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promptly, if produced in the stratosphere, or subsequently, if produced in the lower thermosphere or
mesosphere and transported to the stratosphere. NO x enhancements due to auroral electrons, medium-
and high-energy electrons, relativistic electron precipitation events, and SPEs have been measured
and/or modeled for decades. Model predictions and measurements show that certain years have
significant wintertime meteorological events, which result in the transport of EPP-caused NO x
enhancements in the upper mesosphere and lower thermosphere to lower altitudes.
The NO x -caused ozone depletion has also been observed during several solar proton events in
the past 40 years. Model predictions indicate that the longer-lived SPE-caused polar stratospheric
ozone decrease was statistically significant, but less than 5 percent, in the Northern Hemisphere for the
extremely active 5-year time period average (2000-2004). Computations of total ozone do not indicate
any long-term SPE total ozone impact over the 1965-2004 period.
Galactic cosmic rays (GCRs) also create NO x and HO x constituents, but at lower altitudes
since these particles have much higher energies. The inclusion of GCR-created NO x constituents can
increase the odd nitrogen or NO y (N, NO, NO 2 , NO 3 , N 2 O 5 , HNO 3 , HO 2 NO 2 , ClONO 2 , BrONO 2 )
family in the lower stratosphere by up to about 20 percent, with small associated ozone decreases of
<2 percent. However, the variation in the GCR-driven change in NO y from solar maximum to solar
minimum is less than about 5 percent, which results in annually averaged total ozone variations of
<0.06 percent.
This talk will provide an overview of several of the EPP-related important processes and their
impacts on the atmosphere.
Cosmic Rays, Aerosols and Clouds
Jeffrey Pierce, Dalhousie University, Halifax, Nova Scotia
Cloud cover has been reported to correlate with the flux of galactic cosmic rays (GCRs) to the
troposphere, although these correlations are still controversial. Because the tropospheric GCR flux is
affected by solar activity, this GCR/cloud connection could be an important pathway for the Sun to
influence climate. However, we are just beginning to understand the physical pathways connecting GCRs
and clouds. The proposed pathways include (1) the ion-aerosol clear-sky hypothesis whereby GCRs
ionize gases and thus may enhance aerosol nucleation rates and cloud condensation nuclei concentrations,
and (2) the ion-aerosol near-cloud hypothesis whereby GCRs affect the charge distribution near clouds
and thus may affect the freezing of supercooled drops, which will affect precipitation. In this talk, I will
review the reported observations of GCR/aerosol/cloud correlations, discuss the proposed physical
pathways of GCRs affecting clouds, and present research evaluating the strength of the ion-aerosol clear-
sky hypothesis. I will conclude with thoughts on the next steps in GCR/aerosol/cloud research.
The Frequency of Solar Grand Minima Estimated from Studies of Solar-Type Stars
Dan Lubin, Scripps Institution of Oceanography, University of California, San Diego
The Maunder Minimum is a key event in climate change research (1) from the vantage point as a
natural control experiment in which greenhouse gas (GHG) abundances were at a pre-industrial constant
while solar forcing changed by a magnitude comparable to recent GHG increases, and (2) given recent
interest and speculation that a similar grand minimum might occur later this century. To date, periodicity
in solar grand minima has been difficult to detect in geophysical proxy data, and an alternative approach
involves estimating the frequency of the Sun's lifetime spent in a grand minimum state by searching for
evidence of grand minima in solar-type stars. Most often this is done by measuring calcium (Ca),
hydrogen (H), and potassium (K) flux as an indicator of chromospheric activity, or by photometric
observations of solar cycles on decadal timescales. Early estimates of grand minimum frequency in solar-
type stars ranged from 10 to 30 percent. However, these early studies inadvertently included many stars
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