History of Kakioka Magnetic Observatory

Abstract. Kakioka Magnetic Observatory (KMO) was founded in 1913 by Central Meteorological Observatory (CMO, later Japan Meteorological Agency) as a successor of Tokyo Magnetic Observatory. Kakioka was a village 70 km north of Tokyo and was selected to escape from tram noise at Tokyo. At first, it was an unmanned observatory only for the geomagnetic field observation. Then, the Great Kanto Earthquake in 1923 changed the fate of KMO because the earthquake severely damaged CMO at Tokyo and recording papers of KMO were lost. KMO was manned in 1924 and was redesigned as an institute for geophysics rather than geomagnetism. KMO operated a variety of observations such as the atmospheric electric field, the geoelectric field, the seismicity, the air temperature, the wind velocity, the sunspot and solar prominence as well as the geomagnetic field by 1940’s. In addition, research activity flourished with the leadership of the first director Shuichi Imamichi. After the World War II was over in 1945, KMO formed a network of observatories in Japan by founding several branch observatories originally for the geoelectric field observation. Two branch observatories at Memambetsu and Kanoya survived with the geomagnetic field observation added in the International Geophysical Year project (1957–1958). Efforts on development of instruments for the geomagnetic absolute measurement and systems of high sampling recordings in 1950’ to 1970’s resulted in the development of Kakioka Automatic Standard Magnetometer (KASMMER) system in 1972. KASMMER measured the geomagnetic field every three seconds at the highest standard in the world in a digital form giving 1 minute digital values of the geomagnetic field available. Those system has been updated and the high sampling technology was applied to the geoelectric field observation and the atmospheric electric field observation. Later adding the geomagnetic field observation at Chichijima in 1971, KMO established the unique electric and magnetic observation network at Kakioka, Memambetsu, Kanoya and Chichijima and provided precise and high-speed sampling data (1 min, 1 sec, and 0.1 sec values) by 2001. On the other hand, KMO gradually terminated or automated their observations and reduced their staff for last several decades following the government’s reform policy. The two branch observatories at Memambetsu and Kanoy were unmanned in 2011 and the atmospheric electric field at Memambetsu was terminated at that time. The geoelectric field observations at Kakioka, Memambetsu and Kanoya were terminated in 2021 as well as the atmospheric electric field at Kakioka. KMO focus the geomagnetic observation for now and put efforts to the total force observation at volcanos and the digitization of historic analogue data.