SH41A-01
Secular variations of solar activity and irradiance
Regular direct measurements of solar activity started around 1611 when sunspots detected by telescopic means began to be counted. Solar irradiance variations have been recorded for a much shorter time, only since 1978. Clearly, there is a need to extend both of these records into the past. In this talk reconstructions of solar irradiance back to the Maunder minimum and of sunspot number over multiple millenia are introduced. A comparison with climate reconstructions over the last millenium is shown and the next necessary steps in this line of research are considered.
SH41A-02 INVITED
A Critical Review of the Time Series of Total Solar Irradiance Satellite Observations
Continuous time series of total solar irradiance (TSI) observations have been constructed from the set of contiguous, redundant, overlapping total solar irradiance (TSI) measurements made by satellite experiments during the past 28 years. One, the ACRIM composite time series [Willson & Mordvinov, 2003], detects a significant upward trend in TSI of 0.04 percent per decade during solar cycles 21-23. Another, the PMOD composite [Frohlich & Lean, 1998], detects no significant trend using different combinations of TSI data sets, computational philosophy and assumptions. The potential significance of the ACRIM upward trend as a climate forcing makes it important to explore the trend difference to determine which of the two composite TSI time series best represents the measurement database. Two types of experiments have provided TSI 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. The ERB experiments are designed to provide less accurate and precise TSI �boundary value' results for ERB modeling and cannot self-calibrate sensor degradation. While the optimum composite TSI time series utilizes TSI monitor results to the maximum extent possible, 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 28 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 philosophy of the ACRIM composite is to use the unaltered results published by the experiment science teams and the Nimbus7/ERB ACRIM gap ratio. The PMOD composite approach uses a different subset of the satellite TSI database, the ERBS/ERBE ACRIM gap ratio and modifies published Nimbus7/ERB and ACRIM1 results, based on degradation assumptions derived from linear regression 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 and any composite based on the ERBS/ERBE ACRIM gap ratio 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 even the lowest quality satellite TSI observations. Their use in constructing the PMOD composite convolutes the relatively high uncertainty of the model with the observational data and is less likely to represent the best interpretation of the extant TSI observational database. The PMOD composite used modified published Nimbus7/ERB and ACRIM1 data. The ACRIM1 modifications were based on erroneous assumptions regarding degradation of the experiment. No effort was made to verify these assumptions using actual ACRIM1 data. The resulting PMOD composite provides better agreement with TSI proxy model predictions during the maximum of solar cycle 21 but does not provide the best representation of the actual TSI. The ACRIM TSI composite time series is the most accurate representation of the extant TSI satellite measurement database. It doesn't rely on imprecise proxy modeling or modifications of published observational results.
http://www.acrim.com
SH41A-03 INVITED
Surface Temperature Reconstructions for the Last 1000 Years
This is a presentation of results from a recently released report written by a committee established by the National Research Council and chaired by the speaker. The report was titled the same as the title of this talk. It focused on the methods of reconstructing the large scales of such surface temperature fields, since there has been considerable discussion in the scientific literature, assessments such as the IPCC, the popular press, blogs and even Congressional Hearings. The so-called �hockey stick' curve indicating a gradual cooling from the beginning of the record at about 1000AD to roughly 150 years ago when the curve take a steep upward trend (the so-called global warming). The original publications by Mann, Bradley and Hughes were careful to present and emphasize error margins that have been ignored by many in the controversy. The Committee found that numerous subsequent publications have reported reconstructions that utilized different data and different statistical assumptions. These all fall within the error margins of the original studies. While the committee has some reservations about the period prior to the year 1600AD, it still concludes that it is plausible that surface temperatures averaged over the Northern Hemisphere over the last three decades are plausibly the warmest for any such comparable period in the last 1000 years.
SH41A-04 INVITED
A phenomenological reconstruction of the solar signature in the NH surface temperature records since 1600.
Herein we use a phenomenological radiative relaxation model for reconstructing the solar signature on 400 years of two Northern Hemisphere global surface temperature records since 1600, under several hypotheses. The model, which depends on only two parameters, is calibrated using the solar and temperature data covering the pre-industrial era (roughly 1600-1900), when negligible amount of anthropogenic-added climate forcing was present and the sun realistically was the only climate force affecting climate on a secular scale. Then, we adopt the calibrated model to estimate the relative contribution of the (solar-induced) natural versus anthropogenic-added climate forcing during the industrial era (roughly since 1900). We use two recent secular Northern Hemisphere proxy temperature reconstructions, one with a minimal [\emph{Mann and Jones}, 2003] pre-industrial secular variability and the other with a greater [\emph{Moberg et al.}, 2005] secular variability from 1600 to 1849, and the Northern Hemisphere instrumental surface temperature reconstruction since 1850 [\emph{Brohan et al.}, 2006]. We also use two total solar irradiance (TSI) proxy reconstructions, one with a minimal [\emph{Wang et al.}, 2005] and the other with a greater [\emph{Lean}, 2000] secular variability, and two TSI satellite composites [\emph{Fr\"ohlich and Lean}, 1998; \emph{Willson and Mordvinov}, 2003] since 1980. We find that the relative contribution of the (solar-induced) natural versus anthropogenic-added climate forcing during the last century depends on the particular temperature secular proxy reconstruction adopted. By adopting the `hockey stick' reconstruction by \emph{Mann and Jones} [2003] the solar contribution to the warming since 1900 would be minimal. According to the most recent temperature and TSI reconstruction by \emph{Moberg et al.} [2005] and \emph{Wang et al.} [2005], we find a good correspondence between global temperature and solar induced temperature signals during the pre-industrial period such as the cooling periods occurring during the Maunder Minimum (1645-1715) and the Dalton Minimum (1795-1825). The sun might have contributed 50% (or more if ACRIM is adopted) of the observed global warming since 1900.
SH41A-05
A Comparison of Sunspot Photometric Indices From Ground-Based Data and MDI/SOHO
Comparing ground-based and space-based sunspot photometric indices is useful in extending the time series for studying variatons in total solar irradiance (TSI). Photometric sunspot indices from CFDT2 images obtained at the San Fernando Observatory have been compared with those from images obtained by MDI/SOHO and the Mauna Loa PSPT. We find very high correlations between them (R greater than about 0.99 for most). However, sunspot darkness is overestimated using MDI images by between 10 to 20 %. A composite sunspot deficit created from red and blue SFO/CFDT2 images correlates well (R =.99, n=53) with deficits from PSPT red images. This work has been partially supported by grants from NASA (NAG5-12905) and the NSF (ATM-0533511).
http://www.csun.edu/sfo
SH41A-06
Tropospheric Adjustment: the Responses of Temperature and Precipitation to a Change in Solar Forcing
The responses of the HadCM3 and NCAR CCM3 general circulation models to a change in solar insolation are compared to their responses to a doubling of atmospheric CO$_2$ concentration. In both models, it is found that the important difference is the rapid adjustment of the troposphere in the solar case that reduces the value of effective forcing by about 25%. Clear-sky warming appears to make the major contribution. Subsequent evolution of the coupled troposphere, land surface, ocean mixed-layer system proceeds with a very similar sensitivity and surface temperature response pattern to that under a CO$_2$ forcing of the reduced value. Previous work has established that modeled precipitation responds more strongly to solar and volcanic forcing than to greenhouse gas forcing per unit temperature, because of the direct effect of greenhouse gases on the troposphere. (The precipitation response to surface temperature independent of direct effects is the same in both cases.) Recently, it has been argued that this is the reason that solar and volcanic forcing dominate the observed 20th century precipitation record, while greenhouse gas forcing dominates the observed 20th century temperature record. In our models, the smaller temperature response to solar forcing causes the overall precipitation response per unit \emph{forcing} to be similar to or smaller than that to CO$_2$. Hence, it is possible that the relative importance of different forcings to 20th century temperature and precipitation is due to lower sensitivity of temperature to solar and volcanic forcing, rather than lower sensitivity of precipitation to greenhouse gas forcing.