Research

  The Sun is a dynamic star whose magnetic activity shows long-term variations on centennial and longer time scales in the amplitude of the 11-year cycles. When the Sun is active, solar flares occur more frequently, releasing energetic radiation and particles into space. These disturbances drive space weather around Earth, affecting satellites in orbit, disrupting communication and navigation systems, and even posing challenges to human space exploration.

  Our unit analyzes carbon-14 in tree rings and beryllium-10 in sediments and ice cores to investigate the cyclic behavior of solar activity and past extreme solar flare events to understand their characteristics. We are particularly interested in the modulation of the 11-year cycles, which reflects the flow speed in the solar convection layer, as this offers a key to understanding the mechanisms of solar activity variations and improving our ability to predict future solar activity.

  The radiation environment of the Earth is determined by the condition of the heliosphere, an expansion of the solar magnetic field carried outward by the solar wind. The heliosphere acts as a protective shield against galactic cosmic rays, and its size and structure vary with solar activity. The variations of carbon-14 and beryllium-10, produced by galactic cosmic rays, reflect not only solar activity but also the large-scale structure of the heliosphere. Through the analyses of these cosmogenic isotopes, our unit aims to understand the variability of the heliosphere and its influence on the radiation environment of the Earth.

  While various direct and proxy-based observations of climate indicate synchronous variations with solar activity, the underlying mechanisms are not yet fully understood. The total amount of solar irradiance shows only limited variability, and therefore, the observed climate responses, such as the glacier advances during the Little Ice Age, cannot be explained by irradiance alone.

  Our unit investigates how the Earth’s climate system responds to solar activity variations at various time scales, with particular interest in the roles of clouds and atmospheric and oceanic processes.