Basic Study of Space Weather Predictions: A New Project in Japan

In order to have successful space weather predictions, scientists must have a good physical model of solar-terrestrial phenomena. This model should deal with the key processes, spanning from solar flares and coronal mass ejections on the Sun to geomagnetic storms and their effects in the upper atmosphere of Earth. To reach this goal, a number of fundamental questions must first be solved. For example: What is the triggering condition of solar flares? How do coronal mass ejections form? What is the mechanism of particle acceleration? What are the mechanisms of geomagnetic storms and substorms? Solving these basic questions is equivalent to understanding multiscale coupling of various physical processes occurring on different scales. This is partly what space weather research aims to accomplish, because finding empirical formulas without understanding physical processes will not lead to successful predictions of all space weather events. To acknowledge these basic science needs, a new space weather project entitled “Basic Study of Space Weather Predictions” is under way in Japan, funded by the Grant-in-Aid for Creative Scientific Research from the Ministry of Education, Science, Sports, Technology, and Culture of Japan. The purpose of this project is to develop a physical model of solar-terrestrial phenomena and space storms as a basis of space weather prediction by resolving fundamental physics of key phenomena from solar flares and coronal mass ejections to magnetospheric storms. The Basic Study of Space Weather Predictions project is run under the international cooperation of the Climate and Weather of the Sun-Earth System (CAWSES) program, which is currently managed by the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP). The project, which began in 2005, will last for 5 years, with a total budget of 446.4 million yen (roughly US$4 million). Eleven principal investigators representing research groups in Japan are directly funded through the project, though the number of researchers practically involved in this project is as many as 50. The entire team is divided into four subgroups that have distinct areas of focus: energy release mechanisms on the Sun, solar wind modeling from interplanetary scintillation observations, real-time observations and space weather maps, and virtual observatories. Combining all these efforts, we will develop a multiscale coupling model of space weather phenomena, which can be utilized not only to forecast major geomagnetic storms but also to reproduce the observations in the Sun-Earth system. Once developed, this model will be used by Japan's National Institute of Information and Communication Technologies (NICT) and other institutes and agencies to forecast adverse space weather. Our project is different from other space weather projects of the past. In particular, it is quite timely to carry out this project at the present time because the Hinode spacecraft (renamed from Solar-B) and the STEREO missions were successfully launched in 2006, allowing scientists the opportunity to use new, detailed data sets in their modeling efforts. Further, the umbrella of the CAWSES program helps to make active international collaborations possible. Moreover, a special role of our project is to enhance close communications between solar physicists and geophysicists both domestically and internationally. This link is essential for the success of space weather research. Several subgroups of the Basic Study of Space Weather Predictions project have unique attributes. The rest of this article describes these subgroups in more detail. The Sun is the ultimate energy source for space weather phenomena, and hence its observations are fundamentally important, providing key input parameters to the Sun-Earth system. Members of this subgroup will study the energy release and triggering mechanisms of flares and coronal mass ejections using both ground-based observations with the new Solar Magnetic Activity Research Telescope (SMART) at Hida Observatory of Kyoto University (http://www.hida.kyoto-u.ac.jp/~smart/; see Figure 1) and space observations with the Hinode satellite (http://solar.nro.nao.ac.jp/solar-b/index_e.shtml). In particular, Hinode data will allow scientists to measure for the first time vector magnetic fields from space, optical and X-ray images, and extreme-ultraviolet lines at the highest possible spatial resolution. In relation to the above observations by SMART, international collaborations on the Continuous H Alpha Imaging Network (CHAIN), an international project proposed by Japanese scientists that helps to connect telescopic observations of the Sun throughout the world, are also being implemented. CHAIN is a natural extension of the Global High-Resolution H Alpha Network, a collaboration by seven solar observatories around the world that enables 24-hour continuous full-Sun observations of the hydrogen spectral line, useful to understanding the Sun's dynamic corona. Where the Global High-Resolution H Alpha Network focuses its observations on a narrow spectral range, CHAIN widens this spectral window by a factor of 3 to include H alpha red and blue wings in addition to the H alpha center. Using these H alpha observations, scientists will be able to observe the waves responsible for fast moving magnetohydrodynamic shocks, a critical space weather driver, along with the continuous evolution of solar filaments from their formation to eruption. Knowledge of these filaments is essential for prediction of solar flares and coronal mass ejections. Simultaneously, Hinode observations of the vector magnetic field for active regions, supplemented by the full-Sun vector magnetogram generated by SMART, would unveil the detailed structure of the magnetic field in active regions, hopefully providing scientists with answers to questions such as how free magnetic energy is stored in active regions and what triggers flares and coronal mass ejections. Solar wind data are taken with the ultrahigh-frequency (327 MHz) radio telescope at the Solar-Terrestrial Environment Laboratory of Nagoya University through the interplanetary scintillation method. The telescope system is being upgraded so that scientists can double the number of observable events they are able to view. Additionally, data on interplanetary scintillation (IPS), which is caused by the scattering of radio waves coming from distant stars by electron density fluctuations in the solar wind, will be synthesized three-dimensionally using a tomography technique (see http://casswww.ucsd.edu/solar/tomography/fast_stel_1965.html for the analysis technique and various examples). By observing IPS patterns, scientists can estimate the spatial distribution of various quantities of the solar wind, such as density fluctuations and velocity of the solar wind. With these data sets, scientists will develop a three-dimensional (3-D) model of the structure and dynamics of the solar wind and interplanetary coronal mass ejections (ICMEs), partly using 3-D magnetohydrodynamic simulations. Modeling efforts using such data would be extremely useful to estimating solar wind speed near Earth and the propagation of ICMEs. Using ground-based magnetometer data as well as solar wind data, all in near real-time, space weather maps revealing ionospheric electric potential and current distributions are now available at 5- to 10-min intervals (see Figure 2 and http://gedas22.stelab.nagoya-u.ac.jp/rtkrm/link/). Project scientists will upgrade this magnetogram-inversion algorithm so that it can accommodate other types of real-time observations, including global auroral images and radar data. In this way, calculations of the ionospheric conductances, which are essential in the inversion technique, can be given more accurately. Using output of the ionospheric potentials from these weather maps, magnetosphere-ionosphere-thermosphere coupling as well as solar wind–magnetosphere coupling can be studied in more detail. For example, computer simulations and predictions of the thermospheric wind system can be significantly improved if scientists use the real-time electric potentials in the polar ionosphere, a quantity provided by this group of scientists. It will also become possible to trace particles in the magnetosphere under the electric field distribution mapped from the ionospheric level. Basic physical processes such as the formation of the ring current encircling Earth during geomagnetic storms and the occurrence of turbulence and particle acceleration in the inner magnetosphere will also be studied as a basis of space weather research. Critical to generating these models will be housing all these data and allowing users to access the wealth of information that the Basic Study of Space Weather Predictions project is producing. To this end, “virtual observatories” will be developed from numerical modeling using actual data of the Sun-Earth system as the boundary conditions, enabling scientists to estimate any data at any locations in space between the Sun and the terrestrial atmosphere. For this purpose, scientists will first develop a reliable software system connecting various observations including both solar and geophysical data. The new data taken with the new observing instruments shown above will be synthesized as well. They will also develop a numerical modeling scheme, which will make it possible to run global simulations from the solar atmosphere to the Earth's atmosphere, using actual data as initial conditions. Observations and modeling play complementary roles here: Modeling results can be tested by real-time observations, whereas the lack of observations is compensated for by modeling. These virtual observatories will be a powerful tool for numerical space weather predictions. Japan's concentrated effort to develop space weather prediction capabilities represents a significant push toward advancing the field of space weather research as a whole through better characterizing the Sun-Earth system (see Figure 3). Through using SMART and Hinode data, now open to the world, scientists are in the midst of developing numerical models of the solar wind and are now focusing their efforts on better characterizing solar flares and coronal mass ejections. Further, building virtual observatories and data archive systems will allow users around the world to access Hinode and SMART data, as well as other types of solar-terrestrial data useful for space weather studies. Such data archives will actually drive new discoveries by allowing scientists to readily conduct numerical modeling of space weather phenomena from the solar atmosphere to the Earth's atmosphere. Critical to this will be communication between different fields, especially between the solar physics and geophysics communities. By providing a pathway by which the whole Sun-Earth system is analyzed, Japan's Basic Study of Space Weather Predictions project will foster this discussion, helping to unite the branches of space weather science. Kazunari Shibata is a professor of physics and astronomy at the Graduate School of Science, Kyoto University, and the director of the Kwasan and Hida observatories of Kyoto University. He is also the lead investigator for the Basic Study of Space Weather Predictions project. E-mail: shibata@kwasan.kyoto-u.ac.jp. Yohsuke Kamide is a professor at the Research Institute for Sustainable Humanosphere of Kyoto University and the former director of Nagoya University's Solar Terrestrial Environment Laboratory. E-mail: kamide@rish.koto-u.ac.