The Sun As Observed by SORCE SOLSTICE
William McClintock, Marty Snow, Gary Rottman, and Tom Woods
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303
Mcclintock@lasp.colorado.edu
SH12A-1155
Improvements over
UARS SOLSTICE
SOLSTICE: The SOLar-STellar Irradiance Comparison Experiment
The SOLSTICE instrument observes both the sun and stars using the same
optical path A factor of ~108 in dynamic range is achieved by changing
apertures (~104), bandpass (~101), and exposure time (~103).
Lyman alpha
SORCE SOLSTICE Solar Spectrum
1015
C IV
1011
1010
Mg II
Science Objectives:
•Measure solar irradiance from 115 to 320 nm daily with a spectral resolution
of 0.5 nm and an accuracy better than 5%.
•Monitor solar irradiance variation with an accuracy of 0.5%.
•Establish the ratio of solar irradiance to the average flux of an ensemble of
bright, early-type stars with an accuracy of 0.5% for future studies of the longterm solar variability.
He II
Si III
1012
1014
Mg I
SORCE SOLSTICE Solar Spectrum
1013
In the FUV, the wavelength coverage has
been extended down to 115nm and the
resolution is slightly improved. This band
was called the “G” Channel on UARS.
1013
109
Measurements:
Wavelength Coverage:
Solar Spectral Resolution:
108
120
130
140
150
Wavelength
160
170
180
Stellar Spectral Resolution:
1012
115-320 nm
0.1 nm (FUV)
0.2 nm (MUV)
1.1 nm (FUV)
2.2 nm (MUV)
11
10
180
200
Solar-Stellar Comparison
Irradiance (photons/cm2/s/nm)
260
280
300
Model Solar Atmosphere (FAL99)
10000
Solar Irradiance
1014
240
Wavelength
Solar Variability Observations
Solar-Stellar Irradiance Comparison
1015
220
In the MUV, the resolution is about
double, and the stellar throughput is
greatly improved at longer wavelengths.
This band was called the “F” Channel on
UARS.
1013
1012
Eta UMa Irradiance (×109)
1011
8000
1010
109
108
150
200
Wavelength (nm)
250
300
The fundamental challenge of SOLSTICE is to measure
Irradiances to high accuracy over an enormous dynamic range.
The solar spectrum alone varies over 5 orders of magnitude in
the UV, and the stellar spectra are 9 orders of magnitude fainter
than the sun.
Observations of a carefully chosen set of non-variable
bright stars allows us to track changes in the
sensitivity of the instrument at the percent level over
arbitrarily long time intervals.
SOLSTICE Long Term Data Record
6000
4000
-500
0
500
1000
Height (km)
1500
2000
2500
The SORCE SOLSTICE has the advantage of direct heritage from UARS
SOLSTICE.
The light purple portion of the time series uses an extrapolated
degradation function. The star trackers on UARS failed in August 2000,
so stellar observations were no longer possible.
The gap in the SOLSTICE data record shown at left is only temporary.
Although the UARS platform has a number of end-of-life issues,
SOLSTICE has continued to take regular measurements of the solar
irradiance. However, these issues have made processing the data to high
quality standards difficult. The data processing system that produces
SORCE data will also process UARS data in the future, and the gap will
be filled in.
Note:
The gaps are due to current
reprocessing and are not
missing data.
Available data products include 1nm daily average Irradiance, 6-hour
averages, Mg II index, emission line Irradiances, and more.
Data Products are available at:
http://lasp.colorado.edu/sorce/data_access.html
The Irradiance measured by SOLSTICE probes many interesting regions of the solar atmosphere. Here is a small sample of lines and
the portion of the atmosphere that they sample. Model solar atmosphere shown here is from Fontenla et al., 1999, ApJ 518 480.