The solar EPP-created NOx family has a longer lifetime than the HOx family and can also lead to catalytic ozone destruction. EPP-caused enhancements of the NOx family can affect ozone promptly, if produced in the stratosphere, or subsequently, if produced in the lower thermosphere or mesosphere and transported to the stratosphere. NOx 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 NOx enhancements in the upper mesosphere and lower thermosphere to lower altitudes.

The NOx-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 also create NOx and HOx constituents, but at lower altitudes since these particles have much higher energies. The inclusion of galactic cosmic ray-created NOx constituents can increase the odd nitrogen or NOy (N, NO, NO2, NO3, N2O5, HNO3, HO2NO2, ClONO2, BrONO2) 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 NOy 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 to the troposphere, although these correlations are still controversial. Because the tropospheric galactic cosmic ray 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),



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