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The Forefront of Space Science

Science of Space Weather
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When the CRL was reorganized in 2001, my colleagues and I started real-time simulation of the earth’s magnetosphere inputting the solar-wind parameters. In short, we started space-weather forecasting for the magnetosphere. In the course of our research, we discovered that the emergence of aurora corresponded to changes in the magnetosphere’s topology. Specifically, energy released from the magnetic fields facilitates the increase in plasma pressure and motion to directly cause aurora and magnetic storms. Today, as our knowledge of terrestrial storms deepens, research moved to the next stage where we are able to model solar winds from observation data of the solar surface. Meanwhile, the research group has extended throughout Japan. Space-environment simulations are now being conducted at Kyushu University, Meteorological College, and the National Institute for Fusion Science.

Moreover, we are participating in the Grant-in-Aid for Creative Scientific Research “Basic Research of Space Weather ForecastingE(representative: Prof. Kazunari Shibata, Kyoto University) by the Ministry of Education, Culture, Sports, Science and Technology (MEXT). In the project, we are conducting research into space-environment modeling.

The most important but most difficult issue is to forecast the emergence of solar flares. The solar-observation satellites YOHKOH and HINODE are gradually elucidating the mechanism of solar-flare occurrence. X-ray telescopes onboard the satellites observed that magnetic lines over sunspots twisted greatly to store energy and, occasionally, the release of that stored energy coincided with changes in the lines. On reflection, topological changes in the magnetic lines are very similar to the emergence of aurora in the terrestrial magnetosphere. This comes as no surprise since both solar corona and the terrestrial magnetosphere are composed of plasma and magnetic fields. We are advancing our research on the assumption that space-plasma physics would elucidate solar and terrestrial storms.

Figure 4
Figure 4. Simulation of the Earth’s magnetosphere

To prevent damage by space environment - In place of a conclusion

By directly observing space environment with satellites, etc., the JAXA space-environment group is conducting monitoring the Van Allen belt electrons that increase due to terrestrial storms or the invasive mechanisms of solar cosmic rays from solar flares. The impact of high energy particles appears in devices onboard satellites. Our space environment group tackled the task of quantitatively estimating the radiation environment around satellites as part of the development of radiation-hardened space devices. We also analyzed space-environment conditions at the time of satellite malfunctions to contribute to the investigation into the causes. Changes in the space environment caused situations where satellites were strongly charged or their attitudes were greatly disturbed by atmospheric inflation.

Through these experiences, we have decided it is desirable to build satellites resilient to changes in the space environment. Currently, we are participating in JAXA’s satellite design standard-revision project and presiding over the space-environment working group. The revision of satellite design standards is being implemented for all technology areas as an imminent and critical task. Many working groups were established for the task. We are also part of the electrical charge and device working groups and are promoting cooperation with specialists in space engineering.

The mission of space-environment research is to protect the safety of satellites and astronauts from the harsh space environment. In this article, I have concentrated on the degree to which we can forecast solar and terrestrial storms. At the end of our science research, we face the huge technological challenge of developing strong satellites. JAXA’s space-environment research is being advanced from the aspect of science and technology as two wings on a single plane.

Takahiro Obara

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