Corresponding author: T. Nagatsuma, Space Weather and Environment Informatics Laboratory, Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology, 4-2-1 Nukui-kita, Nukui-kita-machi, Koganei, Tokyo 184-8795, Japan. (email@example.com)
Introducing current activities of Japanese space weather forecast
Future direction of Japanese operational space weather research
Historical background of Japanese space weather forecast
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The origin of Japanese space weather forecast comes from the forecast of radio wave broadcasts which provide current and future conditions of radio wave propagation for telecommunications. The Japanese radio wave forecast service began in the 1940s. To improve the reliability of long-distance telecommunications by radio waves, the subject “solar activity effect to the ionosphere” was extensively studied in the 1950s. During these research activities, the relationships between radio propagation and solar microwave bursts and sudden ionospheric disturbance were examined. Further, polar cap absorption events were studied and their relationships with type IV solar radio bursts were discovered. Present-day space weather research and operations in Japan originated from this positive interaction between basic research and practical needs in this earlier era [Nishida, 2010].
With the passage of time, the importance of radio wave communications has decreased due to the establishment of the wired-communication network. In contrast, activities of space research and development are continuing to grow in Japan based on our nation's rocket and satellite technologies. Because of this historical background of radio wave forecasting beginning in the 1940s, it can be stated that the world's first “space weather” forecast program was started in 1988 by the Communications Research Laboratory (currently, the National Institute of Information and Communications Technology (NICT)) [Marubashi, 1989].
Forecasting Operation and Information Services
Japanese operational space weather forecast is currently provided from the Space Weather and Environment Informatics Laboratory in NICT. Since NICT's space weather forecast center belongs to the International Space Environment Service as the Regional Warning Center Japan, our operational activities are supported by international cooperation. Solar flare, geomagnetic activity, high-energy particles (proton event and relativistic electrons in the radiation belts), and conditions of radio wave propagation are predicted based on the analysis of current conditions and trends of space weather activities. A forecaster's meeting is held from 14:30 JST (05:30 UT) each day for discussing the final decision of the current day's space weather forecast (Figure 1). The latest data and simulation/model outputs ranging from the Sun to Earth's upper atmosphere are consulted.
Information service is one of the key elements of space weather forecasting in the NICT, because forecasting activities should be widely provided to the public. Forecasting information and an online database of space weather monitoring were provided via computer network before the internet era. NICT also attempts to provide new types of forecasting information for citizens who are not familiar with space weather itself. NICT has made a short movie to explain the technical terms of space weather (Figure 1). This type of information, with many images, is very useful for nontechnical people to understand space weather forecasts.
Major users of NICT space weather forecasts in Japan include radio amateurs, geophysical prospecting companies, aurora tourists, satellite operators, airline companies, and power line companies. The needs of the users are important for improving and upgrading NICT forecasting information. However, it is usual that users do not make any active requests. Therefore, to understand the exact needs and practical usage of space weather forecasts, NICT organizes a “user's forum for space weather” every few years. The user's needs collected from the forum form the seeds of practical research and operational activities in the future. More than 50 participants attend each forum. Tutorial talks about space weather phenomena and how to interpret the data, charts, and products that NICT produces are provided. Invited talks from users explain how they use NICT space weather forecasts.
NICT's Space Weather Monitoring Networks
One of the fundamental components of weather forecasting is to understand the current conditions of an environment. In the case of space weather forecasting, a network of observations from the Sun to the Earth's upper atmosphere is essential. NICT has constructed comprehensive ground-based networks for space weather monitoring along the Japanese meridian from the pole to the equator. These networks are used for operation and research of space weather forecasting [Nagatsuma et al., 2012] (see Figure 2). Most of the data obtained from the networks are available in near real time for space weather monitoring. These data are also useful for advanced research of space weather phenomena and for validation of space weather simulations and models. Further, the data can be applied to future data assimilation of space weather modeling.
Current conditions of geomagnetic disturbances and ULF wave activities are monitored by ground-based magnetometer networks and HF radar at King Salmon. Some of the magnetometers are operated by the international project Russian Auroral and Polar Ionospheric Disturbance Magnetometers (RapidMAG) [Takahashi et al., 2004]. The HF radar at King Salmon is operated as a part of the Super Dual Auroral Radar Network (SuperDARN) [e.g., Chisham et al., 2007]. The South-East Asia Low-latitude IOnospheric Network (SEALION) is a unique network of observations for ionospheric disturbances in the equatorial region [Maruyama et al., 2007].
NICT has also developed a high-resolution ionospheric total electron content (TEC) observation system using a dense Global Navigation Satellite Systems (GNSS) receiver network in Japan [e.g., Tsugawa et al., 2007a], North America [Tsugawa et al., 2007b], and Europe [Otsuka et al., 2013]. The 2-D GNSS-TEC observations are very useful to monitor spatial structures and temporal evolutions of various ionospheric phenomena such as plasma bubbles, travelling ionospheric disturbances, and storm-enhanced density. To expand the TEC observation area, NICT has collected all available GNSS receiver data worldwide and conducted a project to share the data and/or information among countries, especially in the Asia-Oceania region.
Near–real-time solar wind data are acquired from the ACE and STEREO spacecraft using 11 m antennas in NICT [Zwickl et al., 1998; Biesecker et al., 2008].
Many types of near–real-time data and other products are available from other organizations using high-speed networks and advanced information technologies. While these are useful for space weather forecasting, maintaining NICT's own regional observation network is one of the important tasks of Japanese operational space weather forecast and advanced study.
Space Weather Simulation and Modeling
As noted above, fundamental information for space weather forecasting is based on the decision of the daily forecaster's meeting. That is, NICT relies on manual judgment for deciding today's space weather forecast. On the other hand, NICT is developing a space weather numerical simulation code for future objective and advanced space weather forecasts. Numerical simulation is also important for understanding the global processes of space weather, because the entire structure of the Sun-Earth system cannot be visualize solely from observations.
A magnetospheric global MHD simulation code has been developed for understanding physical processes of space weather as a compound system [Tanaka, 1994, 1995; Tanaka et al., 2010]. To achieve high-resolution and excellent shock-capturing capabilities, the numerical model employs the finite volume total variation diminishing scheme with an unstructured grid system [Tanaka, 1994]. Since 2004, NICT has operated the first real-time Earth magnetosphere simulator based on the Tanaka global MHD code [Den et al., 2006; Shimazu et al., 2008]. The input parameter of this simulator is real-time solar wind data obtained from ACE. Since this simulator can calculate conditions of Earth's magnetosphere within 1 h (which is less than the solar wind transit time between ACE and Earth), real-time magnetospheric conditions can be estimated based on this simulator. NICT has also developed a 3-D MHD simulation model of the solar surface–solar wind system. Based on comparisons with observations, it is confirmed that the MHD model successfully reproduces many features of both the fine solar coronal structure and the global solar wind structure [Nakamizo et al., 2009].
With respect to ionospheric and thermospheric disturbances, modeling effects from the lower atmosphere is necessary. Therefore, NICT is developing an Earth's whole atmosphere model from the troposphere to the ionosphere, called GAIA (The Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy) [Jin et al., 2011]. The GAIA model has been recently developed by coupling three models: a whole atmosphere general circulation model [Miyoshi and Fujiwara, 2003], an ionosphere model [Shinagawa, 2009], and an electrodynamics model [Jin et al., 2008]. The GAIA model solves the ionosphere-thermosphere interaction self-consistently, including the electrodynamics. The simulation reproduces and confirms the vertical coupling processes proposed so far with respect to the formation of the averaged longitudinal structure of equatorial ionospheric anomalies. Although these numerical simulations are still far from practical use, these approaches are very important for future advanced numerical space weather forecast (Figure 3).
To satisfy the requirements of current users, NICT has also developed empirical models for space weather forecasting. These types of models can provide practical information in near real time. Operational forecasting models for the Dst index using neural network techniques have been developed [Watanabe et al., 2003]. Recently, NICT has developed a prediction model for relativistic electron flux at GEO using Kalman filter based on multivariate autoregressive model [Sakaguchi et al., 2013]. The development of prediction models for the am index are also planned based on the results obtained from Nagatsuma . These results suggest that in addition to solar wind–magnetosphere–ionosphere coupling, the current condition of ionospheric conductivity driven by solar EUV is also important for predicting geomagnetic disturbances.
Since the Japanese space weather forecast center belongs to a research organization, not only operational service but also cutting-edge research and development are essential. To improve future operational space weather forecast, NICT is focusing on the following two major subjects during the 5 year plan 2011–2015.
Predictions of space environment around GEO.
Predictions of equatorial ionospheric disturbances.
The subject of topic 1 is to predict the keV-MeV particle fluxes in GEO for operational satellite, because satellite charging due to substorms and relativistic electron enhancements are major causes of satellite malfunctions. For this purpose, NICT is developing both empirical and numerical models for predicting relativistic electron enhancements and a high-precision global MHD simulation code for predicting the timing of substorm particle injections.
The subject of topic 2 is to predict equatorial ionospheric disturbances with 1 h lead times for satellite telecommunication, navigation, and positioning. For this purpose, NICT is developing a near–real-time prediction system for the generation and propagation of equatorial plasma bubbles, as well as a high-precision ionospheric simulation code including atmospheric and magnetospheric interactions.
In terms of regional relationships, recently, NICT has established the Asia-Oceania Space Weather Alliance (AOSWA) that includes several organizations in the Asia-Oceania region who are interested in space weather forecasting. The office of AOSWA is operated by NICT (http://aoswa.nict.go.jp/). The main objective of AOSWA is to construct a regional linkage of space weather information for operations and research. The first AOSWA workshop was held in Chiang Mai, Thailand, in 2012. Activities for space research and development are growing in the Asia-Oceania region. This means that the importance of space weather forecasting is becoming more recognized in the region. Thus, a strong regional link for enhancing space weather forecast activities is being constructed.
Tsutomu Nagatsuma is a research manager of Space Weather and Environment Informatics Laboratory, Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology (NICT). Email: firstname.lastname@example.org.