Satellite Measurements of Solar Spectral Irradiance

Satellite Measurements of Solar Spectral Irradiance LASP University of Colorado tom.woods@lasp.colorado.edu March 2006 1

Talk Outline Motivation for Solar Spectral Irradiance solar energy input climate changes atmospheric absorption chemistry changes Summary of Satellite Measurements previous and current measurements Variations of Solar Spectral Irradiance Solar Cycle composite time series to study long-term variations Solar Rotation IR variability is more than expected Flares variations are as large as solar cycle variations flare total energy is more than expected March 2006 2

Solar Spectral Irradiance (SSI) Spectral irradiance is the solar radiance integrated over the solar disk Sometimes called the full-disk radiation Energy units of W / m 2 / nm TSI = SSI 0 Often normalized to a distance of 1.0 AU TSI = Total Solar Irradiance dλ Range Min - Max (nm) Hard X-ray 0.001-0.1 XUV 0.1-10 EUV 10-120 FUV 120-200 MUV 200-300 NUV 300-400 Visible 400-760 NIR 760-1400 MIR 1400-3000 FIR 3000 nm - 1 mm ISO #21348 Definitions March 2006 3

Solar Variability at Different Wavelengths Various images of the sun from SOHO showing solar activity Full-disk images: B/W: visible light from MDI showing sunspots Red & Green: EUV images from EIT showing active regions and flares QuickTime and a YUV420 codec decompressor are needed to see this picture. Off-disk images: LASCO coronagraph showing streamers of particles and coronal mass ejections (CMEs) movie from SOHO web site March 2006 figures from J. Lean 4

The Earth's Radiation and Energy Balance Satellite measurements required to accurately measure the top of the atmosphere (TOA) solar irradiance Note this solar energy is averaged over Earth s surface E = I π R E 2 4 π R E 2 = 1 4 I E For I =1368 W m 2 E = 342 W m 2 March 2006 5

Absorption Has Wavelength Dependence Solar radiation drives heating, chemistry, and dynamics in the atmosphere. Atomic and molecular species dominate absorption in the ultraviolet Water (clouds) and aerosols dominate the absorption and scattering in the visible and near infrared from P. Pilewskie (Solar Physics, 2005) March 2006 6

Solar Forcing is Dependent on Solar Variability Climate effects are wavelength dependent through both where the solar radiation is absorbed and by how much the solar radiation varies. Model of Solar Variability Model results of Solanki and Unruh (1998) UARS and SORCE SOLSTICE channels provide the required accuracy for λ < 260 nm SORCE SIM provides the required accuracy for 200 < λ <2000 nm from Solanki & Unruh (A & A, 1998) March 2006 7

TSI Record Relies on Continuity Satellite measurements of TSI have been made since 1978. Current TSI measurements are from SOHO VIRGO, ACRIMSAT, and SORCE TIM. Glory from G. Kopp March 2006 8

Continuity Also Important for SSI Measurements Same issues for spectral time series in combining data sets Calibration differences Instrument degradation issues Factor of 2 difference is sometimes found in the UV range Example is composite Lyman-α (121.6 nm) time series from T. Woods (JGR, 2000) March 2006 9

SORCE Measures TSI and SSI Solar Radiation and Climate Experiment (SORCE) Instrument λ Range (nm) λ (n m) TIM: Total Irradiance Monitor TSI (all) - SIM: Spectral Irradiance Monitor 200-2700 1-30 SOLSTICE: Solar Stellar Irradiance Comparison Experiment 115-320 0.1 XPS: XUV Photometer System 0.1-27, 121.6 7-10 SORCE spacecraft was launched on 25 January 2003, and its mission is through 2008. Next SORCE workshop is 20-22 Sept 2006 in San Juan Islands, WA: Earth s Radiative Energy Budget http://lasp.colorado.edu/sorce/ March 2006 10

TIMED SEE Measures Solar VUV Irradiance TIMED spacecraft was launched on 7 December 2001, and its mission has been extended through 2010. XUV EUV FUV EGS 27-194 nm with λ=0.4 nm XPS 0.1-34 nm with λ=7-10 nm and Ly-α (121.6 nm) with λ=2 nm http://lasp.colorado.edu/see/ EGS = EUV Grating Spectrograph Rowland-circle grating spectrograph with 64x1024 CODACON (MCP-based) detector XPS = XUV Photometer System Set of 12 Si photodiodes - 8 for XUV, 1 for Ly-α, and 3 for window calibrations March 2006 11

Examples of Solar Variations Solar Cycle (11-years) Solar Rotation - days to months Beacon effect of active regions rotating with the Sun (27-days) Solar Cycle - months to years Evolution of solar dynamo with 22-year magnetic cycle, 11-year intensity (sunspot) cycle Long-term H I Lyman-α time series has been extended with TIMED SEE measurements XUV 0-7 nm H I 121.5 nm Solar Rotation (27-days) Flares - seconds to hours Related to solar storms (such as CMEs) due to the interaction of magnetic fields on Sun SORCE and TIMED SEE are providing new information on solar irradiance variability Flares March 2006 12

Solar Variability From Active Region Evolution Active region (sunspot) evolution is driven by the emergence of magnetic fields from within the solar convection zone few, if any, active regions during solar cycle minimum many active regions during solar cycle maximum 11-year sunspot cycle, but 22-year magnetic cycle (solar dynamo driven) SC MIN SC MAX 1991 MAX Yohkoh X-ray Images (from L. Acton) 1995 MIN SOHO EIT EUV Images QuickTime and a YUV420 codec decompressor are needed to see this picture. March 2006 13

New Results for Solar EUV Variability TIMED SEE provides new, more accurate results of the solar EUV variability since the AE measurements in 1970s (Woods et al., JGR, 2005). TIMED SEE, SORCE, and UARS used to develop new proxy models of the solar UV irradiance (0-200 nm). UARS = UARS SOLSTICE solar cycle results [Woods and Rottman, 2002] Example variability for the 4 components of the Flare Irradiance Spectral Model (FISM) by Phil Chamberlin (CU PhD dissertation, 2005). March 2006 14

New Results on Solar Visible & IR Variability SORCE SIM providing new, more accurate results of the solar variability in the 200-2000 nm range (Harder et al., Solar Phys., 2005). Understanding solar variability is being advanced with solar irradiance modeling that includes identifying different solar active features (sunspot, plage, active network, etc.). Example: Solar Radiation Physical Model (SRPM) uses PSPT solar images to identify 7 solar features (Fontenla et al., Ap J, 2005). semi-empirical solar models region of PSPT solar image March 2006 15

Surprises for Solar IR Variability IR sunspot contrast is more than expected, but less than TSI variations. Yet IR faculae contrast is more than TSI variations (time period A). Fontenla et al., Ap J, 2004 Figure from J. Harder March 2006 16

Extraordinary Solar Storms during Oct-Nov 2003 QuickTime and a YUV420 codec decompressor are needed to see this picture. March 2006 17

October to November 2003 in Six Wavelengths The variations during the X17 flare on 28 October 2003 are as large as solar cycle variations (Woods et al., GRL, 2004). Measurement Rotation Variability Flare Variability TIM TSI SIM Visible 480 nm SOLSTICE Mg II 280 nm SOLSTICE Ly-α 121.6 nm XPS XUV 0-7 nm GOES XRS X-ray 0.1-0.8 nm -0.34% 270 ppm -0.34% - +20% 11% +25% 20% x 4 x 80 x 20 x 600 March 2006 18

SORCE TIM Clearly Detects X17 Flare in TSI Time Series First detection of flare in TSI record (G. Kopp, 2003) Figures from G. Kopp March 2006 19

Flare Total Energy is Larger than Expected Flare total energy is 10 times more than previous estimates (e.g. Emslie et al., JGR, 2004). XPS 0-27 nm flare contribution to total energy is 25% - 85% (Woods et al., JGR, 2006) Flare total energy, as observed at Earth, is highly dependent on the flare location. * TSI XPS (0-27 nm) x WLF (Hudson, 2006) Figures from Woods et al., JGR, 2006. March 2006 20

Summary Recent results for solar irradiance variations IR variations are more than expected Flare variations are as large as solar cycle variations for the largest flares (X10 class or larger) Flare total energy is about 10 times more than expected Future efforts New reference spectra of SSI (broader λ range, more accurate) Composite time series for long-term solar variability Improved SSI modeling (understanding solar magnetic fields) Thanks to instrument scientists and operations, data processing, and data analysis staff at LASP, JHU-APL, and GSFC. Solar irradiance data are available from NOAA, GSFC, and LASP (LISIRD) March 2006 21

LASP Scientist Phil Chamberlin Frank Eparvier Juan Fontenla Jerry Harder Greg Kopp Bill McClintock Peter Pilewskie Mark Rast Erik Richard Marty Snow Tom Woods Instrument Lead Rocket EGS FISM (model) TIMED SEE EGS SDO EVE MEGS SORCE SIM SRPM (model) SORCE SIM NPOESS SIM SORCE TIM Glory TIM PI NPOESS TIM SORCE SOLSTICE NPOESS TSIS PI HAO PSPT SORCE SIM NPOESS SIM SORCE SOLSTICE TIMED SEE PI SORCE PI SDO EVE PI Recent Changes at LASP Gary Rottman retired in 2005 Added Space Technology Building Wing A (75% more space for labs and offices) Vanessa George LASP Solar Influence Group Support data web site lasp.colorado. edu/lisird/ March 2006 22

Solar Irradiance Satellite Programs at LASP University of Colorado at Boulder data web site lasp.colorado. edu/lisird/ tom.woods@lasp.colorado.edu Future Current Past Satellite Instrument Years Operating Wavelength Range Rockets 1950-2004 0-320 nm SME 1981-1989 115-320 nm UARS SOLSTICE 1991-2005 119-420 nm TIMED SEE EGS XPS SORCE TIM SIM SOLSTICE XPS SDO EVE 2008-2014 0-105 nm NPOESS TIM SIM 2001-2010 2003-2008 2013-2023 27-195 nm 0-27 nm TSI 200-2000 nm 115-320 nm 0-27 nm Glory TIM 2007-2013 TSI TSI 200-2000 nm March 2006 23