Study of coupling processes in the solar-terrestrial system

Outline
"Coupling processes in the solar-terrestrial system" aims to study the solar energy inputs into the Earth and the response of Geospace (magnetosphere, ionosphere, and atmosphere) to these energy inputs. Solar energy can mainly be divided into two parts: solar radiation and solar wind. The former involves infrared, visible, ultraviolet and X-ray, while the latter is the high-speed flow of plasma particles. Solar radiation is maximized at the equator. Atmospheric disturbances are actively generated near the Earth's surface and further excite various types of atmospheric waves, which propagate upward carrying energy and momentum. On the other hand, the energy associated with solar winds converges into the polar regions where disturbances are generated. Part of the energy is transported toward lower latitudes and lower atmospheric regions.
We propose to establish large atmospheric radars with active phased array antennas at the equator and the arctic region. In the equatorial region, we focus on the Indonesian region where atmospheric disturbances are most intense. We strive to establish a comprehensive observatory in Indonesia with the Equatorial MU (EMU) radar as the main facility. Additionally, we are part of an international collaboration to construct a state-of-the-art radar, called EISCAT_3D, in northern Scandinavia. We also develop a global observation network of portable equipment from the equator to both polar regions. With these radars and global network, we will study the flow of the energy and materials in the whole atmosphere. This project has been selected as an important project in both the Master Plan 2014 and 2017 by the Science Council of Japan. It has also been selected as one of top 11 projects in the Road Map 2014 by Japanese Ministry of Education, Culture, Sports, Science and Technology.

Outline

Equatorial Fountain
Cumulonimbus convection is active in the equatorial atmosphere. It generates various types of atmospheric waves that propagate upward to transport energy and momentum into the upper atmosphere, including the ionosphere. In addition, different kinds of materials (atmospheric minor constituents) originating at low- and mid-latitude regions that converge into the equatorial region are blown upward through the tropopause; they eventually reach the middle atmosphere and spread around the globe. In the upper atmosphere, there are plasma disturbances, and the equatorial ionization anomaly is generated around the equator. We will capture the energy and material flow occurring in all height ranges of the equatorial atmosphere as the "Equatorial Fountain" using the Equatorial MU (EMU) radar. In 2001 we established the Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia and continue our observations as part of an international collaboration. In this project, we propose developing the EMU radar, which is 10-times more sensitive than the EAR.
Equatorial Fountain

Research on energy input into the polar upper atmosphere and its response
The new IS radar "EISCAT_3D" provides great opportunities to make major breakthroughs in the science of solar-terrestrial physics. High-energy particles precipitate from the magnetosphere into the polar upper atmosphere along Earth's magnetic field lines and create interesting phenomena such as the aurora borealis. Part of the energy from the solar wind changes its form and is transported to the lower atmosphere and lower latitude regions. On the other hand, the polar region is also the area where part of the Earth's atmosphere outflows to Space. The phenomena occurring in the polar upper atmosphere are characterized by their rapid variability in time and space. The EISCAT_3D radar will have the unique capability to investigate three-dimensional structures of the upper atmosphere and ionosphere with a high temporal and spatial resolution. As part of an international collaboration with the EISCAT scientific association of which Japan has been a member since 1996, we will help construct the EISCAT_3D radar system in northern Scandinavia.
Equatorial Fountain

Global observation network
We developed the MU radar in Japan, which is the first application of an active phased array antenna to atmospheric radars. This technology has been extended to similar radar systems in overseas bases. Additionally, foreign researchers have adopted our innovation to develop other radars. Based on this heritage, we will establish even more advanced state-of-the-art radars in the equatorial and polar regions. On the other hand, we have deployed observation network of small instruments to the Asian and African regions where observations were not well established. We will move to expand the observation network from the equator to the poles, establish an international collaboration of large radars, share data through IUGONET, and elucidate the global flow of energy and materials.
Global observation network
IUGONET

National and international research trends
The study of the coupling processes in the solar-terrestrial system has been internationally discussed by SCOSTEP (Scientific Committee on Solar-Terrestrial Physics) under ICSU (International Council for Science). Japan's contribution was determined through discussions at the Science Council of Japan (SCJ). Since the International Geophysical Year (IGY in 1957-1958), many international research programs lasting about five to ten years have been undertaken. For example, VarSITI (Variability of the Sun and Its Terrestrial Impact) (2014-2018) replaced the CAWSES (Climate and Weather of the Sun-Earth System) (2004-2013).
Japan has contributed greatly through observations, especially via the deployment of large atmospheric radars. We developed the MU radar in Japan in 1984, the Equatorial Atmosphere Radar (EAR) right over the equator in 2001, joined EISCAT scientific association to enhance observations of the polar-region in 1996, and recently developed the PANSY radar at the Antarctic Syowa station. In parallel to these efforts, our observation network of magnetometers and airglow imagers were expanded to large areas all over the world. To enhance the management and use of the large amount of data from observations with these facilities, we are now running a project called IUGONET (Inter-university Upper atmosphere Global Observation NETwork).
National and international research trends

National/International cooperation
This plan is widely supported by national and international scientific communities. The development of the Equatorial MU radar has received full support from the Indonesian Government, similar to the EISCAT_3D project, which progressed due to international discussions with the associated countries in Europe and China. We have been pioneering atmospheric radars with innovative technology. Leveraging our knowledge of solar-terrestrial studies, we continue to lead international research. We have already established a consortium for mutual use of large-volume data from our observations. These data will be used in the World Data System, and will be an example of "big data".

Effect from the plan and capacity building
Understanding the solar-terrestrial system may advance studies on the atmospheric environment of extra-solar planets. The development of new radar has a direct impact on radio science, informatics, and electronics. The results from our studies should improve the forecast accuracy of severe weather and/or space weather.
Through field practice and international school, the project will be useful for capacity building of young scientists from around the world, and can also contribute to peaceful diplomacy through science and technology exchanges.

Related overseas institutions
Indonesia: RISTEKDIKTI (Ministry of Research, Technology and Higher Education), LAPAN (National Institute of Aeronautics and Space), BMKG (Indonesian Agency for Meteorology, Climatology and Geophysics), BPPT (Agency for the Assessment and Application of Technology), ITB (Bandung Institute of Technology), etc.
EISCAT science association: Established in 1975 by Germany, UK, France, Norway, Sweden, and Finland. Japan and China joined in 1996 and 2007, respectively.

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