Solar Spectral Irradiance Measurements by LASP Frank Eparvier University of Colorado Laboratory for Atmsopheric & Space Physics eparvier@lasp.colorado.edu

LASP’s Irradiance History Spectral Region Wavelength (nm) Missions Soft X-ray (XUV) 0.1 - 30 SNOE, SORCE, TIMED, SDO Extreme Ultraviolet (EUV) 30-115 TIMED, SDO Far Ultraviolet (FUV) 115-200 SME, UARS, TIMED, SORCE Middle Ultraviolet (MUV) 200-300 SME, UARS, SORCE Near Ultraviolet (NUV) 300-400 UARS, SORCE Visible (VIS) 400-750 SORCE Near Infrared (NIR) 750-2700 Total Solar Irradiance (TSI) all SORCE, Glory Green indicates missions in development

Irradiance Calibration Essentials Understand the Measurement Equation: Know all the parameters that go into the measurement to irradiance conversion and assess how to best quantify each Do a thorough error analysis and uncertainty budget Calibrate pre-flight: Use a standard radiometric EUV source Primary standards, such as NIST SURF-III source, are preferred (note: SURF beam flux known to <1% for EUV ranges) Track in-flight: Any instrument changes that will affect results E.g. detector flat fields, gain changes, temperature effects, background signals, FOV maps, alignment changes… Re-Calibrate in-flight: As close after launch as possible (changes since pre-flight calib.) On a regular basis thereafter in order to track absolute changes E.g. redundant channels, on-board sources, rocket underflights, stellar comparisons Validate: With measurements made with other (preferrably independent) instrumentation Comparisons with models

TIMED Mission Ionosphere Mesosphere Thermosphere Energetics Dynamics TIMED primary science goals are to understand : energy transfer into and out of the Mesosphere and Lower Thermosphere/Ionosphere (MLTI) region of the Earth's atmosphere, and basic structure (i.e., pressure, temperature, and winds) of the MLTI region. TIMED launched on Dec. 7, 2001 Normal operations began on Jan. 22, 2002, extended through 2010

Solar EUV Experiment (SEE) Objectives Study the solar radiation input to the mesosphere, lower thermosphere, and ionosphere (MLTI) Accurately determine the solar vacuum ultraviolet (VUV: below 200 nm) irradiance Study the impact of solar changes on Earth’s upper atmosphere utilizing atmospheric models Improve the understanding of solar VUV variability Identify and quantify the sources of solar VUV variability Develop better proxy models of the solar VUV irradiance

EGS = EUV Grating Spectrograph SEE Instrumentation XUV EUV FUV EGS 27-194 nm with Dl=0.4 nm XPS 0.1-34 nm with Dl=7-10 nm and Ly-a (121.6 nm) with Dl=2 nm TIMED spacecraft was launched on 7 December 2001, and its mission has been extended through 2010. 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-a, and 3 for window calibrations Cadence = 10-sec integrations for 3 minutes of every 96 minute orbit http://lasp.colorado.edu/see/

SEE EUV Grating Spectrograph (EGS) Normal Incidence, 1/4 m Rowland Circle Spectrograph 27-194 nm range Dl = 0.4 nm (0.167 nm/pixel) Redundant channel used weekly for tracking degradation EUV FUV Example EGS Measurement Lyman-a Filter Flat Field (Hg) Lamp Detector HVPS Optical Cube Solar Aspect Sensor (SAS) Slit Selector Vacuum Door 64 x 1024 CODACON Charge Amp

SEE XUV Photometer System XUV Photometer System (XPS) 8 XUV Si photodiodes 0.1-34 nm Dl ~ 7 nm 1 Lyman-a (121.6 nm) photometer 3 bare (Vis) Si photodiodes measure FS filter transmission 8 position filter wheel 1 clear aperture per diode 2 fused silica filters per diode 5 blank apertures per diode Example XPS Measurement Filter Wheel (inside purge cover) Photodiode Electronics Section Control

SEE XPS Bandpasses + Ly- channel = channels used exclusively since July 2002 filter wheel anomaly

SEE Rocket Underflights SEE satellite instruments are calibrated regularly with sounding rocket underflights of prototype SEE instruments (XPS and EGS). Rocket instruments calibrated at NIST-SURF pre and post flight, to transfer calibration to SEE instruments. SEE underflights: 08-Feb-2002 12-Aug-2003 15-Oct-2004 24-Oct-2006 (will fly XPS and rocket version of EVE)

Rocket XPS Bandpasses + Ly- channel + For Oct. 2006 rocket flight, Be filter channels added to reproduce GOES XRS bandpasses

Solar Radiation and Climate Experiment (SORCE) SORCE Mission Solar Radiation and Climate Experiment (SORCE) PI: Tom Woods (Gary Rottman retired in 2005) Co-I’s: Jerry Harder, George Lawrence, Bill McClintock, Greg Kopp, Erik Richard, Marty Snow, and a bunch of others SORCE was launched on 25 January 2003, and its mission is through 2008.

Solar Irradiance Modeling SORCE Objectives Make daily measurements of total solar irradiance (TSI) with an absolute accuracy of 0.01% and with a long-term relative accuracy of 0.001% per year. Make daily measurements of the solar ultraviolet irradiance, 120 to 300 nm, with a spectral resolution of 1 nm, with an absolute accuracy of 5%, and with a long-term relative accuracy of 0.5% per year. Make daily measurements of the solar irradiance between 300 and 2000 nm with a spectral resolution (Dl/l) of at least 1/30, with an absolute accuracy of 0.05%, and with a long-term relative accuracy of 0.01% per year. Improve our understanding of how and why the variability occurs at the Sun and how the variable irradiance affects our atmosphere and climate. To use this knowledge to estimate past and future solar behavior and climate response. Total Irradiance Monitor (TIM) SOLSTICE Spectral Irradiance Monitor (SIM) Solar Irradiance Modeling Atmospheric Modeling

SORCE Measures TSI and SSI Instrument  Range (nm) (nm) 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 http://lasp.colorado.edu/sorce/

SORCE Total Irradiance Monitor (TIM) Instrument Type: Cavity Bolometer Wavelength Range: All Wavelength Resolution: N/A Optics: None Detector: Conical Electrical Substitution Radiometer (ESR) Absolute Accuracy: 0.01% (100 ppm) Long-term Accuracy: 0.001% (10 ppm) Field of View: 4° cone Mass: 7 kg Orbit Average Power: 14 W Orbit Average Data Rate: 1.6 kbits/s Redundancy: 4 ESRs (2 pairs) Heritage: New design Pre-flight Cal. Std: NIST Volt and Ohm In-flight Cal.: Redundant channels, Shuttle underflight

SORCE SOLAR STellar Irradiance Comparison Experiment (SOLSTICE) Instrument Type: Grating Spectrometer Wavelength Range: 115 - 320 nm Wavelength Resolution: 0.1 -0.2 nm Optics: Mirrors, Grating, ND Filters Detector: Photomultiplier Tube (PMT) Absolute Accuracy: 5% Long-term Accuracy: 0.5% Field of View: 1.5° x 1.5° Mass: 36 kg (2 channels) Orbit Average Power: 33 W (2 channels) Orbit Average Data Rate: 0.8 kbits/s (2 ch) Redundancy: Dual channels, dual PMTs Heritage: UARS SOLSTICE Pre-flight Cal. Std: NIST SURF-III In-flight Cal.: Bright early-type stars, Redundant channels

SORCE Spectral Irradiance Monitor (SIM) Instrument Type: Prism Spectrometer Wavelength Range: 200 - 2,000 nm Wavelength Resolution: 0.5 - 34 nm Optics: Prism Detector: ESR, Si photodiodes, and InGeAs photodiodes Absolute Accuracy: 0.03% (300 ppm) Long-term Accuracy: 0.006% (60 ppm) Field of View: 1.5° x 1.5° Mass: 18 kg Orbit Average Power: 42 W Orbit Average Data Rate: 2.0 kbits/s Redundancy: Dual channels Heritage: New design Pre-flight Cal. Std: Trap diode-NIST ESR In-flight Cal.: Redundant channels, Prism transmission

SORCE XUV Photometer System (XPS) Instrument Type: Filter Photometer Wavelength Range: 1-35 nm Wavelength Resolution: 5-10 nm Optics: Thin film filters (deposited on Si diodes) Detector: 12 Si photodiodes: 8 XUV, Ly-a, 3 bare Absolute Accuracy: 20% Long-term Accuracy: 4% Field of View: 4° cone Mass: 3 kg Orbit Average Power: 9 W Orbit Average Data Rate: 0.3 kbits/s Redundancy: 3 redundant XUV diodes Heritage: TIMED SEE, SNOE, rocket XPS Pre-flight Cal. Std: NIST SURF-III Ref. Si Diode In-flight Cal.: Redundant channels

SORCE XPS Bandpasses + Ly- channel = channels used routinely since Dec 2005 filter wheel anomaly (other channels used once monthly)

SDO Misson http://sdo.gsfc.nasa.gov/ SDO is the First Space Weather Research Network Mission in the LWS Program SDO Mission Science Objectives The primary goal of the SDO mission is to understand, driving towards a predictive capability, the solar variations that influence life on Earth and humanity’s technological systems by determining: How the Sun’s magnetic field is generated and structured How this stored magnetic energy is converted and released into the heliosphere and geospace in the form of solar wind, energetic particles, and variations in the solar irradiance. SDO Science Investigations EUV Variability Experiment (EVE) PI: Tom Woods, University of Colorado Measures the solar extreme ultraviolet (EUV) spectral irradiance to understand variations on the timescales which influence Earth’s climate and near-Earth space Helioseismic and Magnetic Imager (HMI) PI: Phil Scherrer, Stanford University Images the Sun’s helioseismic, longitudinal and vector magnetic fields to understand the Sun’s interior and magnetic activity Atmospheric Imaging Assembly (AIA) PI: Alan Title, LMSAL Provides multiple simultaneous high-resolution images of the corona over a wide range of temperatures to determine magnetic structure and variability Mission Specs: August 2008 launch Inclined Geosynchronous Orbit Five-year mission baseline 3-axis stabilized spacecraft Continuous solar pointing Data transmission: continuous high rate data stream ~150 Mbps compressed data at Ka-Band Mission development and management at GSFC Project Scientist Dean Pesnell http://sdo.gsfc.nasa.gov/

The EUV Variability Experiment (EVE) Principal Investigator: Tom Woods (Univ. Colorado - LASP) Co-Investigators: Univ. Colorado - LASP: Frank Eparvier, Gary Rottman Univ. Southern Calif.: Darrell Judge, Andrew Jones Naval Research Lab: Judith Lean, John Mariksa, Harry Warren, Don McMullin MIT-LL: Greg Berthiaume Univ. Alaska - GI: Scott Bailey Collaborators: NOAA - SEC: Tim Fuller-Rowell, Rodney Viereck Utah State Univ.: Jan Sojka Space Environ. Tech.: Kent Tobiska EVE Science Goal: Specify and understand the highly variable solar extreme ultraviolet (EUV) electromagnetic radiation and its impacts on the geospace environment and the societal consequences EVE Science Objectives: Specify Irradiance: Specify the solar EUV irradiance and its variability on multiple time scales (seconds to years). Understand Variability: Advance current understanding of how and why the solar EUV spectral irradiance varies. Nowcast/Forecast: Improve the capability to predict (nowcast and forecast) the EUV spectral irradiance variability. Geospace Impacts: Understand the response of the geospace environment to variations in the solar EUV spectral irradiance and the impact on human endeavors. http://lasp.colorado.edu/eve/

EUV Variability Experiment (EVE) EVE purpose: To measure and model the solar EUV irradiance variations due to flares (seconds), solar rotation (days), and solar cycle (years) ESP MEGS B/P MEGS A SAM EOP EEB The Key Components of EVE EVE Optical Package (EOP) Multiple EUV Grating Spectrograph (MEGS) MEGS A + SAM (Solar Aspect Monitor) MEGS B + P (Photometer Channel) EUV Spectrophotometer (ESP) EVE Electrical Box (EEB) EVE processor CCD power converter/regulator ESP power converters EVE Metrics Power Average (28V) 43.9 watts Mass 54.2 kg Data Rate 2 Kbps (engineering) 7 Mbps (science) Wave Length Range 0.1 nm – 105 nm Dimensions (EVE Envelope) ~39”L x 24”W x14”H

How does EVE measure the EUV? Multiple EUV Grating Spectrograph (MEGS) At 0.1 nm resolution MEGS-A: 5-37 nm MEGS-B: 35-105 nm At 1 nm resolution MEGS-SAM: 0-7 nm At 10 nm resolution MEGS-Photometers: @ 122 nm Ly-a Proxy for other H I emissions at 80-102 nm and He I emissions at 45-58 nm EUV Spectrophotometer (ESP) At 4 nm resolution 17.5, 25.6, 30.4, 36 nm At 7 nm resolution 0-7 nm (zeroth order) In-flight calibrations from ESP and MEGS-P on daily basis and also annual calibration rocket flights Dl 0.1 1 4 7 10 nm

EVE Calibration Rocket(s) Like TIMED-SEE, SDO-EVE will have periodic sounding rocket underflights to transfer calibration from NIST-SURF to satellite instruments. 1st flight of EVE rocket instruments planned for 24-Oct-2006 After SDO launch plan L+2 months, L+8 months, then increasing times after that for a total of 5 rockets for the 5 year SDO mission. Rocket Payload: MEGS (A, B, P, and SAM) ESP XPS CLASSIC (Ly-a imager) AXIS (0-5 nm avalanch photodiode)

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

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). Example variability for the 4 components of the Flare Irradiance Spectral Model (FISM) by Phil Chamberlin (CU PhD dissertation, 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]

Flare Irradiance Spectral Model (FISM) Developed by Phil Chamberlin (defended PhD 2005) Based on lots of data: Daily Average Data Sets: 0.1-27 nm: SEE Level 3 (Combination of SEE and SORCE XPS) 27-119 nm: SEE Level 3 (2002-Present) 119-190 nm: UARS SOLSTICE (1992-1996) Flare Impulsive Phase Data Sets: 0-27 nm: SORCE XPS (2003-Present) 27-190 nm: SEE Level 1 Flare Gradual Phase Data Sets: 0-190 nm: SEE Level 3A FISM is an Empirical Model 0.1-190 nm, 1 nm bins, 60-second resolution Models solar irradiance variations due to solar cycle, solar rotation, as well as both the impulsive and gradual phases of solar flares Daily Proxies: MgII c/w, Ly, 30.5 nm, F10.7, 36.5 nm, and 0-4 nm. Flare Proxies: GOES 0.1-0.8 nm and the time derivative (Neupert Effect)

FISM Results FISM matches solar variability on timescales of: Solar Cycle Solar Rotation Solar Flare FISM will be greatly improved with EVE: More flares (currently only 35 used) Longer timescales for full spectrum and for proxies Higher spectral resolution (0.1 nm?)

LISIRD http://lasp.colorado.edu/lisird/

Potential Collaborations/Validations TIMED-SEE XPS and EGS: XPS overlaps: 0-10 nm EGS overlaps: 27-70 nm, Ly- TIMED mission extended through 2010 TIMED observes for 3 minutes out of every 96 minute orbit SORCE: SOLSTICE overlaps: Ly- and 200-220 nm SIM overlaps: 200-220 nm SORCE prime mission is through 2008 SORCE observes for about ~60 minutes out of every 90 minute orbit SDO-EVE: ESP overlaps: 0-10 nm MEGS overlaps: 0-20 nm, 17-70 nm, and Ly-, and SWAP bandpass SDO due to launch August 2008 for 5 year mission SDO-EVE will observe continuously from GEO Sounding rockets: flights of XPS and EVE rocket instruments planned in October 2006 and regularly after launch of SDO (2008). FISM: Model can be used to generate full spectrum from Chromospheric, Transition-Region, Coronal, and Hot Coronal proxies. Could be tuned to use LYRA bandpasses.