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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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2
Plan Review

The NOAA Working Group Report (Appendix B) outlines the TCTE mission. This mission is the NOAA approach to address the impending gap in TSI measurements that is expected to occur with the imminent end of SORCE and the late 2016 to early 2017 launch of TSIS on the JPSS FF-1 mission. This approach evolved from two studies conducted by Greg Kopp and Judith Lean for NOAA.1 In its review of the TCTE proposal, the Committee considered the information contained in all three documents (the NOAA Working Group Report, Study A, and Study B). Studies A and B arose from the involvement of Kopp and Lean in a LASP/NRL/NIST team that successfully competed for a 3-year award from the NOAA Climate Data Record (CDR) Program in 2009. Following the GLORY launch failure, Kopp and Lean offered to conduct the two studies as part of their contribution to that project. The NOAA Working Group Report reviewed by the Committee was an abbreviated summary of these two reports plus a very brief description of the TCTE mission and even briefer description of the accommodation of the TIM on the STPsat-3. Much of the analysis that frames the rationale for TCTE concerned the impact of a gap in the TIM data record that started with the TIM launched on SORCE in 2003 (January 25). The NOAA data record as perceived, however, extends back to earlier satellite measurements as summarized below. The perspective of the impending gap on this longer record was not quantitatively addressed in the studies.

TOTAL SOLAR IRRADIANCE DATA RECORD

An approximate two-year gap occurred between ACRIM I and ACRIM II (see upper panel of Figure 2.1).2 This hiatus in the ACRIM data record offers an ideal test case to gain some understanding of the influence of a gap on the construction of a TSI climate data record. Over the past several years, different procedures have been developed by three different groups to address this issue and to construct a composite time series (see lower panels of Figure 2.1) using ERBE data or the Nimbus HF data (sometimes augmented by TSI models based on proxy data) to fill the gap. Clearly the details of how the data are combined matter. Comparison between the composites of the change of levels of irradiance during solar

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1 The two Kopp and Lean studies, Uncertainties Spanning Potential SORCE/TIM to JPSS/TIM Gap (2011) and The Solar Climate Data Record: Scientific Assessment of Strategies to Mitigate an Impending Gap in Total Solar Irradiance Observations between the NASA SORCE and NOAA TSIS Missions (2013), will be referred to as Study A and Study B, respectively. Both are provided in Appendix C.

2 ACRIM is the Active Cavity Radiometer Irradiance Monitor instrument and is part of NASA’s Earth Observing System program.

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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image

FIGURE 2.1 Upper Panel The daily averaged values of TSI from radiometers on different space platforms since November 1978: HF on Nimbus7, ACRIM I, ERBE, ACRIM II, VIRGO, ACRIM III, and TIM on SORCE. The data are plotted as published by the corresponding instrument teams. Lower Panels The PMOD, ACRIM and IRMB composite TSI as daily values plotted in different colors to indicate the data sources used in the composite. SOURCE: PMOD. (ACRIM is the Active Cavity Radiometer Irradiance Monitor, ERBE is the Earth Radiation Budget Experiment, VIRGO is the Variability of solar Irradiance and Gravity Oscillations).

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

TABLE 2.1 Climate Data Record Requirements for the JPSS/TIM. SOURCE: NOAA Working Group Report.

Parameter CDR Requirement
Absolute Accuracy 0.01% (100 ppm; 0.14 Wm-2)
Stability (long-term precision) 0.001%/yr (10 ppm/yr; 0.014 Wm-2/yr)
Noise (short-term precision) 0.001% (10 ppm; 0.014 Wm-2)

Note: 1 ppm ~ 0.0014 Wm-2

minimum periods can be taken as a measure of overall precision of the record. The differences between the three reconstructions alone are greater than the 10 ppm/yr precision specified in Table 2.1 and have resulted in considerable debate as to the Sun’s role in warming over the decade 1986 to 1996 and misinterpretation of the influence of the Sun on recent global warming.

Because the stringency of the CDR requirements (Table 2.1) severely limit solutions for filling a gap, the Committee determined that it was important to take a step back and revisit these CDR requirements themselves. The traceability of the TSI requirements appears to arise out of an understanding of the variability of the Sun rather than from an understanding of Earth climate system variability and change (Kopp, 2011). The climate-driven requirements first began to emerge in Solar Influences on Global Change (NRC, 1994) and can be traced through a series of documents (Box 2.1). Since then much more has been learned about the variability of Earth’s energy imbalance (Loeb et al., 2012) and about how to define requirements tailored for climate change detection (Wielicki et al., 2013). Box 2.2 later in this chapter revisits the TSI CDR requirements formulated within the context of this new understanding.

COMMITTEE FINDINGS AND CONCLUSIONS

Question 1: Does the plan appropriately reflect the scientific content of the commissioned papers?
Findings

1.      The Committee found that the plan faithfully followed the Kopp and Lean studies. The plan also displayed an admirable degree of nimbleness in reacting to a pressing need to fill an impending CDR gap. The solution presented was a creative, rapid, and low-cost response that exploited the availability of an existing engineering instrument model, and heritage in engineering, mission architecture, and data analysis. Studies A and B themselves also provide a useful analysis that furthers our understanding of the performance of existing space-borne TSI measurements.

Given published information on instrument accuracy and stability available as of the dates of the Kopp and Lean studies and the NOAA working group report, the Committee considers the review of gap-filling alternatives to be fair. While the plan did reflect the scientific content of Studies A

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

BOX 2.1
Traceability of Total Solar Irradiance Measurement Requirements

Requirements for climatically useful TSI measurements can be traced to discussions in Solar Influences on Global Change (NRC, 1994). The National Polar-Orbiting Operational Environmental Satellite System (NPOESS) Integrated Operational Requirements Document (IORD-I; NPOESS, 1996) specified threshold (minimum success) and objective (goal) accuracies of 0.1% and 0.035% and precisions of 0.002% yr-1 and 0.0005% yr-1, respectively. An NRC workshop (NRC, 2000) changed the accuracy objective to 0.01%, restated precision threshold and objective as 0.002% and 0.001% respectively, and added stability threshold and objective values of 0.002% yr-1 and 0.0005% yr-1, respectively. These values were formalized in IORD-II (NPOESS 2001). A multiagency workshop (Ohring, 2007) confirmed the accuracy objective of <0.01% and recommended a stability objective of <0.001% yr-1. A report by Datla et al. (2009) quoted the less stringent threshold values in IORD-I for accuracy and stability. Given the inconsistency of the values, transition from research to operational requirements, unclear justifications for the values, and the emergence of a Climate Data Record Project at NOAA, a workshop was held in 2011 to sort out these issues (LASP, 2011). When NPOESS was restructured in 2010, NOAA became responsible for JPSS. The original Level 1 requirements for the TSI-measuring part of the TSIS package selected to fly on JPSS-1 stated minimum success accuracy and stability of 0.35% and 0.035% yr-1 and goals of 0.01% and 0.001% yr-1, respectively (Viereck and Denig, 2011). The present Level 1 threshold requirement values are listed in Table 2.1; objective values are one-half of the values in Table 2.1 (Viereck and Denig, 2011). Justification for the values was originally driven by instrument capability but is now primarily based on present understanding of long-term solar variability and a need to detect <0.1% long-term TSI changes in a century (Kopp, 2011).

and B, as presented it lacked certain essential information needed to determine the strength of the proposal. No reliability information (probability of TCTE surviving until the launch of JPSS FF-1) for the key mission elements was provided. There was no budget and no clear timeline of the funding or continued support from the Air Force was offered. These aspects of the Committee’s review are discussed in greater detail in response to Question 2 below.

Question 2: Does the potential alternate method in the plan maintain the integrity of the data record?

Findings:

2.a   Study B clearly argues that the CDR requirements can only be met when data overlap occurs at both ends of the gap. Because no reliability estimates of mission components or information about mission funding or Air Force support were provided, it was not

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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         possible to assess the real likelihood of the gap being filled. The Committee concluded that the plan is unable to ensure the integrity of the data record because as presented it is a 1.5 year plan to fill a 3+ year gap.

2.b   The launch of TCTE is currently scheduled for October 30, 2013, which will likely ensure overlap with SORCE. Although not presented to the Committee, it appears the probability is high of SORCE operating beyond the launch of TCTE, thus providing critical overlap at the front end of the gap. This determination was based on information provided by the Spring 2013 SORCE senior review proposal made available to the Committee by NASA (Woods, 2013). A 1.5 year collection of data on orbit however leaves a gap of more than a year between the stated end of TCTE and beginning of the TSIS on JPSS FF-1.

2.c   Although the Committee was not briefed on what elements of the mission limit the lifetime of TCTE, it was able to determine that there is high probability that the single-string spacecraft could operate beyond 3 years. Independent information provided to the Committee by the spacecraft provider indicated that the single string baseline STPSat-3 type bus reliability for 3 years on-orbit is above 0.80 and drops to 0.75 for 4 years on orbit (personal communication to Committee Chair). Estimates provided to the Committee by LASP indicate that the TIM instrument reliability is 0.80 at 3 years and 0.74 at 4 years. Thus the likelihood of achieving 4 years of data on orbit and thus overlap with the JPSS/TSIS (scheduled to launch in late 2016 to early 2017) is 0.56, or slightly better than 50%. In the reliability data provided to the Committee by LASP, the drop in probability of TCTE survival from one to two years, two to three years, and three to four years are all the same: about 0.86 times the previous year’s value. This is typical of spacecraft and instrument reliability estimates. Thus, the Committee can estimate the probability of overlap if the launch of JPSS/TSIS is delayed beyond 2017. If the launch slips to 2018, the probability of overlap drops to 0.48. If it slips to 2019, the probability of overlap drops further to 0.41.3

2.d   The NOAA Working Group report did not provide information on funding support for the TCTE mission and stated that NOAA is working with the Air Force to ensure operation of the STPSat-3/TCTE mission for as long as possible. Continued funding and cooperation from the Air Force will be necessary for continued data collection and maintaining the integrity of the data record.

Question3: Does the plan adequately summarize the strengths and weaknesses of the proposed approach?

Finding:

3      Taken together, the three documents provided a balanced discussion of strengths and weakness of the proposed method to fill the TSI gap and

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3 The probability of TCTE maintaining data collection for four years is 0.56. The probability of survival drops by a factor of about 0.86 each year. Thus the probability of TCTE surviving five years (until 2018) is 0.56 X 0.86 = 0.48. The probability of TCTE surviving six years (until 2019) is 0.48 X 0.86 = 0.41.

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

         recognized fully the limitations of the proposed TCTE gap filler. In developing the plan, the analysis of the stability uncertainty estimates for ACRIM3, VIRGO, and PREMOS in comparison to SORCE/TIM was essential in the formulation of TCTE. The comparative stability of different instruments and empirical models summarized in Table 2.2 are based on comparisons of the instrument data records relative to those of the SORCE/TIM and from changes between each instrument’s successive data versions. The Committee was however aware that it was only being presented a TIM-based gap-filling concept and then only the TCTE concept. The Committee considered material from the NOAA Working Group Report, Kopp and Lean Studies A and B, the SORCE and ACRIM-3 NASA Senior Review proposals, existing literature on TSI observations, and past changes in TSI records needed to correct instrument artifacts. Overall, the arguments in favor of TIM as the current best reference were the most compelling. The TIM instruments for example show one-third the on-orbit degradation of that for ACRIM, and reduced systematic noise during quiet sun periods. The use of TIM as the reference leads directly to the results in Table 2.2 and Figure 2.2.

Figure 2.2 illustrates how the uncertainty in TSI introduced by the presence of a gap is influenced by a number of parameters. Based only on the absolute accuracy of the instruments, shown in Figure 2.2 as the dashed line at ~360 ppm representing the accuracy of SORCE/TIM, the uncertainty does not depend on gap length. With overlaps, provided by intervening measurements or models, the drift between the two TIM measurements can be estimated and the uncertainty reduced. Figure 2.2 illustrates how longer overlaps and shorter gaps enhance this effect; for example with a gap of 3 year duration an overlap of more than 0.5 years will improve uncertainty over that which would be obtained by relying on absolute accuracy alone. The improvement is limited for short (< ~10 days) overlaps by noise in the measurements. Figure 2.3 provides analogous illustrations of alternative gap-filling methods.

Because filling the TSI data gap with the TCTE is not assured, it was prudent to examine other options.4 In particular, models of TSI based on proxy data (e.g., sunspot darkening and facular brightening) can, in principle, be used to fill a gap depending on the demonstrated performance of the model, duration of the gap, and availability of high-quality proxy data. In Study B several models were constructed based on linear regression of various combinations of proxy data to the TIM TSI observations (2003-2012). The best agreement was an NRL model based on a sunspot blocking index derived from ground-based white light images and a Mg II spectral line ratio index derived from SORCE/SOLSTICE observations. This model had a correlation coefficient of 0.961 and thus fits 92.4% of the observed TSI measurement variance (Study B). The

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4 It is beyond this Committee’s charge to prioritize other options (e.g., proxy data models versus other space instruments). However, the Committee does note that NOAA would be wise to utilize all available data resources to fill the gap.

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

TABLE 2.2 Instrument and Model Performance Estimates. SOURCE: Kopp and Lean Study B.

Instrument Stated Accuracy (ppm) Stability (ppm/y:r) Noise (ppm)
SORCE/TIM 350 10 4
ACRIMSat/ACRIM3b 1000 71 34
SoHO/VIRGO 2500 29 28
PICARD/PREMOS 300 79 <52
JPSS/TCTE/TIM 350 10 50a
JPSS/TSIS/TIM 100 10 10
NRL Model -NA- 48 38
SFO Model -NA- 88 19

aEffective noise due to orbital sampling at times of high solar activity. Instrument noise is less than 10 ppm.

bThe ACRIM Senior Review Proposal (Willson, 2013) states that ACRIM3 results have demonstrated a traceability uncertainty of < 5 ppm/yr and that LASP/TRF calibration will result in accuracy improvement. If these performance improvements prove to be true, ACRIM could be a viable alternative for filling the data gap.

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FIGURE 2.2 General effects contributing to uncertainties in filling a TSI data gap. Stability uncertainties increase with gap duration, limiting accuracy; measurement noise limits the uncertainties at short gap durations. Longer overlap durations with prior (SORCE/TIM) and following (JPSS/TIM) instruments improve knowledge of stability of, and agreement with, intervening gap-filling instrument or model, decreasing uncertainties. SOURCE: NOAA Working Group Report. (This figure, with accompanying explanation is in Appendix B.)

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

image

FIGURE 2.3 Estimated uncertainties as a function of gap and overlap duration for gap-filling alternatives: ACRIM3 (top left), VIRGO (top right), PREMOS (bottom left), and NRL model (bottom right). In all four cases, longer gap durations and shorter overlap times increase uncertainties. SOURCE: Kopp and Lean Study A. (This figure, with accompanying explanation is in Appendix C.)

SOLSTICE data will not outlive data from TIM so models based on non-SORCE data are relevant. The best correlation reported in Study B for such a model was 0.942, which fits 88.7%5 of the TIM variance.

The Committee considered two published comparisons not included in Study B. Ball et al. (2011) compared TSI modeled with SATIRE-S (based on sunspot images and magnetic field measurements) with observed TIM data. For the period 2003-2009 they found a correlation of 0.984 (97% of variance fitted). Chapman et al. (2012), using a different set of ground-based proxy observations for the period 20032010, found a slightly smaller correlation of 0.974 (95% of variance fitted) with TIM data. These two empirical models have recently been compared with the PMOD composite TSI index. Ball et al. (2012) for the period 1996-2008 obtained a correlation

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5 This value was calculated by the committee. It is simply the square of the correlation coefficient reported in Study B. This value, the coefficient of determination, gives the percentage of the total variation that is explained by the model (Wackerly et al., 2008).

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

of 0.981 and Chapman et al. (2013) found 0.96 for 2003-2010.

It appears that by using different proxy data sources than those of Study B, the agreement between empirical models of TSI and observations may be improved so that >95% of the TSI variance can be fit with a model. Combining such models with the instrumental approaches suggested in the Working Group Report would greatly improve the chances of successfully bridging a TSI gap. However, as noted in Study B, there is no certainty that the sources of proxy data for the models will be available during the TSI gap. Declining funding, age, and looming closures threaten both ground- and space-based sources of synoptic solar observations. Nor are resources readily available to improve the quality of or add new sources of solar data useful for TSI modeling.

A hypothetical alternative method for future gap filling not explicitly discussed adequately by the plan is reliance on absolute accuracy. Now that LASP has the TSI Radiometric Calibration (TRF) facility whereby it can provide a reported pre-flight absolute calibration of the TIM instruments to about the 200 ppm to 300 ppm level (personal communication from G. Kopp to the Committee), it seems that not only the TSIS TIM, but also the TCTE TIM and all subsequent TIMs (assuming maintenance of the TRF scale), should be calibrateable to this level. The Committee notes that these results have not been peer reviewed, but if this uncertainty can in fact be achieved and could be improved in the future to 100 ppm, we could be more tolerant of gaps, because comparison of any pair of sufficiently long (to overcome short-term random effects) segments of non-overlapping data, each with absolute uncertainty at this level, would approach the CDR values required for detecting solar variability. The TCTE provides an early test of this. It will be the first TIM to fly that was calibrated against the TRF (the PREMOS-A active cavity radiometer instrument was calibrated to 280 ppm in 2010), and thereby potentially one of the most absolute accurate measurements of TSI to date. The comparison of the TCTE TIM TSI value with all the others will provide a highly accurate tie point, and will validate the SORCE TIM and PREMOS values. This provides additional incentive to fly the mission, even if it does not fill the gap.

Question 4: Do the background documents and plan together fully explore the implications of loss of, or changes in, measurement on the understanding of Earth’s climate system and processes?

Finding:

4      The Committee was not initially convinced that the requirements as posed (Table 2.1) represent requirements that were derived from those relevant to understanding climate change. The Committee’s research on the source of the requirements given suggests they derive from empirical knowledge of solar variability and instrumental capability and are less related to the energetics of the Earth system (Box 2.1). To determine the implications of these requirements on the understanding of the Earth’s climate system, the Committee considered two different pathways for setting these requirements based on climate sensitivity, rather than on solar variability or instrumental capability. These are summarized in Box 2.2.

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Box 2.2
TSI Accuracy Requirements for Understanding Anthropogenic Climate Change

Approach I: The analysis below is based on the arguments for the measurement requirements of the CLARREO mission (Wielicki et al., 2013) and revolves around certain assumptions of future climate change. Dangerous climate change is internationally agreed to be ~ 2 °C over the long term (Copenhagen Accord, 2009). Best current estimate of equilibrium (long term) climate sensitivity is approximately 3 °C for an anthropogenic forcing of ~ 4 Wm-2 associated with a nominal doubling of carbon dioxide (Andrews et al., 2012). Thus a 2 °C warming corresponds to a radiative forcing of roughly 2.7 Wm-2 [(2 °C/3 °C)*4 Wm-2]. Because separation of natural from anthropogenic radiative forcing is required for adequate scientific understanding of the Earth’s climate system and processes, long term radiative forcing due to changing TSI should be known to at least 10 percent of the level of dangerous climate change with 95 percent confidence (2σ) in order to clearly separate anthropogenic signal from natural variability (e.g. Wielicki et al., 2013).a This suggests a knowledge of TSI changes to levels that can cause less than or equal to 0.13 Wm-2 (1σ) in radiative forcing of the climate system. Changes in TSI relate to changes in climate radiative forcing by ΔF = 0.7 ΔS /4, where ΔS is the change in TSI. The factor of 4 is the ratio of the Earth’s cross-sectional area to its surface area and the factor of 0.7 is the global average solar absorption of Earth (1 - albedo). Or equivalently, ΔS = 5.7 ΔF. This implies that the long term change in TSI should be known to 5.7 * 0.13 = 0.74 Wm-2 or less. The time interval for this long term trend in TSI should be roughly that over which current anticipated anthropogenic radiative forcing would reach the 2 °C warming level. Climate model simulations of doubled CO2 radiative

Coincidentally, the outcome of the calculations made by the Committee agrees with the pre-defined requirements in Table 2.1. Hence, given that the plan and the background documents together made their recommendations based on these requirements, the Committee considers that these documents, to an appreciable extent, explored the implications of loss of, or changes in, TSI measurements on the understanding of Earth’s climate system and processes.

This Committee was charged to address how the loss of TSI data specifically would affect understanding of Earth’s climate because TSI, and its variations, play a fundamental role in determining global average temperature. However, there is increasing evidence that variations in solar ultraviolet (UV) radiation contribute to regional and seasonal climate (Gray et al., 2010). In fractional terms UV changes are much larger than those in TSI and these directly affect the temperature and composition of the stratosphere, where UV is predominantly absorbed. To fully appreciate the potential of the Sun in regional climate change it is therefore essential that measurements of spectrally-resolved radiance are maintained in parallel

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

forcing typically use a roughly 1 percent increase in CO2 per year for a 70 year doubling time (Cubasch et al., 2001). This suggests that the rough time scale for the 2 °C warming for our metric is then (2 °C/3 °C)*70 years or ~ 50 years. A long term trend in TSI to be discernable above anthropogenic climate forcing is then 0.74 Wm-2/50 years = 0.015 Wm-2/yr. Since TSI ~ 1361 Wm-2 (Kopp and Lean, 2011), then a 1000 ppm/yr (0.1 percent) trend is 1.4 Wm-2/yr, and the 0.015 Wm-2/yr trend corresponds to an 11 ppm/yr trend in TSI. This value of 11 ppm/yr is similar to the current JPSS requirement of 10 ppm/yr stability for TSI observations.

Another way to look at the above requirement is that the 50 year change in TSI should be uncertain to less than 0.75 Wm-2 (1σ) which is equivalent to ~500 ppm. For the JPSS 100 ppm absolute accuracy requirement (1σ), the absolute accuracy requirement is ~ 1/5th the total trend uncertainty desired over 50 years. This level of accuracy would also provide a climate record that is robust to data gaps, unlike our current record.

Approach II: A second approach for setting the requirement relevant to climate change studies is to place the TSI change within the context of the global net radiation. Current estimates of ocean heat storage indicate that the global net radiation is ~ 0.5 Wm-2 (Loeb et al., 2012). TSI is one component of global net radiation, and its absolute accuracy should be no worse than 10 percent of global net radiation (2σ), or 0.025 Wm-2 (1σ). Using the same relationship between TSI and radiative forcing of the Earth’s climate, this results in a TSI absolute accuracy requirement for global net radiation of (0.025)(5.7) = 0.15 Wm-2, or ~100 ppm (0.01 percent) in TSI. The JPSS requirement is 100 ppm for absolute accuracy and thus is consistent with a requirement based on energy imbalance and long term ocean heat storage.

a 2σ represents two standard deviations from the mean of a Gaussian normal distribution. Approximately 95% of the distribution is contained within two standard deviations of the mean. This is a commonly used confidence boundary in statistics (Wackerly et al., 2008).

with those of TSI.

The TSI CDR has two components. There is the shorter, but more accurate record of the TIM era with SORCE/TIM-level data quality. There is also the full (33+ year) space-based TSI measurement record. This longer record, although not of the quality of the TIM era record, is still important to preserve. The NOAA Working Group Report focused on the impending TSI gap that is to occur because of end of life of SORCE and the failure of the GLORY mission. Much of the working group report emphasized the importance of maintaining an unbroken record of TSI to inform ongoing debates regarding the potential role of solar variability in influencing Earth’s climate. Thus the focus was directed to the shorter, more accurate TIM era record and no real discussion of the full TSI CDR and its stewardship was offered. Although this existing satellite data record, dating back to 1978, currently fails to meet the stability requirements of Table 2.1, the Committee believes it is also important to maintain the stewardship of the entire record and place the current TIM era data and impending gaps within the context of the longer data record. NOAA’s plan does not ensure continuity for the TIM-era record, but is more likely to ensure continuity of the full 33 year record.

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

ADDITIONAL THOUGHTS

While the Committee was charged with evaluation of NOAA’s response to an impending gap in TSI observations for climate research, NOAA’s response and its appropriateness can only be understood in light of how it fits into the larger context of climate observations. Unlike for weather observations, there is no U.S. or international climate observing system. As a result, monitoring of climate change including TSI is a necessarily ad hoc, high risk, and loosely coordinated activity across the 13 U.S. agencies of the U.S. Global Change Research Program (USGCRP). The USGCRP has the responsibility for climate change research, but has no authority over agency actions, nor budget to deal with observing system issues like those that arose for TSI when the NASA Glory mission launch vehicle failed March 3, 2011. Glory was to be the end of NASA leading TSI observations from space, with the NOAA JPSS weather satellite system beginning the next set of observations in 2016. As a result of the launch failure, the solution that NOAA found was severely constrained by cost, schedule, and programmatic challenges. The TCTE solution is not optimal in a scientific sense given roughly 50 percent likelihood of successful overlapping observations in the best case scenario of an on-time JPSS FF-1 launch combined with an absence of any programmatic issues in NOAA and Air Force collaboration on extending the TCTE mission life from 2 to 4 years. Yet in the context of the lack of a climate observing system, the TCTE solution can be considered optimal within the constraints present. We should expect similar issues in the future with many of the approximately 50 essential climate variables. There have been some recent reports that show a recognition of this challenge, in particular the U.S. NSTC “National Strategy for Civil Earth Observations” (April, 2013), and the international “Strategy Towards an Architecture for Climate Monitoring from Space” (January, 2013). Development of a national and international climate observing system could be the long term solution to climate monitoring challenges like TSI.

Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×

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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
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Page 9
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 10
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 12
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 13
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 14
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 15
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 16
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 17
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 18
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 19
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 20
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 21
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 22
Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
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Suggested Citation:"2 Plan Review." National Research Council. 2013. Review of NOAA Working Group Report on Maintaining the Continuation of Long-term Satellite Total Solar Irradiance Observation. Washington, DC: The National Academies Press. doi: 10.17226/18371.
×
Page 24
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Solar irradiance is a vital source of energy input for the Earth's climate system and its variability has the potential to mitigate or exacerbate a human-created climate. Maintaining an unbroken record of Total Solar Irradiance (TSI) is critical in resolving ongoing debates regarding the potential role of solar variability in influencing Earth's climate. Space-borne instruments have acquired TSI data since 1978. Currently, the best calibrated and lowest noise source of TSI measurements is the Total Irradiance Monitor (TIM) onboard NASA's Solar Radiation and Climate Experiment (SORCE). These TIM-era data are of higher quality than the older data in the full record. Thus, the TSI climate data record (CDR) has two components. There is the shorter, but more accurate record of the TIM era and the full (33+ year) space-based TSI measurement record. Both are important and require preservation.

Review of NOAA Working Group Report on Maintaining the Continuation of Long-Term Satellite Total Irradiance Observations evaluates NOAA's plan for mitigating the loss of total solar irradiance measurements from space, given the likelihood of losing this capacity from instruments currently on the SORCE satellite in coming years and the short term/experimental nature of the currently identified method of filling the data gap. This report evaluates NOAA's plan for mitigating the gap in total solar irradiance data.

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