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Figure 1: SATIRE-S daily TSI values (grey) and 121-days running mean (horizontal line at 1360.75 W/m² to illustrate the change in solar minima). Figure 2: NRLTSI2 daily values (grey) and 121-days running mean (horizontal line at 1360.45 W/m² to illustrate the stability of the solar minima). Only data onward of 1976 are shown. Figure 3: Timeseries of SATIRE-S (red) and NRLTSI2 (black) TSI reconstruction models after 121-days running mean. The daily NRLTSI2 values are shown in grey. Horizontal line at 1360.75 W/m² illustrates the change in solar minima. Figure 4: (rescaled) ERB timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 5: (rescaled) ACRIM1 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 6: ERBS timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 7: (rescaled) ACRIM2 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 8: (rescaled) DIARAD timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 9: PMO06 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. Figure 10: (rescaled) ACRIM3 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Some outliers are in red. Figure 11: (rescaled) TIM/SORCE timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 12: (rescaled) SOVA/Picard timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 13: (rescaled) PREMOS timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 14: (rescaled) TIM/TCTE timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 15: (rescaled) TIM/TSIS-1 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Figure 16: Timeseries of individual TSI measurements after selection and harmonization. A 121-day running mean is used to remove the short-term solar noise. The 1361 W/m² horizontal line is shown to illustrate the stability between the solar minima. Figure 17: Illustration of the gap filling process. The black curve is an original TSI record with many data gaps (in this example the TIM/TCTE in 2014). The green curve is the SATIRE-S model. The red curve shows how the gaps can be filled by mixing the incomplete record with the (complete) SATIRE-S record. Figure 18: C3S composite daily TSI values (grey) and 121-day running mean (red). The NRLTSI2 model, with an offset of 0.31 W/m² to match the curves, is shown in black. |
General definitions
Term | Definition | ||||
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Earth Radiation Budget (ERB) | The difference between the incoming radiant energy to the Earth (directly dependent on the TSI) and the outgoing radiant energy due to reflection and thermal emission. | ||||
Electrical substitution cavity radiometer | Radiant energy measurement principle in which the radiant energy absorbed in a cavity is equilibrated with electrical power dissipated in a second non-illuminated equivalent cavity. | ||||
Magnetogram | Image of the Sun showing the strength and the polarity of its magnetic fields. The image is taken by an instrument called magnetograph. | ||||
Scattering and diffraction | Change of light direction due to interaction with matter. The diffraction is a spreading of light without changing in the average direction, while scattering is the deflection of the light with a clear change of direction. | ||||
Astronomical Unit (A.U.) | Unit of length equal to the mean distance between the center of the Earth and the center of the Sun. | ||||
Irradiance | Flux of radiant energy per unit area. The irradiance is usually expressed in W/m² unit. | ||||
Solar cycles | The solar cycles are nearly periodic 11-year changes in the Sun's activity. | ||||
Solar minima, quiet Sun | The 11-year solar cycle is characterized by periods of least solar activity called solar minima or quiet Sun. During these periods the average TSI is also minimum. | ||||
Bright facula | A solar facula is a bright spot in the photosphere. This part of the Sun disk has higher TSI than its surrounding area. | ||||
Dark sunspot | Opposite to a facula, a sunspot is a part of the Sun disk that appears darker, i.e. with a lower TSI, than its surrounding area. The sunspots can be decomposed in two main regions: the central umbra (with the lowest TSI) and the surrounding penumbra (with higher TSI than in the central umbra). The sunspots are often organized in network. | ||||
Bias
| The bias (b) is the average value of the difference of the data (xi ) with respect to a reference dataset (ri ), where N is the number of data points:
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Climate Data Store (CDS) | The front-end and delivery mechanism for data made available through C3S. | ||||
Climate Data Record (CDR) | Sufficiently long, accurate and stable time series of a climate variable to be useful to address climate variability and change. | ||||
Interim Climate Data Record (ICDR) | An interim CDR is an extension of a CDR that meets some timeliness requirements needed in some applications, e.g. for use in the "State of the Climate" reports. These preliminary data might not be fully validated and may need to be reprocessed before inclusion in the finale CDR. |
Scope of the document
This document is the Algorithm Theoretical Basis Document (ATBD) for the generation of the version 3 of the Climate Data record (CDR) and Interim Climate Data Record (ICDR) v3.1 of daily Total Solar Irradiance (TSI) for the Copernicus Climate Change Service (C3S).
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Relative variations of the TSI in phase with the 11-year solar cycle of the order of 1 W/m² are now well established, as summarized by Dewitte & Nevens (2016) [D1] and Dewitte & Clerbaux (2017) [D2]. Apart from these true TSI variations, differences in the absolute level well above 1 W/m² are observed between the different instruments indicating limitations of the absolute accuracy. For this reason, multiplicative correction factors are determined to scale all the timeseries to a same radiometric level. These factors are determined by optimizing the consistency over the overlap periods that exist between the different instruments. Still, a reference level must be defined and this is done in this work in such a way that the average of the correction factors for the 5 most accurately calibrated instruments is set to 1.0. These 5 instruments are: Physikalisches und Meteorologisches Observatorium 06 (PMO06), Precision Monitor Sensor (PREMOS), and the TIM instruments on the Solar Radiation and Climate Experiment (TIM/SORCE), on the Total solar irradiance Calibration Transfer Experiment (TIM/TCTE), and on the International Space Station (TIM/TSIS1).
Table 1: Total Solar Irradiance space instruments (acronyms definitions in footnote). The instruments used in the C3S v3.0 and v3.1 daily TSI composite are highlighted in bold. Anchor table1 table1
Instrument 1 | Platform(s) | Used | Operation period(s) | References |
TCFM | Mariner-6 & 7 | No | 1969 | Plamondon (1969) |
ERB | Nimbus 6 | No | 1975 | Hickey et al (1976) |
Nimbus 7 | Yes | 1978 - 1993 | Hickey et al (1980) | |
ACRIM 1 | SMM | Yes | 1980-1989 | Willson et al. (1980) |
Solcon 1 | Spacelab 1 | No | 1983 | Crommelynck et al (1987) |
ERBE | ERBS | Yes | 1984-2003 | ERBE (1986) |
NOAA-9 | Yes | 1985-1989 | ||
ACRIM 2 | UARS | Yes | 1991-2001 | Willson (1994) |
Solcon 2 | Atlas 1 | No | 1992 | Crommelynck et al (1994) |
Sova 1 | Eureca | No | 1992-1993 | |
Sova 2 | Eureca | No | 1992-1993 | Romero et al. (1994) |
ISP-2 | Meteor-3 No 7 | No | 1994 | Sklyarov et al. (1996) |
DIARAD/VIRGO | SOHO | Yes | 1996-present | Dewitte et al. (2004) |
PMO06V-A/VIRGO | SOHO | Yes | 1996-present | Froehlich et al. (1997) |
ACRIM 3 | ACRIMSAT | Yes | 2000-2014 | Willson et al. (2003) |
TIM | SORCE | Yes | 2003-2020 | Kopp et al. (2005) |
DIARAD/SOVIM | ISS | No | 2008 | Mekaoui et al. (2010) |
SIM | FY 3A | No | 2008-2015 | Fang et al. (2014) |
SOVA | Picard | Yes | 2010-2014 | Dewitte et al. (2013a) |
PREMOS | Picard | Yes | 2010-2014 | Schmutz et al. (2012) |
SIM | FY 3B | No | 2011-present | Fang et al. (2014) |
TIM | TCTE | Yes | 2013-2019 | Kopp et al. (2016) |
SIM | FY 3C | No | 2013-present | Wang et al. (2017) |
TIM | TSIS-1 | Yes | 2018- present | Kopp, G. (2020), |
CLARA | NorSat | No | 2018- present | Walter et al. (2017) |
DARA | PROBA-3 | No | To be launched |
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• The NRLTSI2 record is explicitly not used when constructing the C3S v3.0 and v3.1 daily TSI composites, so it can be used as independent source for the validation (see methodology and results in PQAD [D3] and PQAR [D5] documents).
2.1.1 SATIRE-S
The SATIRE-S (Spectral And Total Irradiance Reconstructions, Yeo et al, 2014a and 2014b) is a reconstruction of the TSI over the 1974-present-day period using full-disc magnetograms and continuum images of the Sun. It uses the data from the National Solar Observatory Photospheric magnetogram (NSO KP) (1974-1999), SOHO/ Michelson Doppler Imager (MDI) (1999-2009) and Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) (since 2010). These observations allow for the estimation of the fractional coverage of: quiet Sun, sunspot umbrae, sunspot penumbrae, faculae and network. A regression between these indices and the TSI is then derived and used in the reconstruction. The SATIRE-S data starts on 23rd August 1974 and provides data until 8th July 2023 (at time of writing). New data are regularly added to the timeseries.
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SATIRE-S | ||||||||
Full name: Spectral And Total Irradiance Reconstructions | ||||||||
Organization: Max-Planck-Institut für Sonnensystemforschung (MPI for Solar System Research) | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
23.08.1974 – 08.07.2023 | 01.01.1979 – 06.11.1980 | Set to 1.00015 | ||||||
Data availability | C3S Data availability (filled) | C3S estimated noise level | ||||||
100% | 100% (100%) | Set to 0.5 W/m² | ||||||
Figure 1: SATIRE-S daily TSI values (grey) and 121-days running mean (horizontal line at 1360.75 W/m² to illustrate the change in solar minima). | ||||||||
DATA SOURCE: http://www2.mps.mpg.de/projects/sun-climate/data_body.html | ||||||||
References: Yeo et al. (2014a), Yeo et al. (2014b). | ||||||||
Notes:
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2.1.2 NRLTSI2
NRLTSI2 is the version 2 of the Naval Research Laboratory’s (NRL) solar variability models for Total Solar Irradiance (TSI). This CDR was created at the Space Science Division of the Naval Research Laboratory (NRL) in collaboration with the Laboratory for Atmospheric and Space Physics (LASP) of the University of Colorado. The NRLTSI2 CDR is published as part of the NOAA CDR Program and is documented by Coddington et al. (2015, 2016). In this model, the daily TSI is estimated from the observation of the bright faculae and the dark sunspots on the solar disk. A linear regression between these proxies of solar activity and the TIM/SORCE TSI was established and used in the reconstruction. The model assumes a quiet Sun TSI of 1360.45 W/m² (Kopp and Lean, 2011) as estimated from the TIM/SORCE measurement at solar minimum. The reconstruction starts on 1st January 1882 and provides data until 31st December 2022 (at time of writing). New data are regularly added to the timeseries, on a quarterly basis.
NRLTSI2 | ||||||||
Full name: Naval Research Laboratory Total Solar Irradiance version 2 | ||||||||
Organization: U.S. Naval Research Laboratory | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
01.01.1882 – 31.12.2022 | Not used in the composite | (not applicable) | ||||||
Data availability | C3S Data availability (filled) | C3S estimated noise level | ||||||
100% | 100% (100%) | (not applicable) | ||||||
Figure 2: NRLTSI2 daily values (grey) and 121-days running mean (horizontal line at 1360.45 W/m² to illustrate the stability of the solar minima). Only data onward of 1976 are shown. | ||||||||
DATA SOURCE: | ||||||||
References: Coddington et al. (2015), Coddington et al. (2016). | ||||||||
Notes:
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2.1.3 SATIRE-S / NRLTSI2 intercomparison
Figure 3 shows the SATIRE-S and NRLTSI2 timeseries over the 1975 – 2022 time period. The 2 models show very close agreement over solar cycle 23 (1996 – 2008) but otherwise exhibit significant differences, especially in the level of the solar minima in 1986, 1996 and 2019.
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Note about the graphs in Figure 4 to Figure 15 : the graphs show the timeseries of the satellite record (in green the daily and orange the 121-days running mean) after rescaling to the C3S record (in black). The NRLTSI2 data is also shown (in brown) after a rescaling on the same overlap period. The parts of the satellite record which are discarded in the C3S composite are in red (daily) and blue (121-days running mean).
2.2.1 ERB on NIMBUS7
ERB on Nimbus 7 | ||||||||
Full name: Earth Radiation Budget on NIMBUS7 | ||||||||
Organization: NASA / NOAA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
16.11.1978 – 13/12/1993 | 01.01.1981 – 31.12.1989 | 0.992447 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
83.24% | 89.45% (100% ) | 0.318 W/m² | ||||||
Figure 4: (rescaled) ERB timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
References: Hickey et al. (1980) | ||||||||
Notes:
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2.2.2 ACRIM1 on SMM
ACRIM1 on SMM | ||||||||
Full name: Active Cavity Radiometry Irradiance Monitor on Solar Maximum Mission | ||||||||
Organization: NASA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
16.02.1980 – 14.07.1989 | 07.11.1980 – 14.07.1989 | 0.995568 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
90.14 % | 90.00% (97.96%) | 0.270 W/m² | ||||||
Figure 5: (rescaled) ACRIM1 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 2 : http://acrim.com/RESULTS/data/acrim1/acrim1_hdr.rtf | ||||||||
References : Willson et al. (1981) | ||||||||
Notes:
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2.2.3 ERBS
ERBS | ||||||||
Full name: Earth Radiation Budget Satellite solar monitor | ||||||||
Organization: NOAA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
17.12.1984 – 23.04.2003 | 02.07.1987 - 06.02.2001 | 0.997149 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
98.46% | 97.93% ( 100%) | 0.270 W/m² | ||||||
Figure 6: ERBS timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 3 : An application, such as FileZilla, WinSCP or Wget, might be needed to open FTP sites.: ftp://ftp.ngdc.noaa.gov/STP/SOLAR_DATA/SOLAR_IRRADIANCE/ERBS2003.TXT | ||||||||
References: ERBE (1986) | ||||||||
Notes:
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2.2.4 ACRIM2
ACRIM2 | ||||||||
Full name: Active Cavity Radiometry Irradiance Monitor on Upper Atmosphere Research Satellite | ||||||||
Organization: NASA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
04.10.1991 – 05.05.2001 | 04.10.1991 – 05.05.2001 | 0.997821 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
93.35% | 93.35% (100%) | 0.215 W/m² | ||||||
Figure 7: (rescaled) ACRIM2 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 4 : http://acrim.com/RESULTS/data/acrim2/dayu2deg_ts_0110041651_hdr.txt | ||||||||
References: Willson (1994) | ||||||||
Notes:
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2.2.5 DIARAD / VIRGO on SOHO
DIARAD / VIRGO on SOHO | ||||||||
Full name: Differential Absolute Radiometer on Variability of Irradiance and Gravity Oscillations | ||||||||
Organization: RMIB | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
18.01.1996 - present | 01.01.1997 – present | 0.996449 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
93.95% | 93.78% (98.33%) | 0.121 W/m² | ||||||
Figure 8: (rescaled) DIARAD timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 5 : http://remotesensing.oma.be/meteo/view/en/3385923-diarad.level2.web.html | ||||||||
References: Dewitte et al. (2004) | ||||||||
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2.2.6 PMO06 on VIRGO
PMO06 on VIRGO | ||||||||
Full name: Physikalich Meteorologisches Observatorium version 06 | ||||||||
Organization: Physikalich-Meteorologisches Observatorium Davos and World Radiation Center | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
21.02.1996 – 13.05.2022 | 01.01.1997 – 13.05.2022 | 1.000181 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
97.87% | 97.83% (98.88%) | 0.173 W/m² | ||||||
Figure 9: PMO06 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. The parts discarded are in red and blue. | ||||||||
DATA SOURCE 6 : ftp://ftp.pmodwrc.ch/pub/data/irradiance/virgo/TSI/VIRGO_TSI_Daily_V8_20230728.zip | ||||||||
References: Froehlich et al. 1997 | ||||||||
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2.2.7 ACRIM3
ACRIM3 | ||||||||
Full name: Active Cavity Radiometry Irradiance Monitor on ACRIMSAT | ||||||||
Organization: NASA | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
05.04.2000-05.03.2013 | 05.04.2000-05.03.2013 | 1.000078 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
97.44% | 97.44% (100%) | 0.126 W/m² | ||||||
Figure 10: (rescaled) ACRIM3 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. Some outliers are in red. | ||||||||
DATA SOURCE 7 : http://acrim.com/RESULTS/data/acrim3/daya2sddeg_ts4_Nov_2013_hdr.txt | ||||||||
References: Willson et al. (2003) | ||||||||
Notes:
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2.2.8 TIM on SORCE
TIM on SORCE | ||||||||
Full name: Total Irradiance Monitor (TIM) on SOlar Radiation and Climate Experiment (SORCE) | ||||||||
Organization: Laboratory for Atmospheric and Space Physics (LASP) | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
25.02.2003 – 25.02.2020 | (All) | 1.000256 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
94.72% | 94.72% (96.62%) | 0.089 W/m² | ||||||
Figure 11: (rescaled) TIM/SORCE timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: http://lasp.colorado.edu/data/sorce/tsi_data/daily/sorce_tsi_L3_c24h_latest.txt | ||||||||
References : Kopp et al. (2005) | ||||||||
Notes:
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2.2.9 SOVA on Picard
SOVA on Picard | ||||||||
Full name: SOlar VAriability Experiment on Picard | ||||||||
Organization: RMIB | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
27.08.2010 – 03.11.2013 | 27.08.2010 – 03.11.2013 | 0.999345 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
80.43% | 80.43% (100%) | 0.145 W/m² | ||||||
Figure 12: (rescaled) SOVA/Picard timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: http://idoc-picard.ias.u-psud.fr:8182/sitools/upload/sovap-data.dat | ||||||||
Reference : Dewitte et al. (2013a) | ||||||||
Notes:
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2.2.10 PREMOS on Picard
PREMOS on Picard | ||||||||
Full name: Precision Monitor Sensor on Picard | ||||||||
Organization: Physikalich-Meteorologisches Observatorium Davos and World Radiation Center | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
27.07.2010 – 20.08.2013 | 27.07.2010 – 20.08.2013 | 1.000256 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
90.19% | 90.19% ( 100%) | 0.086 W/m² | ||||||
Figure 13: (rescaled) PREMOS timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: (daily and hourly data, see note here after) | ||||||||
References : Schmutz et al. (2012) | ||||||||
Notes:
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2.2.11 TIM on TCTE
TIM on TCTE | ||||||||
Full name: Total Irradiance Monitoring on Total Solar Irradiance Calibration Transfer Experiment | ||||||||
Organization: Laboratory for Atmospheric and Space Physics (LASP) | ||||||||
Period covered | C3S period selected | C3S adjustment factor | ||||||
16.12.2013 – 15.05.2019 | 16.12.2013 – 15.05.2019 | 0.999771 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
83.46% | 83.46% (93.98%) | 0.092 W/m² | ||||||
Figure 14: (rescaled) TIM/TCTE timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: http://lasp.colorado.edu/data/sorce/tsi_data/daily/sorce_tsi_L3_c24h_latest.txt | ||||||||
References : Kopp et al. (2016), (TCTE 2014) | ||||||||
Notes and references:
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2.2.12 TIM on TSIS-1
TIM on TSIS-1 | ||||||||
Full name: Total Irradiance Monitor on TSIS | ||||||||
Organization: Laboratory for Atmospheric and Space Physics | ||||||||
Period covered | C3S period selected | adjustment factor | ||||||
11.01.2018 – present | 11.01.2018 – present | 0.999535 | ||||||
Data availability | Data availability (gap filled) | C3S estimated noise level | ||||||
86.30% | 86.30% (100%) | 0.076 W/m² | ||||||
Figure 15: (rescaled) TIM/TSIS-1 timeseries (green and orange) with C3S CDR (black) and NRLTSI2 (brown) models. | ||||||||
DATA SOURCE: http://lasp.colorado.edu/data/tsis/tsi_data/tsis_tsi_L3_c24h_latest.txt (version 4 is used) | ||||||||
References : Kopp (2020) | ||||||||
Notes:
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Table 2 : Scaling factors and precision estimates (see Section 3.2) for the 12 input TSI timeseries. Anchor table2 table2
| Instruments | Scaling factor
(unitless) | Precision
(W/m²) | ||||||
1 | ERB/NIMBUS7 | 0.992447 | 318 | ||||||
2 | ACRIM1 | 0.995568 | 270 | ||||||
3 | ERBS | 0.997149 | (0.039) 0.270 | ||||||
4 | ACRIM2 | 0.997821 | 215 | ||||||
5 | DIARAD/VIRGO | 0.996449 | 121 | ||||||
6 | PMO06/VIRGO | 1.000181 | 173 | ||||||
7 | ACRIM3 | 1.000078 | 126 | ||||||
8 | TIM/SORCE | 1.000256 | 89 | ||||||
9 | SOVA/PICARD | 0.999345 | 145 | ||||||
10 | PREMOS/PICARD | 1.000256 | 86 | ||||||
11 | TIM/TCTE | 0.999771 | 92 | ||||||
12 | TIM/TSIS-1 | 0.999535 | 76 | ||||||
S | SATIRE-S in 1979-1980 | 1.000150 | - |
Figure 16 shows the resulting scaled TSI records for the individual instruments. For clarity we use a 121-days running mean to remove the short term solar noise, and to highlight the instrumental differences. After scaling, the instruments agree in general quite well, except at the very beginning of the record and for 2018 onward. Figure 16 also shows that the ERBS instrument is critical to fill the so-called ACRIM gap (15.07.1989 – 03.10.1991), it is the only TSI instrument that was monitoring the TSI during this period.
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As some instruments (PREMOS and SOVAP) have not observed during low activity periods, it is decided to use the ‘RMS max’ column as an estimation of the instrument precision. For the ERBS timeseries, the estimated precision is not realistic (due to the use of SATIRE-S in the gap filling). It is then decided to use the ACRIM1 precision as estimate for the ERBS record, as both missions used the same radiometric cavity.
Table 3: Instrument precision estimated as root mean square (RMS) difference with SATIRE-S. The columns 'max' and 'min' correspond respectively to periods of high and low solar activity. The column ‘all’ does not involve any selection based on solar activity. Anchor table3 table3
| Instruments | RMS max | RMS all | RMS min | ||
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1 | ERB/NIMBUS7 | 0.318 | 0.270 | 0.263 | ||
2 | ACRIM1 | 0.270 | 0.184 | 0.128 | ||
3 | ERBS | (0.039) 0.270 | (0.037) 0.184 | (0.035) 0.128 | ||
4 | ACRIM2 | 0.215 | 0.187 | 0.139 | ||
5 | DIARAD/VIRGO | 0.121 | 0.103 | 0.064 | ||
6 | PMO06/VIRGO | 0.173 | 0.142 | 0.079 | ||
7 | ACRIM3 | 0.126 | 0.111 | 0.064 | ||
8 | TIM/SORCE | 0.089 | 0.071 | 0.035 | ||
9 | SOVA/PICARD | 0.145 | 0.145 | - | ||
10 | PREMOS/PICARD | 0.086 | 0.086 | - | ||
11 | TIM/TCTE | 0.092 | 0.073 | 0.039 | ||
12 | TIM/TSIS-1 | 0.076 | 0.057 | 0.031 |
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Many of the input records have gaps in the daily TSI values. It is the case with the ERB (Nimbus7) and ERBS (ERBE) measurements at the beginning of the composite and also of the TSIS-1 instrument at the end of the composite. In the C3S v3.0 and v3.1 daily TSI composite, a gap filling mechanism is implemented as a preprocessing of the original timeseries. A gap is filled provided it extends over less than 50 days.
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Table 4: General characteristics of the C3S daily TSI composite CDR. Anchor table4 table4
General characteristics of the CDR | |
Temporal resolution | daily mean |
Time period | CDR v3.0: 1st January 1979 to 31st of December 2020 ICDR: 1st January 2021 onward v3.1: 1st January 2021 – 30th September 2023 |
Format | ASCII |
Filenames | C3S_RMIB_daily_TSI_composite_TCDR_v3.0.txt C3S_RMIB_daily_TSI_composite_ICDR_v3.1.txt |
The Total Solar Irradiance is the spectrally integrated total amount of radiant energy coming from the Sun per square meter of surface, perpendicular to the sunlight, at 1 astronomical unit.
Table 5: Total Solar Irradiance parameter. Anchor table5 table5
Total Solar Irradiance | |
long_name | Total Solar Irradiance, daily Means |
standard_name | Total Solar Irradiance |
CF_name | solar_irradiance |
units | W/m². |
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Chapman, G. A., Cookson, A. M., and Dobias, J. J. (1996): Variations in total solar irradiance during solar cycle 22, J. Geophys. Res., 101(A6), 13541– 13548, https://www.doi.org/10.1029/96JA00683.
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