FIGURE C.1 The 33-year total solar irradiance (TSI) record is the result of measurements made by several instruments. Measurement overlap helps correct for the majority of the differences between instruments, but improved instrument calibrations are needed to provide the required accuracies and stabilities in this solar climate data record for reliable climate studies. SOURCE: Courtesy of G. Kopp, University of Colorado.

improving position to understand the complex (and often subtle) ways that solar influences at high altitudes affect the lower atmosphere. This talk will discuss long-standing questions and recent progress in understanding this crucial aspect of the Sun-Earth connection.

Heliospheric Phenomena Responsible for Cosmic Ray Modulation at the Earth
Joe Giacalone, Department of Planetary Sciences, University of Arizona, Tucson

Galactic cosmic rays (GCRs) are essentially uniform in the space immediately outside Earth’s heliosphere and penetrate the solar system with very nearly equal probability from all directions. The GCR spectrum there is a smooth power law in energy over several decades. As they enter the solar system, GCRs suffer both spectral and intensity variations resulting from their interaction with the solar wind, interplanetary magnetic field, and heliosphere. The GCR intensity is known to anti-correlate with the number of sunspots on the Sun—having a higher intensity when there are few sunspots. This anti-correlation is the basis for using cosmogenic nuclei deposited in tree rings and ice cores as a proxy measure of solar activity dating back thousands of years.

In addition to the well-known 11-year cosmic-ray cycle, there is also a 22-year variation related to the polarity of the solar magnetic field. These variations can be interstood using the physics of charged-particle motion in turbulent electric and magnetic fields associated with the solar wind plasma. This talk will review the understanding of the physics of cosmic-ray transport, focusing primarily on the causes of the modulation of GCRs in the solar system. It will also discuss observations of cosmic rays from the recent long and deep sunspot minimum.

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