Greg Kopp's TSI Page

Updated 8 July 2017
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Current SORCE & TCTE Data Plots
TSI Climate Data Record
SORCE/TIM Mission Highlights
TIM Establishes Lower TSI Value
TIM Planetary Transit Observations
TIM Flare Detection in TSI
TIM References
Access the SORCE/TIM TSI data
Access the TCTE/TIM TSI data

Current SORCE & TCTE Data Plots

6-hourly averaged SORCE/TIM data are available since March 2003 (below, left or top) and TCTE/TIM data since Dec. 2013 (below, right or bottom)

SORCE/TIM and TCTE/TIM agree very well on an absolute scale. They were both calibrated independently at the component level 10 years apart.

TSI Climate Data Record

The TSI Climate Data Record now spans 38 years. Instrument offsets are unresolved calibration differences, much of which are due to internal instrument scatter (see Kopp & Lean 2011).

Data continuity via overlap from a series of instruments (below, left or top) allows adjustment to a common scale (below, right or bottom).

A new methodology to create a TSI composite has been defined by Dudok de Wit et al..

Unlike previous composites, which have been created by individual-instrument principal investigators and thus reflect biases toward their instruments, this methodology: The example composite shown below demonstrates the methodology applied to current TSI records. A future community-consensus composite using this technique will be created by a former ISSI and an existing SIST team with representatives from all current and most past TSI instruments.

Data are available here.

Correlations of TSI measurements with sunspot observations and active areas allow historical extrapolations of solar irradiances.
The historical reconstruction of TSI below is based on the NRLTSI2 model adjusted to the most recent SORCE/TIM TSI values.

Data are available here.

These estimated solar irradiances for the last 400 years are based on the NRLTSI2 historical TSI reconstruction model by J. Lean and described by Coddington et al. The values of the NRLTSI2 model have been offset a small amount for agreement with recent SORCE/TIM values and replaced by SORCE/TIM annual averages from 2003 onward. The historical reconstruction provided here was computed using TIM V.17 data in January 2017. It is updated annually as new TIM data are available or as improved historical reconstructions are created.

Changes to TSI reconstructions may be expected for two reasons:
1) The 2013 IPCC AR5 report used input solar forcing from the CMIP5, which is based on a prior version of the NRLTSI model. The IPCC AR6 CMIP6, however, uses both the empirical NRLTSI2 proxy-model and the semi-empirical SATIRE model. The reconstruction shown here is based only on the NRLTSI2 model. Of the NRLTSI2 and the SATIRE models, the NRLTSI2 reconstruction best matches the SORCE/TIM measurements as neither show the secular downward trend in TSI over the last three solar cycles that the SATIRE model (and thus CMIP6) does.
2) A revised sunspot record was released in 2015. Historical-TSI reconstructions based on this revised record suggest significant changes prior to 1885, which affect both the NRLTSI2 and the SATIRE reconstructions. (See Kopp, G., Krivova, N., Lean, J., and Wu, C.J., "The Impact of the Revised Sunspot Record on Solar Irradiance Reconstructions," Solar Physics, 2016, doi: 10.1007/s11207-016-0853-x for estimated changes.)

Coddington, O., Lean, J.L., Pilewskie, P., Snow, M., Lindholm, D.: 2015, A solar irradiance climate data record, Bull. American Meteorological Soc. doi: 10.1175/BAMS-D-14-00265.1

SORCE/TIM Mission Highlights

Key SORCE Discovery: The SORCE/TIM Determines a New, Lower Value of TSI Than Previous Measurements

Prior to the SORCE launch in 2003, on-orbit TSI instruments agreed with each other in measured TSI values near 1365 W/m^2 near solar minima. The new SORCE/TIM, including many optical, electrical, and calibration improvements over these prior instruments, measured values 0.35% lower than the other on-orbit instruments (see left-hand figure below). Initially disregarded by the community as an error in the TIM instrument, this difference has recently been shown to be due to uncorrected scatter causing erroneously high measurements by other instruments, all of which have an optical design that differs from the TIM by allowing two to three times the amount of light intended for measurement into the instrument. The TIM, placing the instrument's small precision aperture at the entrance, only allows the light intended for measurement into the instrument interior, and hence is much less susceptible to scattered light.
Diagnostics with the TSI Radiometer Facility (Kopp et al., SPIE, 2007) of ground-based instruments representative of those on orbit have demonstrated that the scatter in non-TIM instrument designs is the primary cause of the higher readings by the other instruments. Applying scatter corrections to these instruments' data brings their values down to those measured by the TIM, which reports a value of 1360.8 W/m^2 representative of the 2008 solar minimum (
Kopp & Lean, 2011) (see right-hand figure below). This new lower TSI value reported initially by the SORCE/TIM has also been validated with the recently launched PICARD/PREMOS (brown data in right-hand plot below) and the TCTE/TIM (blue data in right-hand plot below), both of which were calibrated on the TSI Radiometer Facility prior to launch.
TSI Record Prior to 2011 Corrections Being Applied to Non-TIM Instruments

Contemporary TSI Record Including TRF Corrections to Select Non-TIM Instruments

Planetary Transit Observations

The TIM measured a decrease in the TSI (red dots) as Venus transited the Sun on both 5-6 June 2012 and 8 June 2004. In agreement with predictions (grey curve) accounting for solar limb-darkening and the SORCE position, the incident sunlight dropped approximately 0.1% during the transits, which is comparable to the effect of a medium-sized sunspot. The gaps in the plotted data are from times when the SORCE spacecraft was in the Earth's shadow and could not view the Sun. Both 1st and 2nd Contacts, as Venus began its transit across the solar disk, were observed directly for both Venus transits. During the 2012 transit, egress (3rd and 4th Contacts) was also observed, although this occurred when the spacecraft was occulted by the Earth in 2004. The increases in brightness near ingress and egress during the transit are due to solar limb-darkening, which makes the center of the solar disk brighter than the edges and hence the transit-depth greater when Venus is nearer to disk-center. The small fluctuations in brightness on short timescales are from normal solar convection and oscillations, and can be seen in the un-occulted times both before and after the transits.
Exo-solar planets are being discovered via transits in front of their stars using similar photometric techniques.
(Published in Kopp, G., Lawrence, G., and Rottman, G., "The Total Irradiance Monitor (TIM): Science Results," Solar Physics, 230, 1, Aug. 2005, pp. 129-140.)
TIM Observations of 2012 Venus Transit

TIM Observations of 2004 Venus Transit

TIM Observations of 2016 Mercury Transit

Both the SORCE/TIM and the TCTE/TIM observed the 9 May 2016 Mercury transit. The high-cadence data from both instruments are combined and plotted in red below. During this transit, a modeled light-curve (grey) accounting for solar limb-darkening and the two spacecrafts' positions indicates that Mercury should decrease the sunlight at the Earth by up to 47 ppm (0.005%). This is a larger decrease than during either of the prior two Mercury transits, which were observed by the SORCE/TIM only. This decrease is suggestively discernable in the red TSI data despite the underlying continual solar variations, benefitting from the transit's larger net decrease, the TIM's precision, and the combination of both datasets. Averages of the TSI values from equal-duration times before, during, and after the transit (blue squares) indicate a measured decrease of 38 ppm (0.004%); although the uncertainties on this decrease are comparable to the value itself, so this really should not be considered a true planetary-transit "detection."
TIM Observations of 2006 Mercury Transit

The TIM viewed the Sun for the three SORCE orbits during which the 8 Nov. 2006 Mercury transit occurred. During this transit, Mercury decreased the sunlight at the Earth by up to 30 ppm (0.003%), indicated by the modeled light-curve (grey) that accounts for solar limb-darkening and the SORCE position. Even with the TIM's precision, this transit is not independently detectable in TSI because of the underlying continual solar variations, which have much greater amplitude. High cadence TIM measurements are shown in red with orbital averages and their standard deviations in blue. The spacecraft was in the Earth's shadow for both ingress and egress.
TIM Observations of 2003 Mercury Transit

The TIM also measured during the 7 May 2003 Mercury transit, which had a slightly larger effect than the 2006 transit. As the modeled light-curve (grey) indicates, Mercury decreased the sunlight at the Earth by 40 ppm (0.004%) at the peak of this transit. As with the 2006 observations, this transit is not readily apparent in TSI measurements alone because of the underlying solar variations. Again during this transit, the SORCE spacecraft was in the Earth's shadow for both ingress and egress. High cadence TIM measurements are shown in red with orbital averages and their standard deviations in blue.
(Published in Kopp, G., Lawrence, G., and Rottman, G., "The Total Irradiance Monitor (TIM): Science Results," Solar Physics, 230, 1, Aug. 2005, pp. 129-140.)

Total Flare Energy Measured in TSI

The TIM is the first TSI instrument with the sensitivity and low noise to report a solar flare detection in TSI (Kopp et al., AAS 2004; Woods et al., 2005). While flares are readily detectable at short wavelengths, where the Sun generally has relatively low signal, their contribution to the entire energy output from the Sun is almost negligibly small, making them extremely difficult to detect in TSI. Nevertheless, TSI observations provide a direct means of measuring the total radiant energy output from a flare, as these measurements integrate solar energy over all wavelengths.
The First Solar Flare Observed in TSI

NOAA/GOES reported peak X-ray (0.1-0.8 nm) values from the X17 flare at 11:10 UT on 28 Oct. 2003. The TIM measured a significant and sudden increase in TSI slightly prior to this, putting the TSI peak nearly in phase with the hard X-rays (as indicated by the derivative of the softer GOES X-rays). The abruptness of this increase and the following gradual decrease are typical of flares observed at EUV and X-ray wavelengths.
(Kopp et al., AAS 2004; Woods et al., 2005)
TIM Flare Measurements Provide Total Flare Energy

The TSI measurements of a flare provide the total, spectrally-integrated flare energy, which we estimate at 5e32 ergs for the 28 Oct. 2003 X17 flare.
(Kopp et al., AAS 2004; Woods et al., 2005)
Largest Short-Term Decrease in TSI

The passage of two large sunspot groups in late October 2003 caused a decrease in TSI larger than any short-term decrease in the 36-year TSI composite.

TIM References

Kopp, G.,
Earth's Incoming Energy: The Total Solar Irradiance, in Reference Module in Earth Systems and Environmental Sciences, Elsevier, 2016, ISBN 9780124095489.

T. Dudok de Wit, G. Kopp, C. Fröhlich, and M. Schöll, Methodology to create a new Total Solar Irradiance record: Making a composite out of multiple data records, Geophys. Res. Letters, doi:10.1002/2016GL071866, 2017.

Kopp, G., Magnitudes and Timescales of Total Solar Irradiance Variability, Journal of Space Weather and Space Climate, 6, A30, 11 pp., 2016, doi: 10.1051/swsc/2016025.

Kopp, G., Krivova, N., Lean, J., and Wu, C.J., The Impact of the Revised Sunspot Record on Solar Irradiance Reconstructions, Solar Physics, 15 pp., 2016, doi: 10.1007/s11207-016-0853-x.

Kopp, G., An Assessment of the Solar Irradiance Record for Climate Studies, Journal of Space Weather and Space Climate, 4, A14, DOI:10.1051/swsc/2014012, 2014.

Kopp, G., Fehlmann, A., Finsterle, W., Harber, D., and Heuerman, K., Total Solar Irradiance Data Record Accuracy and Consistency Improvements, Metrologia, 49, S29-S33, 2012.

Kopp, G. and Lean, J.L., A New, Lower Value of Total Solar Irradiance: Evidence and Climate Significance, Geophys. Res. Letters Frontier article, 38, L01706, doi:10.1029/2010GL045777, 2011.

Kopp, G., Heuerman, K., Harber, D., and Drake, V., The TSI Radiometer Facility - Absolute Calibrations for Total Solar Irradiance Instruments, SPIE Proc. 6677-09, 2007; doi:10.1117/12.734553.

Kopp, G. and Lawrence, G., The Total Irradiance Monitor (TIM): Instrument Design, Solar Physics, 230, 1, Aug. 2005, pp. 91-109.

Kopp, G., Heuerman, K., and Lawrence, G., The Total Irradiance Monitor (TIM): Instrument Calibration, Solar Physics, 230, 1, Aug. 2005, pp. 111-127.

Kopp, G., Lawrence, G., and Rottman, G., The Total Irradiance Monitor (TIM): Science Results, Solar Physics, 230, 1, Aug. 2005, pp. 129-140.

Kopp, G., Lawrence, G., and Rottman, G., Total Irradiance Monitor Design and On-Orbit Functionality, SPIE Proc. 5171-4, 2003, pp. 14-25.

Lawrence, G.M., Kopp, G., Rottman, G., Harder, J., Woods, T., and Loui, H., Calibration of the Total Irradiance Monitor, Metrologia 40, 2003, S78-S80.

Lawrence, G.M., Rottman, G., Kopp, G., Harder, J., McClintock, W., and Woods, T., "The Total Irradiance Monitor (TIM) for the EOS SORCE Mission," Earth Observing Systems V Proc. SPIE 4135-21, 2000, pp. 215-224.

Woods, T., Rottman, G., Harder, G., Lawrence, G., McClintock, B., Kopp, G., and Pankratz, C., "Overview of the EOS SORCE Mission," SPIE 4135, 2000, pp. 192-203.

Lawrence, G.M., Rottman, G., Harder, J., and Woods, T., The Solar Total Irradiance Monitor:TIM, Metrologia 37, 2000, pp. 407-410.