Solar Ultraviolet Spectral Irradiance:
Early Results From the SOLar STellar Irradiance
Comparison Experiment II Aboard the SORCE Spacecraft
William E. McClintock, Martin Snow, Gary J. Rottman, and Thomas
N. Woods
LASP/University of Colorado
William.mcclintock@colorado.edu
Bill McClintock
SORCE Science Meeting
December 4 2003
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SOLSTICE: Science Objectives and Measurements
Science Objectives:
•Measure solar irradiance from 115 to 320 nm with 0.5 nm spectral
resolution and 5% or better accuracy
•Monitor solar irradiance variation with 0.5% accuracy during the
SORCE mission
•Establish the ratio of solar irradiance to the average flux from an
ensemble of bright early-type stars with 0.5% accuracy for future
studies of long-term solar variability.
Measurements:
•Wavelength Coverage: 115 - 320 nm
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•Solar Spectral Resolution: 0.1 nm
•Stellar Spectral Resolution : 1.1 - 2.2 nm
Bill McClintock
SORCE Science Meeting
December 4 2003
2
SOLSTICE: Experiment Concept
Solar Observation: Modified Monk-Gillieson Spectrometer
Solar Exit Slit
Photomultiplier Detector
Diffraction
Grating
Camera Mirror
Entrance Slit
Stellar Observation: Objective Grating Spectrometer
Stellar Exit Slit
Camera Mirror
Photomultiplier Detector
Diffraction
Grating
Entrance Aperture
•The optical configuration matches illumination areas on the detector
•Interchanging entrance slits and exit slits provides ~ 2x105 dynamic range
•Different stellar/solar integration times provide ~ 103 dynamic range
•A optical attenuator (a pair of neutral density filters), which can be
measured in flight, provides additional ~ 102 dynamic range in the MUV
wavelength range for λ>220 nm
Bill McClintock
SORCE Science Meeting
December 4 2003
3
SOLSTICE: Past and Present
SORCE SOLSTICE has direct heritage
to the very successful UARS SOLSTICE
Three separate wavelength channels
G: 115-180 nm, CsI Photocathode
F: 160-320 nm, CsTe Photocathode
N: 280-430 nm, Bialkali Photocathode
Sunshade
Solar/Stellar
Entrance Slit
Mechanism
Grating
Fold Mirrors
Off Axis Ellipse
Photomultiplier
Detector
Solar/Stellar
Entrance Slit
Mechanism
Bill McClintock
SORCE Science Meeting
December 4 2003
4
SOLSTICE: Present and Future
•
Two identical instrument channels meet the SORCE
Mission lifetime requirement:
-Channel A primary wavelength range: 170-320 nm
-Channel B primary wavelength range: 115-180 nm
•
Each channel covers both wavelength ranges for
redundancy and cross calibration.
Bill McClintock
SORCE Science Meeting
December 4 2003
•
Solar and stellar irradiance are measured with the
same optical-detector chain
•
Accurate pre-flight calibration using the NASA beam
line at the NIST Synchrotron Ultraviolet Radiation
Facility (SURF III)
•
Precise measurements of solar and stellar irradiance of
bright, early-type stars that, according to stellar theory,
vary by <1% in 104 years
•
Stellar measurements provide:
- Accurate in-flight instrument calibration tracking
- The basis for comparing SOLSTICE solar
irradiance measurements with future work
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SOLSTICE: What’s Inside
Bill McClintock
SORCE Science Meeting
December 4 2003
6
SOLSTICE: Observing Modes
•
Science
– Normal Scans (10 per day)
• ~40 minute duration
• High Signal-to-Noise
– Quick Scans
• ~8 minute duration
• Fill in around other activities
– Mini Scans
• 64 steps covering HI and SiIII near 121 nm
• 128 steps covering MgI and MgII near 280
• One orbit per day and fill in around other activities
– Stellar Observations
•
Calibration and Degradation
– Stellar Observations
• Nighttime each orbit
• Zero order scan followed by a series of fixed wavelengths followed by zero order scan
–
–
–
–
Fixed wavelength‘T’ scans map FOV and track ‘burn-in’ , done weekly
Full scan FOV maps track ‘burn-in’ done quarterly
A/B comparison experiments done weekly
Filter transmission measurements done daily
Bill McClintock
SORCE Science Meeting
December 4 2003
7
SOLSTICE: Typical Irradiance Spectra
SORCE SOLSTICE has ~ 0.1 nm spectral
resolution across its entire wavelength range
SORCE SOLSTICE Solar Spectrum
1013
SORCE SOLSTICE Solar Spectrum
1015
1012
1014
1011
1013
1010
1012
109
108
120
130
140
150
Wavelength
Bill McClintock
SORCE Science Meeting
December 4 2003
160
170
180
1011
180
200
220
240
Wavelength
260
280
300
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SOLSTICE: Improvements over UARS
FUV: wavelength coverage extends
to 115nm with slightly improved
spectral resolution
Bill McClintock
SORCE Science Meeting
December 4 2003
MUV: resolution is about double with
greatly improved stellar throughput at
longer wavelengths
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SOLSTICE: Typical Time Series
SORCE observations scaled to the
Daily averaged Lyman Alpha fluxes
NOAA magnesium index
Bill McClintock
SORCE Science Meeting
December 4 2003
10
Solstice: In flight performance
Bill McClintock
SORCE Science Meeting
December 4 2003
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SOLSTICE: Flare Observations from 28 October 2003
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Bill McClintock
SORCE Science Meeting
December 4 2003
12
Flare Movie
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Bill McClintock
SORCE Science Meeting
December 4 2003
13
SOLSTICE: Get more details about SOLSTICE results
Posters at this meeting:
The Sun As Observed by SORCE SOLSTICE
William McClintock, Marty Snow, Gary Rottman, and Tom Woods
Solar Magnesium II Observations from SORCE SOLSTICE
Marty Snow, William McClintock, Gary Rottman, and Tom Woods
Posters at the SORCE AGU session:
In-Flight Performance of SORCE SOLSTICE
Marty Snow, William McClintock, Gary Rottman, and Tom Woods
Bill McClintock
SORCE Science Meeting
December 4 2003
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