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response is therefore most consistent with a bottom-up mechanism for driving the tropical lower
stratospheric response. A simplified analytic model suggests that much of the observed tropical lower
stratospheric response, including the solar cycle variation of total ozone, can be explained by this
However, these results are preliminary, and more work is needed to establish the relative
importance of the bottom-up and top-down mechanisms for producing the lower stratospheric response.
More detailed comparisons with global climate model simulations with and without a coupled
troposphere and ocean, with and without a simulated QBO, with TSI changes alone, and with various
possible solar spectral irradiance changes would assist in identifying the dominant physical mechanisms.
Amplifying the Pacific Climate System Response to a Small 11-Year Solar Cycle Forcing
Gerald A. Meehl, Julie M. Arblaster, Katja Matthes, Fabrizio Sassi, and Harry van Loon,
National Center for Atmospheric Research
One of the mysteries regarding Earth's climate system response to variations in solar output is
how the relatively small fluctuations of the 11-year solar cycle can produce the magnitude of the observed
climate signals in the tropical Pacific associated with such solar fluctuations. These observations include,
for peaks in the 11-year sunspot cycle, below-normal sea surface temperatures in the equatorial eastern
Pacific, enhanced precipitation in the Pacific ITCZ and SPCZ, and above-normal sea level pressure in the
midlatitude North and South Pacific. To investigate what could be producing these signals in
observations, two mechanisms, the top-down stratospheric response of ozone to fluctuations of shortwave
solar forcing, and the bottom-up coupled ocean-atmosphere surface response, are included in versions of
three global climate models with either mechanism acting alone or both together. We show that the two
mechanisms act together to enhance the climatological off-equatorial tropical precipitation maxima in the
Pacific, lower the eastern equatorial Pacific sea surface temperatures during peaks in the 11-year solar
cycle, and reduce low-latitude clouds to amplify the solar forcing at the surface.
Detection of the Solar Signal in Climate from Paleorecords
Raymond S. Bradley, Climate System Research Center, University of Massachusetts
All paleoclimatic studies of solar forcing rely on the record of 14 C or 10 Be anomalies from tree
rings or ice cores as a proxy for changes in irradiance, even though the relationship between variations in
these cosmogenic isotopes and total (or UV) solar irradiance remains enigmatic. Furthermore, the record
of anomalies that is generally used is derived by first removing the (large) geomagnetic signal in some
way, adding uncertainty to the resulting anomaly series. But this is generally the starting point for
paleoclimatic studies that involve solar forcing. Although many paleoclimate studies claim that there is a
record of solar forcing in proxy records, very few of these demonstrate a convincing, statistically
significant relationship. Often, the argument rests on nothing more than a crude similarity between a time
series of the proxy and the cosmogenic isotope anomaly series. In other cases, the claim may be based on
spectral power in the proxy record at the approximate frequencies known to be present in the cosmogenic
isotope series. Proxies may be temperature-related, or hydrological indicators. In short, although there is
a lot of literature on this topic, very little of it stands up to scrutiny. Nevertheless, rather surprisingly, if
the individual series (with their inherent limitations) are accepted, and the implied relationships are
mapped out, a fairly coherent pattern emerges, providing an intriguing hint that some of the recognized
climate changes during the Holocene may indeed have been driven by solar activity changes. Notably,
periods of low solar activity are generally associated with lower temperatures at mid- to high-latitude
sites, and with weaker monsoon activity in the tropics. However, most published paleoclimate studies do
not recognize any link with solar forcing, and so there is a danger of the “reinforcement syndrome,”
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