AVAILABILITY AND ACCESS TO DATA FROM KAKIOKA MAGNETIC OBSERVATORY , JAPAN

The Japan Meteorological Agency (JMA) is operating four geomagnetic observatories in Japan. Kakioka Magnetic Observatory (KMO), commissioned in 1913, is the oldest. The hourly records at KMO cover over almost 100 years. KMO is JMA’s headquarters for geomagnetic and geoelectric observations. Almost all data are available at the KMO website free of charge for researchers. KMO and two other observatories have been certified as INTERMAGNET observatories, and quasi-real-time geomagnetic data from them are available at the INTERMAGNET website.


INTRODUCTION
The Japan Meteorological Agency (JMA) operates four geomagnetic observatories in Japan (Table 1, Fig. 1).Kakioka Magnetic Observatory (KMO) is JMA's headquarters for geomagnetic and geoelectric observations.KMO has made data from the three observatories on the main Japanese islands, covering geomagnetic latitudes from 20° to 35°, available to researchers.Three of these observatories are part of the INTERMAGNET global network.KMO was commissioned in 1913, 70 km northeast of Tokyo, to replace the Tokyo geomagnetic observatory, which suffered from severe noise after construction of the Tokyo train system.The hourly geomagnetic field data recorded at Kakioka cover almost 100 years.This paper describes the geomagnetic and geoelectric data available from JMA and provides information on how to access them.

A BRIEF HISTORY OF GEOMAGNETIC DATA RECORDED IN JAPAN
JMA has published geomagnetic data since 1896 (Kakioka Magnetic Observatory 1983).Until 1912, geomagnetic field observations were carried out at Edo-jo Castle in the very center of Tokyo.Because of its central city location, contamination of geomagnetic data by artificial noise became a problem.A plan to introduce a city tram service close to the site forced the observatory to be moved away from Tokyo (Toya et al., 2005).
The main reason for the choice of the new site was to avoid areas where electric train systems were likely to be commissioned.Consequently, the new observatory was located in the remote rural area of Kakioka.Because there was originally only one permanent staff member on location at the new site, officers from the Central Meteorological Observatory (CMO) in Tokyo were sent monthly to Kakioka to take absolute geomagnetic measurements.Data recorded on bromide paper and field notes were taken back to CMO.
The great Kanto earthquake struck the Kanto Plain on the Japanese main island of Honsyu on Saturday, 1 September 1923.The fire that followed devastated Tokyo and inflicted severe damage on the CMO buildings.Almost all of the data from Kakioka for the period from January 1917 to August 1923 were destroyed by the fire.
The earthquake caused severe damage to KMO.Though temporary repairs had been made by January 1924, the facilities remained inadequate.CMO rebuilt the KMO office and other buildings and installed new magnetic observation systems.All of the staff involved in geomagnetic observation were then stationed at Kakioka, allowing swift processing of data.Absolute measurements were routinely conducted at a higher frequency, changing from monthly to weekly.Geomagnetic data from KMO have provided a continuous record since 1913, even covering the period of World War II.
KMO branch observatories were established at Memambetsu (MMB) in 1952 and at Kanoya (KNY) in 1958 (Fig. 1), in response to the International Geophysical Year campaign.Geomagnetic data have been recorded at an automated station at Chichijima (CBI) in the Ogasawara Islands since 1973.Figure 2 shows the historical variations of the geomagnetic field recorded at these four observatories.
The main components of this instrument are optical pumping magnetometers, a proton precession magnetometer, an angle measuring instrument, and a computer processor for making calculations.Operation of all of these components, except the angle measuring instrument, is automated.The installation of KASMMER allows KMO to provide data at one-minute resolution.KMO commenced recording one-second in 1983 (Tsunomura et al., 1994) and 0.1-second data in 1997 (Oowada et al., 2003), respectively.Similar systems with one-second and 0.1-second resolution have since been installed at MMB and KNY.

Table 1 .
Geographic 1 and geomagnetic 2 coordinates and altitudes of magnetic observatories operated by JMA 2 11th International Geomagnetic Reference Field