GC42A-01 INVITED
Total Irradiance Monitor Observations of Total Solar Irradiance
The Total Irradiance Monitor (TIM) is the most recent instrument launched to measure total solar irradiance (TSI) from space. This electrical substitution radiometer has on-orbit degradation tracking to provide very stable long- term measurements of the net solar radiation incident on the Earth, and the instrument continues the 29-year record of this natural driver of Earth climate. Currently flying on the SOlar Radiation and Climate Experiment (SORCE), the TIM has been providing stable, low-noise, and accurate measurements of TSI since early 2003. The TIM will next be flying on NASA's Glory climate mission and is one instrument of the Total Solar Irradiance Sensor (TSIS) selected to continue this important climate record well into the future. The SORCE/TIM has created renewed interest in the TSI absolute value and has acquired the first measurements of the total radiant energy released by large solar flares. Improvements in ground-based calibrations starting with the Glory/TIM will establish traceability linking current to upcoming measurements, solidifying the existing TSI climate data record in the undesirable event of a future data gap. http://lasp.colorado.edu/sorce
GC42A-02 INVITED
Measurement of the Total Solar Irradiance over cycle 23: results from DIARAD/VIRGO.
The Total Solar Irradiance (TSI) is measured from space since 29 years, covering 2.6 11 year solar cycles. Over the last 12 years, covering solar cycle 23, TSI measurements are available from the VIRGO experiment on the SOHO satellite. SOHO is located at the L1 Lagrange point, offering continuous sun observation and a stable thermal environment. VIRGO contains two independent radiometers, DIARAD and PMO, each with their own ageing monitoring capabilities. From these two radiometers, DIARAD is the only one with a nominal operation over the entire mission, and DIARAD has the lowest ageing. We present the ageing correction of DIARAD and PMO by the DIARAD team, and discuss the differences with the versions available from the PMO team. In addition to the normal exposure dependent ageing corrections applied by both the DIARAD and PMO teams, the PMO team applies additional 'exposure independent corrections' or 'sensitivity changes' which create an artificial downward trend of about 0.4 W/m2 for both DIARAD and PMO. Besides the two independent measurements of the TSI variation over cycle 23 from DIARAD and PMO, two more independent measurements over the complete cycle are available, on the one hand from a combination of ACRIM 2 and ACRIM 3, on the other hand from a combination of ERBS and TIM. All together, these measurements allow to measure the decadal trend of the TSI variation over cycle 23 with an unprecedented accuracy. All instruments show a similar long term behaviour except ACRIM 3 which shows a faster decline. We construct a composite time series using DIARAD/VIRGO as a reference instrument to put all instruments at the same absolute level. From the composite time series we can conclude there is no significant decadal trend during cycle 23. This is in contradiction with the ACRIM composite which shows a decreasing trend due to the ACRIM 3 decline, and with the PMO composite which shows a decreasing trend due to the 'exposure independent corrections' applied to the VIRGO radiometers.
GC42A-03 INVITED
The Total Solar Irradiance Record and Its Continuity
Continuous time series of total solar irradiance (TSI) observations have been constructed from the set of redundant, overlapping TSI measurements made by satellite experiments during the past 29 Years. One, the ACRIM composite [Willson & Mordvinov, 2003], displays a significant upward trend in TSI of 0.04 percent per decade during solar cycles 21-23. Another, the PMOD composite [Frohlich & Lean, 1998], displays no significant trend using different combinations of TSI data sets, computational philosophy and assumptions. The potential significance of solar variability as a climate forcing makes it important to determine which TSI composites best represents the measurement database. Two types of experiments have provided TSI satellite data: self-calibrating, precision TSI monitors and Earth radiation budget (ERB) experiments. TSI monitors provide much higher accuracy and precision and are capable of self-calibrating the degradation of their sensors, providing enhanced data traceability. The ERB experiments are designed to provide less accurate and precise TSI ‘boundary value' results for ERB modeling and cannot self-calibrate sensor degradation. The optimum composite TSI time series utilizes TSI monitor results where available. However, a two year gap in the TSI monitoring record between the ACRIM1 and ACRIM2 experiments (1989 - 1991) would have prevented compilation of a continuous record over the 29 years of satellite observations were it not for the availability of ERB results during the gap. The relationship between ACRIM1 and ACRIM2 results across the ACRIM gap can be derived using the overlapping ERB data sets: the Nimbus7/ERB and/or the ERBS/ERBE. These two choices are embodied in the construction of ACRIM and PMOD composites, respectively. The ACRIM composite uses the results for its constituent databases published by the experiment science teams and relates ACRIM1 and ACRIM2 using overlapping Nimbus7/ERB comparisons. The PMOD composite uses a different subset of the satellite TSI database, the ERBS/ERBE ACRIM gap ratio and modifies published Nimbus7/ERB and ACRIM1 results to conform its time series to the predictions of TSI proxy models. There are a number of differences between the ACRIM and PMOD composites but the most important is the trend during solar cycles 21 - 23. The absence of a trend in the PMOD composite has been shown to be an artifact of uncorrected degradation of ERBE results during the gap. The ERBS/ERBE database was significantly affected by uncorrected degradation throughout its observational lifetime and provides a less precise ACRIM gap ratio than the Nimbus7/ERB results. TSI proxy models are not competitive in precision or accuracy with satellite observations. Their use in constructing the PMOD composite convolutes the relatively high uncertainty of the model with the observational data and is therefore less likely to represent the extant TSI observational database with the greatest fidelity. Modifications of TSI results by PMOD obfuscates the relationships between the original observations' SI calibrations and traceabilities and the composite's representation of the TSI time series. The ACRIM TSI composite's use of original results from satellite experiment science teams likely provides the most accurate representation of the extant TSI satellite measurement database and therefore, of TSI variability knowledge. The TSI record has been sustained by overlapping, redundant experiments using their level of measurement precision to sustain longer term traceability. This TSI monitoring strategy is essential for continuity in the future because the uncertainty of current satellite sensors (~ 0.1 %) is an order of magnitude too large to detect subtle long term TSI variations of potential climate change significance. http://www.acrim.com
GC42A-04 INVITED
The phenomenological solar effect on climate
We discuss several secular solar proxy reconstructions and investigate the secular solar influence on climate under different northern hemisphere temperature and solar data scenarios using a phenomenological energy balance model. The model is constrained in such a way as to reproduce the phenomenological 11-year solar-induced global surface temperature cycle which presents a peak-to-trough amplitude of approximately 0.1K [IPCC 2007, p. 674]. We show that during the 20th century the sun might have contributed from a minimum of 31±8% to a maximum of 52±21% of the warming and that the climate had a significant preindustrial variability since the little ice age. Estimates of the solar contribution to climate change are found to be even greater by adopting ACRIM TSI satellite composite since 1980.
GC42A-05 INVITED
Some Issues of Solar Irradiance Variability and Climatic Responses: A Brief Review
In this paper, I will overview the difficulties surrounding a physical understanding of solar irradiance variability to contrast the superficial results from parametric fitting procedures. Related problems and consequences will be discussed. I will also offer some thoughts and empirical evidence for solar climatic responses on a range of spatial and temporal scales.
GC42A-06 INVITED
Climate Response to Solar Forcing
Most Energy-Balance Models (EBM) tend to underestimate terrestial surface response to solar variability, as evidenced by their much smaller surface warming in response to the 11-year solar cycle, whose variability in radiation has been accurately measured by satellites and the earth's global response deduced from instrumental records by Camp and Tung[2007] recently. In this talk we review both observational and modeling studies, including the solar radiative forcing of the lower atmosphere, the expected periodic and equililibrium responses, and why models in the past have not been able to adequately simulate them.