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In recent years, the expression “solar storm” has become popular in China, but many Chinese do not realize that solar storms are very different from storms on Earth. As solar physicists and members of the Regional Warning Center China (RWCC) of International Space Environment Services (ISES), we frequently encounter the question “What is a solar storm? ” In order to properly respond to the customers of the RWCC, we investigated the historical evolution of the term “solar storm. ” On 1 September 1859, Richard Carrington observed a sizable flare in a large area of the Sun in which there was a group of spots [Carrington, 1859]. A severe geomagnetic storm followed, which resulted in worldwide electromagnetic disruptions of telegraph systems. However, the electromagnetic connections between solar eruptions and geomagnetic storms remained unknown until solar magnetism was revealed in the twentieth century. For a long time, any disfigured area on the Sun, whether stained by one spot or by many, was regarded as a solar storm [O'Halloran, 1904]; we now classify such areas as active regions. Since the discovery of strong magnetic fields in sunspots [Hale, 1908], it has been widely believed that the energy of solar eruptions is released through variations of solar magnetic fields. In geophysics and space science, the word “storm” has been employed to describe violent disturbances in Earth's magnetosphere. Magnetic storms were first observed and studied by Alexander von Humboldt at the beginning of the nineteenth century [Malin and Barraclough, 1991], and polar elementary storms (magnetic substorms) were first observed and studied at the beginning of the twentieth century [Birkeland, 1908, 1913]. Today, ground-based and spaceborne solar observations reveal that a solar storm can be regarded as an event in which disturbances caused by solar eruptions, such as major solar flares and coronal mass ejections, propagate through interplanetary space, creating shock waves in the solar wind. These shock waves interact with the geomagnetosphere and subsequently affect the ionosphere and the atmosphere. Thus, geomagnetic and ionospheric storms are caused by disturbances from the Sun. Electromagnetic radiation, energetic particles, and magnetic clouds involved in a solar storm all pose threats to human technological systems. Historically, solar storms have often interfered with satellites, communication systems, and power grids, resulting in interruptions and damage. Modern society relies on high‐tech systems that are strongly supported by electromagnetic technologies. As pointed out by National Research Council [2008], highly developed countries might be the most vulnerable to the effects of solar storms. In this sense, therefore, the term “solar storm” is equivalent to “electromagnetic storm”: the concept of a solar electromagnetic storm logically explains the physical effects that major solar eruptions have on the space environment and thus on Earth technology. With this understanding, it is easier for customers of the RWCC to comprehend that humans must prepare for not only geological and meteorological disasters but also electromagnetic disasters. On the other hand, from the point of view of basic research in solar and stellar astrophysics, the term “solar electromagnetic storm” clearly indicates that the ultimate cause of solar and stellar activity is the ubiquitous electromagnetic interaction in the universe. For example, recent statistical analyses of observations from solar‐type stars show that superstar electromagnetic storms are occurring in all of these star systems [Maehara et al., 2012], which might have not only complicated structures but also electromagnetic interactions. Such discoveries will be expanded upon in future solar and stellar research endeavors. Acknowledgments The authors wish to acknowledge the Editor for valuable suggestions. This work is supported by the National Basic Research Program of China (973 Program) through grant 2011CB811406 and the National Natural Science Foundation of China through grant 10921303. References Birkeland, K. (1908), The Norwegian Aurora Polaris Expedition 1902‐1903, sect. 1, H. Aschehoug, New York. [Available at http://www.archive.org/details/norwegianaurorap01chririch.] Birkeland, K. (1913), The Norwegian Aurora Polaris Expedition 1902‐1903, sect. 2, H. Aschehoug, New York. [Available at http://www.archive.org/details/norwegianaurorap01chririch.] Carrington, R. C. (1859), Description of a singular appearance seen in the Sun on September 1, 1859, Mon. Not. R. Astron. Soc., 20, 13-15. Hale, G. E. (1908), On the probable existence of a magnetic field in Sun‐spots, Astrophys. J., 28, 315‐343. Maehara, H., T. Shibayama, S. Notsu, Y. Notsu, T, Nagao, S. Kusaba, S. Honda, D. Nogami, and K. Shibata (2012), Superflares on solar‐type stars, Nature, 485, 478-491, doi:10.1038/nature11063. Malin, S. R. C., and D. R. Barraclough (1991), Humboldt and the Earth's magnetic field, Q. J. R. Astron. Soc., 32, 279-293. National Research Council (2008), Severe Space Weather Events‐Understanding Societal and Economic Impacts: A Workshop Report, Washington, D. C. [Available at .] O'Halloran, R. (1904), Some details of the recent solar cycle, Popular Astron., 12, 27-32. The Regional Warning Center of China is headquartered in National Astronomical Observatories, Chinese Academy of Sciences (NAOC). Huaning Wang is a delegate and deputy director of RWCC in ISES and a member of the Key Laboratory of Solar Activity, Chinese Academy of Sciences. E-mail: hnwang@bao.ac.cn. Guoxiang Ai is an academician of Chinese Academy of Sciences and former director of NAOC. E-mail: aigx@nao.cas.cn. JingxiuWang is a professor of NAOC, editor-in-chief of Research in Astronomy and Astrophysics, and an editorial board member of Solar Physics. E-mail: wangjx@nao.cas.cn. Citation: Wang, H., G. Ai, and J. Wang (2012), What Is a Solar Electromagnetic Storm?, Space Weather, 10, S09003, doi:10.1029/2012SW000847. Copyright 2012 by the American Geophysical Union. |
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