Minimum of smoothed data is best for low activity (late 2007) High Activity Low Activity SORCE Solar Cycle Results - February 2008 24
Example for SORCE SOLSTICE and TIMED SEE " 2007/316 for Low Activity and 2003/192 for High Activity 27-day average used <F10.7> 81 is 70.5 and 131.4 So ~40% of full cycle activity TIM <TSI> 27 is 1360.545 and 1361.062 (0.038%) SIM s best data not available until mid 2004 " SORCE SOLSTICE: FUV values and variability are consistent with UARS results (ATLAS and VUV2002) " TIMED SEE: SEE improves EUV accuracy EUV variabilities are similar to AE-E (VUV2002) SC Variability EUV Ratio (accuracy) FUV SORCE Solar Cycle Results - February 2008 25
Infrared (IR) Variations are Particularly Interesting - 1 " IR is in phase with the TSI for short-term variations (solar rotation) Reduced variability in the IR relative to TSI variation Expected result due to H - opacity being low near 1600 nm TSI IR 1600 nm SORCE Solar Cycle Results - February 2008 26
Infrared (IR) Variations are Particularly Interesting - 2 " But IR irradiance is out of phase with solar cycle UV decreases towards solar minimum Visible very similar to TSI IR result is new, unexpected result from SORCE SIM still preliminary Juan Fontenla s talk (Wed PM) will discuss some physical possibilities for these infrared variations. (figure from Jerry Harder) SORCE Solar Cycle Results - February 2008 27
Examples for SORCE SIM " Although more active solar conditions in 2003, best SIM data are in 2004-2007 " Jerry Harder and Juan Fontenla examined solar images and selected several dates dominated by either sunspots, facula, or active network. " Following example uses the facula-reference example (with 27-day averages) Corresponds to <F10.7> of 72 and 91, so ~12% of full cycle activity (figure from Jerry Harder) See Jerry Harder s poster (Tue PM) for more details. SORCE Solar Cycle Results - February 2008 28
SIM Comparison to Other Reference Spectra " SIM has ~2% accuracy for! > 300 nm " SIM has offsets in 200-300 nm range Ratio (accuracy) " SIM has first daily spectral results for! > 400 nm " SIM and SOLSTICE are higher than UARS (VUV2002) and ATLAS results Additional validation SC Variability SORCE Solar Cycle Results - February 2008 29
Spectral Contributions to TSI Variability are Different " The facula example has much more UV contribution to the TSI variation, less in visible, and much less in the IR Some of the differences is due to solar variability from different time periods and some could be due to instrument degradation correction SORCE Solar Cycle Results - February 2008 30
Summary of Solar Cycle Results " Total Solar Irradiance (TSI) composites indicate a ~0.02% decline since the last minimum in 1996 Additional validation needed If so, then it is a cooling term for climate " Solar Spectral Irradiance (SSI) variations are newly being established for! > 400 nm Higher precision spectral variations in the ultraviolet (UV) confirm UARS results Spectral variations in the visible and near infrared (NIR) yield surprises " Improvements on the spectral contributions to the TSI About 1/3 to 1/2 from Visible About 1/4 to 2/3 from Near UV Additional validation for SIM trends VIRGO Composite IR 1600 nm TSI -0.02% SORCE Solar Cycle Results - February 2008 31