Teoloyucan Magnetic Observatory

More than one Century of magnetic observations.
The magnetic observations in México come from the end of the XVIII century. They were done by Antonio Alzate and Alejandro von Humbolt and in the beegining of the XIX century, by the School of Mines. The first formal magnetic observatory was installed in Palacio Nacional in 1879 inside the Meteorological and Magnetic Central Observatory. It was working with the Tompson magnetometer (H and D), and with a Negretti-Zambra compass (I). The observatory was working until May 1877 because of modifications in to the building that sheltered it.
During April 1889 was installed a bench in the Tacubaya Astronomical Observatory for magnetic observations with an Elliot-Dover magnetometer (H and D), a Negretti-Zambra compass (I) and a set of continous reception Carpentier variographers. In 1902, with the instalation of electric railways the bench had to be closed.
In 1903 the equipment was moved to Cuajimalpa town, however, in 1911 it was moved again becuase the electric railways got close to that place. The new observatory was installed next to the Municipal Building from Teoloyucan, 36 km northward México City. It was working with the same equipment of Cuajimalpa. In 1921, the observatory get Mascart variographers, a Dover magnetometer, a Edelman galvanometer, and a magnetic balance. In 1929, it was a C.I.W. magnetometer and in 1931, the Eschenhagen-Askania variographers (D, H, and Z). In 1949, with the foundation of Geophysics Institute, the observatory become to be part of it.
A remodelation in the structure of the Municipal Building in 1978 disturbaced the measurements, and the observatory was moved again. For the new location it was considered the period of magnetic observations measured in that place. So the new place was selected next to the Municipal Cemetery in the limits of the town, it is working with the same continous reception classic equipment and also with QHM magnetometers, Geometrics PPM, and Ruska, such magnetometers are working currently.
Since July, 1996 it is working two digital equipments. These were installed during the Latin-American Workshop on Geomagnetic Instruments (ELIG 96). The first one was designed and made by Dr. Jean Rasson and Teotonio Ferreira in the Observatoire Magnétique de Dourbes (Royal Meteorological Institute) , Belgium. This is a DI-flux magnetometer modified from a RUSKA nonmagnetic theodolite for absolute measurements, and a two components fluxgate variograph (DI, it is called LAMA). Both are working with a PPM Geometrics G856.
The second one is a three component fluxgate variograph FGE (DHZ, it is called DMI). This last equipment belong to the Danish Meteorological Institute, and was installed by Dr. Ole Rassmussen to work for a two years period in TEO.
Both, LAMA and DMI, are coneccted to the same data adquisition system, and they get magnetic values each minute. In the future, these magnetic values will be available in real-time through INTERMAGNET.

Calibrations.
Three calibrations have been done in Teoloyucan for the classic equipment. The first one was in 1954 when the variogrphers were sent to the U. S. Coast and Geodetic Survey (now the U. S. Defense Mapping Agency), for the instalation of temperature compensating magnets. During 1971 and 1972 a second calibration was carried out in the observatory with instruments from Inter-American Geodetic Survey (IAGS, that doesn't exist anymore). And the last one was in 1991 helped by the Pan-American Institute of Geography and History (PAIGH) with equipment of the Observatório Nacional do Brasil.

Magnetic Values in Teoloyucan.
The Geophysics Institute has published since 1950 the values for the magnetic components D, H, and Z in Teoloyucan, they were interrupted during 1978 becuase the change of observatory site. The publication of values since that date is in processing now, and it will be ready about next months. It is aviable in ftp the table with yearly mean values 1914-1994, the monthly mean values 1923-1990, as well as published years 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, and 1990.

Mean Hourly and Monthly Values
Monthly Mean Values
Yearly Mean Values

Inquires, correspondence:
geomagne@tonatiuh.igeofcu.unam.mx

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