Q. What kind of data is used for predicting space weather?
Corona above an active solar region observed by HINODE (courtesy: NAOJ/JAXA)
Coronal mass ejection (CME) observed by SOHO. The white circle indicates the location of the Sun. (courtesy: SOHO/LASCO (ESA/NASA))
HINODE’s X-ray image of the Sun. The dark areas are coronal holes. Top image was taken on November 17, 2007; bottom image was taken on December 14, 2007. The coronal hole extending from the south returned 27 days later. (courtesy: NAOJ/JAXA)
Because we need information on the Sun, solar wind, geomagnetic fields and ionosphere, we use various observation data obtained by satellites and through ground observation. Our main data sources are:
• JAXA’s solar physics satellite HINODE
X-ray image data on coronal holes, where high-speed solar wind originates • SOHO, NASA/ESA’s Solar and Heliospheric Observatory Data on coronal mass ejections (CMEs) • SDO, NASA’s Solar Dynamics Observatory Data on sunspots, solar magnetic fields, and solar corona • STEREO, NASA’s Solar Terrestrial Relations Observatory Data on solar active regions and CMEs, observed from east and west of the Sun (as seen from Earth) • ACE, the Advanced Composition Explorer, NASA’s solar wind observatory Data on solar wind directly observed at about 1.5 million kilometers in the direction of the Sun from Earth (This real-time solar wind data is received from the spacecraft by an antenna at NICT headquarters.) • GOES, the Geostationary Operational Environmental Satellite, operated by the National Oceanic and Atmospheric Administration (NOAA) Data on X-rays and high-energy particles associated with solar flares, and high-energy electrons in geostationary orbit • NICT’s solar radio observation Data on CMEs • Geomagnetic observations by the Kakioka Magnetic Observatory of the Japan Meteorological Agency, and by NICT in Okinawa and Russia Data on geomagnetic variation associated with geomagnetic storms and auroral activity • Ionospheric observation by NICT using an observation instrument called an ionosonde Data on ionosphere, including information about sudden ionospheric disturbances (SIDs) associated with solar flares and ionospheric storms • Data from the GPS Earth Observation Network (GEONET), operated by the Geospatial Information Authority of Japan Data on total electron content (TEC) over Japan Q. How is space weather predicted? Space weather is predicted based on the time lag between the moment when an explosion on the Sun’s surface (i.e. a solar flare) happens and the time when high-energy particles released from the event reach the Earth. The distance between the Sun and the Earth is about 150 million kilometers. When a solar flare occurs on the Sun’s surface, X-rays take about eight minutes, and high-energy particles take from under an hour to a few hours to reach the Earth. Solar wind, which is observed by the solar wind observatory ACE, in orbit at the L1 Lagrangian point, reaches the Earth in about an hour. And a coronal mass ejection takes two to three days. We use these time lags to predict space weather.
For instance, if the ACE spacecraft has observed solar wind, we can make a pretty accurate prediction of a geomagnetic storm that will happen in about an hour. It’s similar to predicting seismic activity on the Earth: it is difficult to predict the timing and scale of an earthquake, but it is possible to predict the scale of the tsunami that follows, based on the location and strength of the quake. Solar flares and CMEs happen suddenly, so they are difficult to predict. But observing these events allows us to estimate the arrival time and scale of the high-energy particles that result.
As for coronal holes, we can predict space weather about a month ahead, based on the solar rotation period. Coronal holes are areas that appear dark in X-ray and extreme ultraviolet. They emanate high-speed solar wind, which can cause geomagnetic storms when blowing in the direction of the Earth. The Sun’s rotation period is about 27 days, so a coronal hole faces the Earth about once every 27 days. Using past data, and based on the size and location of a coronal hole, we can predict its possible impact on the Earth 27 days later.
In addition, as the behavior of the Sun has, on average, an 11-year cycle, we can presume active and quiet times of solar activity on a long-term basis. The last peak in the Sun’s cycle of activity was in 2000, so another peak should be observed again this year, in 2011. However, there is a slight delay in reference to past statistical data, and the next solar maximum is actually expected in mid-2013.
Q. Is space weather forecast in other countries, too?
Forecast centers of the International Space Environment Service (ISES) around the world. As of August 2011, 13 nations are participating in the ISES.
There is an international organization called the International Space Environment Service (ISES), which currently has 13 participating countries: the United States, Canada, Brazil, Australia, Japan, China, India, Russia, Poland, the Czech Republic, Belgium, Sweden, and South Africa. These countries share their data and forecast information.
Although many countries predict space weather, Japan has a long history of forecasting and has won international recognition. In the last few years, more countries, such as Korea, Brazil and Indonesia, have launched space weather programs, and we have assisted them with the start-up. Q. When and where did space weather forecast start? It began with predicting change in the space environment, which had an impact on high-frequency radio communications, and the first information was released in 1928, from the Eiffel Tower in Paris. Back then, it wasn’t called space weather forecast. In 1948, the predecessor of NICT, the Radio Research Laboratory, started researching and providing information about changes in the space environment for use in high-frequency radio communications. And in 1988, with the experience and knowledge accumulated since then, a research project for supporting space utilization, Space Weather Forecast, was launched. Similar research projects were launched in the United States and Europe later.
Some overseas researchers claim they were the first ones to use the term space weather, but we believe that the term "space weather forecast" originates in Japan.
