Solar Modulation of the galactic cosmic rays and the production of cosmogenic isotope archives of long-term solar activity, used to interpret past climate changes.

Team Chair: Petrus Martens
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Team-Maintained Web Site: http://solar.physics.montana.edu/solaractivity/
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Target Description: This topic addresses the physical processes that relate variations in solar radiative output to the variable flux of cosmic rays that produce cosmogenic isotopes. Cosmogenic isotopes (14C and 10Be) archived in tree-rings and ice-cores, respectively, provide unique information about levels of solar activity over many thousands of years prior to the early seventeenth century, when sunspot observations commenced. Correlations of many paleoclimate variables (e.g., 18O indicators of temperature or precipitation) with the cosmogenic isotopes suggest that climate has been responding to solar forcing throughout the Holocene. Even though cosmogenic isotopes vary in response to the flux of galactic cosmic rays at Earth, and thus to modulation of the heliosphere by open magnetic flux, the correlations are typically attributed to variations in solar radiative output, which arise from changes in the closed magnetic flux that produces features in the solar atmosphere such as sunspots and faculae.

Needed for reliable interpretation of paleo Sun-climate relationships is a physics-based understanding of the relationship between radiative output and cosmogenic isotopes that takes into account the quite different processes within the entire Sun-Earth system that produce their variations.

Goals and measures of success: The goal is to identify and characterize the respective solar-driven processes that simultaneously, but by distinctly different processes, modulate both solar radiative output and heliospheric structure, composition and hence the flux of galactic cosmic rays. A measure of success is a quantitative relationship between time series of solar radiative output and cosmogenic isotopes, on multiple time scales. Other measures of success include improved specification of cosmic ray transport/ attenuation in the heliosphere, and/or deposition/transport in the Earth’s atmosphere as functions of solar activity.

Types of solicited investigations: Relevant investigations include empirical and model investigations of the organization of solar magnetic fields into closed and open flux, as a result of transport by solar differential rotation, diffusion and meridional flow. Quantitative determinations of the solar-driven heliospheric modulation of galactic cosmic rays by transport, attenuation and interactive processes are also relevant, as are investigations of other physical processes within the Sun-Earth system needed to quantitatively relate electromagnetic radiation and cosmogenic isotopes. Studies of the deposition and transport of the cosmic ray fluxes in the Earth’s atmosphere are also solicited.