Solar Spectral Irradiance Data
- Available SSI Data Summary Table/Data Access
- Reading SORCE SSI Data Product Files
- Data Product Description
- Data Quality Description: XPS, SIM, SOLSTICE
- Instrument Description
- Data File Organization
- Scientific Contacts
- Research and Applications
Available SSI Data Summary Table/Data Access
The following readers are available for the data files in the table above:
- SSI Level 3 text file reader (code in IDL)
- XPS Level 4 NetCDF file reader/plotter
(zip file, code in IDL)
The SORCE SOLSTICE, SIM, and XPS instruments together provide measurements of the full-disk Solar Spectral Irradiance (SSI) from 0.1 nm to 2400 nm (excluding 34-115 nm, which is not covered by the SORCE instruments). The two SOLSTICE instruments measure spectral irradiance from 115 nm to 310 nm with a resolution of 1 nm, the SIM instrument measures spectral irradiance from 310 nm to 2400 nm with a resolution varying from 1 to 34 nm, and the XPS instrument measures six broadband samples from 0.1 to 34 nm and at Lyman-alpha (121.6 nm). Measurements from these instruments are combined into merged daily and 6-hourly* spectra (*6-hourly data is currently available for the XPS instrument only and may be available from the other spectral instruments in the future), each containing representative irradiances reported on a uniform wavelength scale, which varies from 1-34 nm over the entire spectral interval. Irradiances are reported at a mean solar distance of 1 astronomical unit (AU) with units of W/m2/nm.
Please feel free to contact the appropriate member of the SORCE science team (see below) if you have any questions or concerns regarding the quality or usage of the SORCE data.
Please be aware of the following considerations concerning the SORCE spectral data products, whose contents include
data from the XPS, SIM, and SOLSTICE instruments. Also be aware that some of the SORCE data still exhibit instrumental artifacts.
We will be quite pleased to assist you with the correct interpretation of features exhibited within the SORCE data products.
- On-orbit instrument characterization is an ongoing effort, and the XPS team checks photometer degradation using redundant channels and underflight calibration rockets funded by TIMED SEE.
- Only the XPS Lyman-a (121.5 nm) channel has shown any degradation, being about 10% the first year and then slowing down with time.
- The XPS algorithms changed in 2006 in response to the XPS filter anomaly in December 2005, and only minor updates are anticipated for the extended mission.
- The accuracy of the XPS Level 2 irradiance is 12%-26%, photometer dependent.
- There is additional uncertainty for applying the spectral model for the XPS Level 4 irradiances, and this estimated accuracy is 30% for the integrated XUV irradiance. The spectral distribution in the XPS Level 4 is from the CHIANTI model and not from direct measurements from XPS, a set of broadband photometers.
- The spectral distribution above 27 nm has been validated with the TIMED SEE EGS (27-194 nm, 0.4 nm resolution) measurements, so there is good confidence in the spectral distribution shortward of 27 nm.
Please use the products available with caution; be aware that these data may exhibit some data gaps, as well as instrumental (non-solar) artifacts, as described below. The SORCE science team is continually working on improvements to these data products, and is very interested in receiving comments and feedback from users of the data products.
- Certain instrumental artifacts are still present within the data and a few on-orbit instrument calibrations are not yet applied. The SIM team is actively working on these issues.
- Absolute Accuracy: An important factor (ESR absorptivity) is being characterized and is not yet applied to the SIM data. As a result, the absolute accuracy of SIM data at visible wavelengths is 2% or better. In the infrared, native SIM data are estimated to be low by about 10%. Currently, however, a smooth correction is applied to the data bringing the SIM data into agreement with the SOLSPEC and SRPM spectra. This correction is in accord with the current laboratory studies.
- Relative Accuracy: The uncertainties reported with the data provide an indicator of relative precision. Above 500 nm, relative accuracy is better than approximately 300 ppm. Below 500 nm, relative accuracy decreases to approximately 0.5% at 310 nm.
- Wavelength Scale: SIM wavelengths (210-2400 nm) are presently estimated to be accurate to 0.02 nm ± &lambda*1.5×10-4 (0.05 – 0.2 nm), depending on wavelength (more accurate at shorter wavelengths). Relative (day-to-day) accuracy is much better.
The SOLSTICE data are routinely being processed with updated degradation (version 10).
- Absolute Accuracy: (See McClintock et. al 2005 calibration paper, pg. 288 for details.)
- FUV (115-180 nm): Varies from ~6% at shortest wavelengths to ~2% at longer wavelengths.
- MUV (180-310 nm): ~3% at wavelengths <300 nm; ~6% longward of 300 nm.
- Relative Accuracy:
- FUV (115-180 nm) – Estimated to be about 0.5% per year
- MUV (180-310 nm) – Estimated to be about 0.2%-2.6% per year
- A scattered light correction needs to be applied to the data, which will provide a ~1% effect at some wavelengths.
- Temperature Gain – In-flight characterization data has been applied with minimal effect and is being improve to further reduce the instrument’s susceptibility to detector temperature changes. This is a small effect.
- Data prior to May 2003 exhibit instrument artifacts that are apparently related to instrument pointing. These data are being withheld until an appropriate correction can be applied.
- MUV measurements (180-310 nm) made after late January, 2006 exhibit a pointing-related discontinuity that is associated with an instrument mechanism anomaly. A correction has been applied but a small discontinuity remains at some wavelengths. Further analysis is ongoing.
- The instrument misalignment appears to be a function of time that has not been fully modeled. Further analysis is ongoing.
- The field of view sensitivity maps appear to be introducing moderate uncertainties. Further analysis is ongoing.
For a complete description of the SORCE instruments, please visit the instrument home page:
Because of selective absorption and scattering processes in the Earth’s atmosphere, different regions of the solar spectrum affect Earth’s climate in distinct ways. Approximately 20-25% of the Total Solar Irradiance (TSI) is absorbed by atmospheric water vapor, clouds, and ozone, by processes that are strongly wavelength dependent. Ultraviolet radiation at wavelengths below 300 nm is completely absorbed by the Earth’s atmosphere and contributes the dominant energy source in the stratosphere and thermosphere, establishing the upper atmosphere’s temperature, structure, composition, and dynamics. Even small variations in the Sun’s radiation at these short wavelengths will lead to corresponding changes in atmospheric chemistry. Radiation at the longer visible and infrared wavelengths penetrates into the lower atmosphere, where the portion not reflected is partitioned between the troposphere and the Earth’s surface, and becomes a dominant term in the global energy balance and an essential determinant of atmospheric stability and convection.