Contributors: A. Velazquez Blazquez (Royal Meteorological Institute of Belgium (RMIB)), N.Clerbaux (RMIB)
Issued by: RMIB/Nicolas Clerbaux
Date: 24/11/2023
Ref: C3S2_D312a_Lot1.2.2.6-v1.0_202303_PUGS_ECVEarthRadiationBudget_v1.1
Official reference number service contract: 2021/C3S2_312a_Lot1_DWD/SC1
History of modifications
List of datasets covered by this document
Related documents
Acronyms
List of tables
List of figures
General definitions
Term | Definition |
Total Solar Irradiance (TSI) | The Total Solar Irradiance (TSI) quantifies the total amount of solar energy that is received by the Earth. It is defined per unit surface perpendicular to the Sun–Earth direction at the mean Sun–Earth distance. The TSI is a fundamental variable governing the climate system, and is recognized as Essential Climate Variable (ECV) by the Global Climate Observing System (GCOS). |
Climate Data Store (CDS) | The front-end and delivery mechanism for data made available through C3S |
Earth Radiation Budget | 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. |
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 | An interim CDRs is an extension of a CDR that meets some timeliness requirements needed in some applications (e.g. “State of the Climate” reports). These preliminary data might not be fully validated and may need to be reprocessed before inclusion in the CDR. |
Astronomical unit | 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 (usually expressed in W/m² unit). |
Scope of the document
This document is the Product User Guide and Specifications (PUGS) for the third version (v3.0) of the daily Total Solar Irradiance (TSI) timeseries which is generated and published as part of the Copernicus Climate Change Service (C3S), and subsequent ICDR extensions of the product time series (v3.x). It provides the minimum information a user should need for an appropriate use of the TSI data available through the C3S Climate Data Store (CDS).
Executive summary
The Total Solar Irradiance (TSI) quantifies the amount of solar energy that is received by the Earth. It is defined as the amount of solar power that reaches the Earth per unit surface perpendicular to the Sun–Earth direction at the mean Sun–Earth distance. The TSI is a fundamental variable governing the climate system, and is recognized as an Essential Climate Variable (ECV) by the Global Climate Observing System (GCOS).
Within the Copernicus Climate Change Service (C3S), a long composite Climate Data Record (CDR) is constructed from different TSI measurements obtained by an ensemble of space instruments that have observed the Sun since the 1970’s. In the v3 version, the composite starts on 1/1/1979 and provides daily value of the TSI. To create the composite, the measurements of the individual instruments are first put on a common absolute scale, and their quality is assessed by intercomparison. Then, the composite time series is an average of all available measurements, on a daily basis.
Section 1 presents a description of the product, with the list of the instruments used in the generation of the datasets. In addition, there's all the information related to the format and requirements of the product, with an example of a dataset. Section 2 presents all the information related to the access of the data and the data sources.
1. Composite daily Total Solar Irradiance CDR
1.1 Product description
The Total Solar Irradiance (TSI) quantifies the amount of solar energy that is received by the Earth. The TSI is defined as the amount of solar power that reaches the Earth’s top of the atmosphere per unit surface area perpendicular to the Sun–Earth direction at the mean Sun–Earth distance. It is a fundamental variable governing the climate system, and is recognized as an ECV by the Global Climate Observing System (GCOS). Within the Copernicus Climate Change Service (C3S), a composite Climate Data Record (CDR) is constructed from measurements of the TSI assessed by an ensemble of space instruments.
The first Total Solar Irradiance (TSI) measurements from space were made with the Temperature Control Flux Monitor (TCFM) on Mariner 6 and 7 (Plamondon, 1969). Following this, continuous measurement of the TSI started with the Earth Radiation Budget (ERB) instrument on Nimbus 7 (Hickey et al., 1980). Then continuous monitoring with an ageing corrected TSI instrument started with the Active Cavity Radiometer Irradiance Monitor (ACRIM1) instrument on the Solar Maximum Mission (SMM) (Willson et al., 1980). Since these early missions, TSI measurements have been continued with several space instruments listed in Table 1-2 (reproduced from ATBD [D1]).
The daily TSI composite is constructed by scaling the individual series to a common absolute level as described in the ATBD [D1]. An important part is the definition of this reference level. In the version v3.0 (and the following ICDR releases v3.1, v3.2, etc), the scaling level is defined by normalizing a set of reference instruments, in such a way that their average scale factor is equal to 1. These reference instruments are indicated with a (*) in Table 1-2.
For the ICDR, a regular download of new TSI data is performed for the active instruments before launching the ICDR processing. Currently these active instruments are: DIARAD/VIRGO, PMO6/VIRGO and TIM/TSIS. This list is likely to change in the future due to probable discontinuation of the SOHO satellite (with DIARAD and PMO06 instruments onboard) and also the incorporation of new instruments like DARA and CLARA.
The general characteristics of this Climate Data Record (CDR) are summarized in Table 1-1.
Table 1-1: General characteristics of the C3S v3.x daily TSI CDR.
C3S daily TSI timeseries | |
Spatial resolution | NA |
Grid | NA |
Temporal resolution | Daily mean |
Time period | CDR : 1st Jan. 1979 to 31st Dec. 2020 ICDR : 1st Jan. 2021 to present (~ 10 days latency) |
Format | ASCII |
Reference level for the fluxes | Irradiance at 1 Astronomical Unit (AU) + Irradiance at actual Earth-Sun distance |
Table 1-2: Total Solar Irradiance space instruments (the acronyms are defined in footnote). The instruments used in the C3S v3.x composite are indicated in bold while the 5 instruments used to define the absolute level are marked with (*).
Instrument1 | Platform(s) | Used | Operation period(s) | References |
TCFM | Mariner-6 & 7 | No | 1969 | |
ERB | Nimbus 6 | No | 1975 | |
Nimbus 7 | Yes | 1978 - 1993 | ||
ACRIM 1 | SMM | Yes | 1980 - 1989 | |
Solcon 1 | Spacelab 1 | No | 1983 | |
ERBE | ERBS | Yes | 1984 - 2003 | |
NOAA-9 | Yes | 1985 - 1989 | ||
ACRIM 2 | UARS | Yes | 1991 - 2001 | |
Solcon 2 | Atlas 1 | No | 1992 | |
Sova 1 | Eureca | No | 1992 - 1993 | |
Sova 2 | Eureca | No | 1992 - 1993 | |
ISP-2 | Meteor-3 7 | No | 1994 | |
DIARAD/VIRGO | SOHO | Yes | 1996 - present | |
PMO06V-A/VIRGO (*) | SOHO | Yes | 1996 - present | |
ACRIM 3 | ACRIMSAT | Yes | 2000 - 2014 | |
TIM (*) | SORCE | Yes | 2003 - 2020 | |
DIARAD/SOVIM | ISS | No | 2008 | |
SIM | FY 3A | No | 2008 - 2015 | |
SOVA | Picard | Yes | 2010 - 2014 | |
PREMOS (*) | Picard | Yes | 2010 - 2014 | |
SIM | FY 3B | No | 2011 - present | |
TIM (*) | TCTE | Yes | 2013 - present | |
SIM | FY 3C | No | 2013 - present | |
TIM (*) | TSIS-1 | Yes | 2018 - present | |
CLARA | NorSat | No | 2018 - present | |
DARA | PROBA-3 | No | To be launched |
Figure 1 illustrates the TSI daily timeseries. The daily values are shown in grey while the red curve shows the 121-days running mean. The CDR (indicated as TCDR on the graph) starts during the solar cycle 21 and stops just before the increase of solar activity during cycle 25. The ICDR (interim) period is shown.
Figure 1-1: Illustration of the C3S daily TSI CDR (v3.0) and ICDR period (1/1/2021 onward), in grey. The 121-days running mean is also shown (orange curve).
1.2 Target requirements
The target requirements for the TSI daily records are discussed in the Target Requirements and Gap Analysis Document (TRGAD)[D5] and are summarized in Table 1-3. The stability requirement is slightly relaxed for the ICDR version. These requirements are verified in the Product Quality Assurance Report (PQAR, [D5]).
Table 1-3: Target requirements for the C3S v3.x daily TSI CDR.
Target requirements | |
Spatial resolution | NA |
Temporal coverage | 1st January 1979 - present |
Accuracy | TCDR : < 1 W/m² |
Stability | TCDR : < 0.3 W/m²/decade |
1.3 Data Format
The data comes as a simple ASCII text file that can be opened with many tools such as text editors (e.g. vi, gedit, notepad, etc.), spreadsheets (e.g. excel), and graphical tools (e.g. gnuplot). It contains a header followed by the actual data. The header provides information about the CDR such as the version, type (CDR or ICDR), creation date and time, license, documentation, input time series (instruments) that have been used, and scaling factors. Any user of the data should have a careful look at the header. The data part is organized per line, with 1 line per day, with 23 columns with the content specified in Table 1-4.
Table 1-4: Data format per column of the C3S v3.x daily TSI CDR.
col | Column content |
1 | Date expressed as fractional year (e.g. 1987.0 is 1st Jan 1987 at 00:00 UTC). This field is useful for visualization. |
2 | Total Solar Irradiance (TSI) value in W/m² at 1 Astronomical Unit (AU). This value is the daily mean. |
3 | Date expressed as Julian Day number (integer number). |
4 | Date expressed as a character string YYYYMMDD (YYYY=year, MM=month, DD=day) |
5 | Number of individual TSI values combined in the composite TSI for this day. |
6 | Estimated TSI uncertainty in W/m². |
7 | Earth-Sun distance in Astronomical Unit (AU) for this date at 12:00 UTC. |
8 | TSI value at the actual Earth-Sun distance, in W/m². |
9 | Flags for the instruments/models used in the composite. |
10 | Original TSI values for instrument ERB/NIMBUS7 |
11 | Original TSI values for instrument ACRIM1 |
12 | Original TSI values for instrument ERBS |
13 | Original TSI values for instrument ACRIM2 |
14 | Original TSI values for instrument DIARAD/VIRGO |
15 | Original TSI values for instrument PMO06/VIRGO |
16 | Original TSI values for instrument ACRIM3 |
17 | Original TSI values for instrument TIM/SORCE |
18 | Original TSI values for instrument PREMOS |
19 | Original TSI values for instrument SOVAP |
20 | Original TSI values for instrument TIM/TCTE |
21 | Original TSI values for instrument TIM/TSIS1 |
22 | Original TSI values for model SATIRE |
23 | Original TSI values for model NRLTSI2 |
The 9th column provides a character string composed of 14 digits, one for each instrument/model used in the composite. The order of these digits follows the order in the table. The meaning of each digit is presented in table 1-5. As an example, the character string “02030000000011” means that only instruments 2 and 4 are used for the daily mean for this particular day.
Table 1-5: Instrument flag code.
Instrument flag code | |
---|---|
0 | No data available for this day. The value in the instrument column is “NaN”. |
1 | Data available for this day, but not used in the composite. The non-used value is in the instrument column. |
2 | Data available for this day and used in the composite. The non-used value is in the instrument column. |
3 | Data are not available for this day but interpolation is done. The interpolated value is given in the instrument’s column. |
4 | Data rejected for this day (e.g. outlier), interpolation is done. The original value is given in the instrument’s column. |
The following figure 1-2 shows the beginning of the C3S TSI data file. The two last columns provide the TSI value from the SATIRE-S (Ball et al., 2014) and the NRL TSI v2 semi-empirical models. These models are not used in the CDR, except SATIRE-S at the very beginning of the record (between 1st January 1979 and 6 November 1980).
Figure 1-2: Beginning of the C3S TSI data file.
The users are invited to read the ATBD [D1], the PQAD [D2], the PQAR [D3], the SQAD [D4] and the TRGAD [D5] documents for additional information on the data product and production system.
1.4 Disclaimer and License
This data product has been produced by the Royal Meteorological Institute of Belgium (RMIB), on behalf of the Copernicus Climate Change Service (C3S). The following License and disclaimer apply: https://cds.climate.copernicus.eu/api/v2/terms/static/licence-to-use-copernicus-products.pdf
2. Data access information
2.1 Data access through the RMIB
The C3S daily Total Solar Irradiance (TSI) timeseries is made available to the C3S Climate Data Store (CDS) through an HTTPS server hosted by the Royal Meteorological Institute of Belgium (RMIB). The server provides a validated version of the CDR over the period: 1st January 1979 – 31st December 2020 (in version 3.0):
https://gerb.oma.be/tsi/C3S_RMIB_daily_TSI_composite_TCDR_v3.0.txt
and regularly updated the ICDR with increasing version number v3.x, e.g.:
https://gerb.oma.be/tsi/C3S_RMIB_daily_TSI_composite_ICDR_v3.1.txt
In addition, a daily update of the ICDR is performed in the “latest” file:
https://gerb.oma.be/tsi/C3S_RMIB_daily_TSI_composite_ICDR_v3_latest.txt
2.2 Data access through the CDS
Data access through the CDS
Within C3S, the distribution will be through the CDS (https://cds.climate.copernicus.eu/) where documentation created for the inclusion of the data in the CDS, such as this PUGS, will be also provided.
2.3 Product ordering process
You need to be registered and logged in to order products in the CDS. A login is provided upon registration, all products in the CDS are delivered free of charge.
References
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