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Introduction

The Japan Meteorological Agency (JMA) conducts continuous observation to accurately monitor variations of geomagnetic field originating in the Earth's interior and exterior. The resulting data support geological surveying/research, environmental monitoring of the solar-terrestrial system, space weather forecasting, aviation/maritime safety, warnings of radio communication issues, and assessment of volcanic activity. For monitoring of this natural magnetic phenomenon, ongoing observation is needed with precise and stable instruments at locations where geomagnetic fields are unaffected by anthropogenic disturbances. Also, the operation of a global observation network with international cooperation is essential.

Kakioka Magnetic Observatory

Stationary magnetic observation in Japan began in Akasaka, Tokyo, during the First International Polar Year (1882-1883), and was moved to Kakioka in Ishioka (Ibaraki Prefecture) in January 1913. The observatory is an auxiliary institution of JMA for monitoring and analysis of geomagnetism and geoelectricity. The main observatory in Kakioka is complemented by branch observatories in Memambetsu (Hokkaido) and Kanoya (Kagoshima). Another magnetic station is operated on Chichijima Island (Ogasawara, Tokyo). These four facilities conduct regular observation of geomagnetic fields in collaboration with other observatories worldwide.

Kakioka Automatic Standard Magnetometer (KASMMER)
geomagnetic observation system

The unique data produced by the observatory significantly support surveying and research in the development of magnetic monitoring equipment, observation techniques, aeronomic phenomenon analysis and volcanic activity evaluation. They are used for societal purposes as well, such as forecasting of radio communication failure and magnetic cartography. Kakioka was designated in 1973 as one of four magnetic observatories worldwide producing data used to determine Dst index values representing the intensity of equatorial ring currents surrounding the Earth. It is the only Japanese institution authorized to certify magnetic instruments. Staff have been dispatched numerous times for wintertime observation of auroras and other phenomena in Antarctica.

Observatory location

Magnetic observation in Kakioka began in 1913 after discontinuation by the Central Meteorological Observatory (the predecessor of JMA) in Tokyo due to interference from the new direct-current urban tram service. The renowned physicist Torahiko Terada played a major role in the identification of this site as a suitable location. Magnetic observation there has continued ever since, even during wartime periods. The precise data produced are widely recognized internationally, and represent a highly valuable resource for humanity in general. The observatory site — largely isolated to prevent interference from man-made noise — features buildings constructed over a century ago, and has a rich natural environment with Japanese dandelions and other flora.

1. Main House (Office Building I) Constructed in 1925, this symmetrical German-style building has Western-style roof tiles and decorative eaves. It was designed so that Mt. Tsukuba can be viewed directly from the main entrance.
2. KASMMER Geomagnetic Observation Facility The facility was established at the Kakioka site in 1972 for accurate and stable geomagnetic observation and digital recording.
3. Atmospheric Electricity House Atmospheric electrical field fluctuations (ave. 100 V/m) were observed here until 2021. The building was constructed in 1925.
4. Laboratory Constructed in 1924, this brick structure has a copper shingle roof and copper gutters, as no iron or other magnetic materials can be used in magnetic observation facilities. The outdoor light above the facade has a stained-glass window in the shape of a beech tree. The tiles below the windows and the pillars on both sides of the front feature floral decorations.
5. Stone Chamber (Variometer House I) Built in 1912, the main body of the structure features a D-shaped stone design and earthen banking for temperature stabilization. Its old-fashioned thatched roof was replaced with slate in 1961.
6. Tulip and Platanus trees Both these trees are protected under designation by the local Ishioka authorities. Belonging to the magnolia family, the tulip tree is 26 m tall and around 90 years old. Its light-yellow/green tulip-shaped flowers bloom in early summer.