The Effects of Solar Variability on Earth's Climate A Workshop Report (2012) / Chapter Skim
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2 Workshop Presentations
2 Workshop Presentations
Pages 9-27
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From page 9... ...
The most rapid advances in this area are coming from simulations of magneto-convection on small scales in relatively shallow layers.4,5 Their extension to the much deeper layers of the convective and tachocline zones that are most likely to generate the 11-year sunspot cycle is not yet possible with today's computing power. At the September 2011 workshop, presentations on this topic included discussions of advances in solar radiometry, an assessment of solar influences on Earth's climate change, heliospheric phenomena responsible for cosmic ray modulation, and the behavior of quiet Sun contributions to solar irradiance on timescales ranging from years to thousands of years.
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From page 10... ...
Kopp and J.L. Lean, A new, lower value of total solar irradiance: Evidence and climate significance, Geophysical Research Letters 38:L01706, 2011; Copyright 2011 American Geophysical Union, reproduced by permission of American Geophysical Union.
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From page 11... ...
Kopp used an estimate of how the Sun might have varied coming out of the Maunder Minimum, by approximately 0.1 percent over 80 years, to derive accuracy and stability requirements for measuring TSI. Although change of that magnitude may be easy to measure over a solar rotation or over a maximum-to-minimum half solar cycle, it is a considerable challenge to derive a change that small over a century.
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From page 12... ...
The main aim of Peter Foukal's presentation was to consider whether the Sun dimmed enough during the 17th century Maunder Minimum of solar activity to influence climate. He argued that the simplest way to achieve sufficient dimming is through a decline in the area coverage of small flux tubes in the quiet magnetic network and internetwork (Figure 2.2)
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From page 13... ...
FIGURE 2.3 Variation in total solar irradiance (TSI) measured radiometrically (Physikalisch-Meteorologisches Observatorium Davos composite)
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From page 14... ...
This anti-correlation is the basis for using 14C and 10Be deposited in tree rings and ice cores as a proxy measure of solar activity dating back thousands of years. In addition to the 11-year GCR cycle, there is also a 22-year variation related to the polarity of the solar magnetic field.
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From page 15... ...
Such isotopic evidence currently provides the best chance of determining how much the solar magnetic field decreased during that period and therefore how much the Sun dimmed. He discussed how the differences between galactic cosmic rays and anomalous cosmic rays (ACRs)
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From page 16... ...
Muscheler continued by explaining how 10Be is produced in the stratosphere, becomes attached to aerosols, and is then sensitive to stratosphere-troposphere exchange processes before being deposited and trapped in ice cores. 10Be is further complicated by the geomagnetic field configuration characteristic of the location.
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From page 17... ...
Muscheler pointed out that there is good agreement between 10Be and 14C on the scale of the 11-, 88-, and 207-year solar cycles and that those signals can be clearly seen. On the other hand, there is no evidence of sustained periods on the order of 1,000 years of low solar activity in either the 10Be or the 14C record.
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From page 18... ...
Detection of the Solar Signal in Climate from Paleorecords Raymond S Bradley, University of Massachusetts Paleoclimate archives also provide an index of past solar activity, through the record of changes in cosmogenic isotopes recorded in tree rings and ice cores.
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From page 19... ...
Bradley suggested that further studies could be designed to address this question in a more rigorous and systematic manner. Detecting the Solar Cycle Via Temperature Proxies Back to the Maunder Minimum Gerald R
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From page 20... ...
This analysis suggests that >90 percent of the variance in temperatures can be accounted for by non-solar forcing factors and internal modes of variability. Using the central England temperature record to help define AMO cycles in earlier centuries, Tung also estimated that roughly half of the warming at the end of the Maunder Minimum period could be due to AMO variability and that, more generally, internal variability combined with volcanic forcing can explain a significant part of the variability commonly attributed to solar variations.
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From page 21... ...
. This transient behavior can be demonstrated using a simple two-box model of the mixed layer and deep ocean, and it applies to all radiative forcings, such as to the Mount Pinatubo volcanic aerosols, as well as for the response to the 11-year solar cycle.
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From page 22... ...
currently do not reproduce the tropical features seen in proxy records, giving instead a more uniform warming. One model was able to present an improved spatial structure of response to medieval solar forcing when the solar flux into the Indian Ocean was artificially enhanced, producing a small expansion of the zonal overturning circulation of the atmosphere over the tropical Pacific Ocean (Walker cell)
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From page 23... ...
Meehl, National Center for Atmospheric Research Gerald Meehl showed evidence that when observed sea surface temperature data are composited using only sunspot peak years, the tropical Pacific shows a pronounced La Niña-like pattern, with a cooling of almost 1°C in the equatorial eastern Pacific. This result has been seen in simulations using global coupled climate models.
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From page 24... ...
Both sets of panels show a weakening and poleward shift in the westerly jet. This figure does not present a model simulation of solar effects but demonstrates that a thermal perturbation to the stratosphere can produce similar patterns in tropospheric response, giving indications as to potential mechanisms for a solar influence on climate.
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From page 25... ...
Sassi, and H van Loon, Amplifying the Pacific climate system response to a small 11 year solar cycle forcing, Science 325:1114-1118, 2009; reprinted with permission from AAAS.
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From page 26... ...
, resulting in annually averaged variations in polar ozone of less than 0.06 percent. FIGURE 2.9 The atmospheric structure with incoming galactic cosmic rays and solar protons.
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From page 27... ...
International Satellite Cloud Climatology Project cloud analysis has suggested a 2 percent absolute change in cloud amount over the solar cycle, which corresponds to a 6 percent relative change.30 Although there is a 5-20 percent change in GCR-induced ionization in the troposphere over the solar cycle, this results (due to a number of dampening factors) in a smaller increase in nucleation rates, an even smaller increase in cloud condensation nuclei, and finally, a still smaller change in cloud amount.
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