Project for Solar-Terrestrial Climate Research
Interdisciplinary collaborative research project
"Project for Solar-Terrestrial Climate Research"
Solar activity, which corresponds to the sunspot number, shows an 11/22-year cycle; however, it undergoes long-term variability on cycles ranging from decades to several thousand years. As long-term solar activity has coincided with terrestrial climate varying over several thousand years, many researchers have reported that long-term solar activity as well as volcanic activity may be one of the reasons for natural climate variability. In particular, the years between the 1650s and the 1700s are well-known as the Maunder Minimum, during which the sunspot number was significantly small and the terrestrial climate was reported to have fallen into the so-called Little Ice Age.
However, the physical processes by which solar activity affects terrestrial climate variations is not very clear; therefore, understanding the physical process is not only one of the main scientific issues in solar-terrestrial environmental research, but it also contributes to our understanding of the current climate warming trend, as well as our ability to predict climate variations in the near future. Because current solar activity (cycle 24) is considered to be the lowest in the last few decades, most solar-terrestrial environmental researchers have considered that solar activity may be shifting back into a quiet phase in the near future. Therefore, revealing how solar activity affects the terrestrial environment in the 21st century is an important issue both scientifically and socially.
This research project aims to reveal how solar activity affects the terrestrial climate and environment with a collaboration between researchers from fields such as solar physics, meteorology, oceanography, paleoclimatology, space physics, and cosmic ray physics. This collaborative research focuses on the following issues, which will be studied by both domestic Japanese and international researchers:
- Paleo-environmental and solar activity data from the past will be reconstructed at high resolution using tree rings, ice cores, and permafrost (see Appendix 1).
- Nitrogen oxides and hydroxide, both of which are produced by intrusions of high-energy charged particles (i.e., galactic cosmic rays) accelerated by solar flares into the atmosphere, will be measured over the Antarctic.
- The physical mechanisms of variations in sunspot number will be revealed using numerical simulations compared with observation data. Based on this analysis, total solar irradiance in the recent past, as well as the near future, will be projected along with terrestrial climate change.
- The effects of solar radiation, high-energy charged particles, and cosmic rays on the terrestrial climate and environment will be analyzed using several Earth system models. Future projections of such effects will also be actively performed.
Appendix 1：Solar wind and the interplanetary magnetic field (IMF) fill the heliosphere, and the intensity of IMF changes in an 11-year (or 22-year) cycle, which corresponds to the solar cycle. Because solar activity originates from sunspots, the intensity of the IMF corresponds to the sunspot number. However, high-energy charged particles, i.e., galactic cosmic rays, arrive from outside the heliosphere and can be scattered by the IMF as well as the magnetosphere, which originates from the geomagnetic field. Thus, their intrusion into the magnetosphere highly depends on the solar activity as well as the geomagnetic intensity.
Note that galactic cosmic rays produce radioactive isotopes in the terrestrial atmosphere, which are called as cosmogenic isotopes, with the collapse of atmospheric atomic reactions. The production rate of the cosmogenic isotopes corresponds to the intensity of galactic cosmic ray intrusions into the atmosphere. Thus, both solar activity and geomagnetic intensity suppress the production rate of the cosmogenic isotopes. The most representative cosmogenic isotopes in our research fields are radiocarbon (14C) and beryllium-10 (10Be). The half-life of 14C is 5730 years and that of 10Be is 1.51 million years. This research project uses our TANDETRON Accelerator Mass Spectrometer to measure 14C and 10Be and to extract long-term paleo-environmental data with a focus on solar activity and geomagnetic intensity.