The geomagnetic data of the Clementinum observatory in Prague since 1839

Abstract

Abstract. The historical magnetic observatory Clementinum operated in Prague from 1839 to 1926. The data from the yearbooks that recorded the observations at Clementinum have recently been digitized and were subsequently converted, in this work, into the physical units of the International System of Units (SI). Introducing a database of geomagnetic data from this historical source is a part of our paper. Some controversial data are also analysed here. In the original historical sources, we identified an error in using the physical units. It was probably introduced by the observers determining the temperature coefficient of the bifilar apparatus. By recalculating the values ​​in the records, some missing values ​​are added; for instance, the temperature coefficients for the bifilar magnetometer, the baselines, and the annual averages for the horizontal intensity in the first years of observations were redetermined. The values ​​of absolute measurements of the declination in 1852, which could not be found in the original sources, were also estimated. The main contribution of this article rests in critically reviewed information about the magnetic observations in Prague, which is, so far, more complete than any other. The work also contributes to the space weather topic by revealing a record of the now almost forgotten magnetic disturbance of 3 September 1839.

Magnetic storm and term‐day observations at the Prague observatory Clementinum in the mid‐19th century

“…The importance of these data is all the greater because in geomagnetic disturbances, it is necessary to study both their global and local manifestations. Two of the storms in our database observed at the Clementinum Observatory have already been the subject of research (Hejda et al, 2021;Valach et al, 2019). Several other unique records in the database also have the potential to contribute to better understanding of the mechanisms of strong geomagnetic disturbances.…”

“…The problem with the above‐described method of observing variations ∆H was especially due to the temperature dependence of the magnetization of the rod, which entered into the calculation of the magnetic force that was trying to turn the magnet north–south (Hejda et al, 2021; Nevanlinna, 1997). This effect, expressed by an additional coefficient k T , had to be included in the resulting equationwhere h is the deflection of the rod in the horizontal direction with respect to a reference value h 0 (both h and h 0 are listed in tables within the yearbooks and are expressed in parts of the scale, i.e.…”

“…The data from 1839 to 1871 were published in instrumental scale units and had to be converted to the physical units of the International System of Units (SI). The regular daily observations have already been digitized and processed (Hejda et al, 2021).…”

“…In the following, we will describe the structure of our data, explain the methodology of selecting the presented events and briefly outline the procedure for converting raw data to physical units (a more detailed description of the procedure can be found in Hejda et al (2021)).…”

Historical geomagnetic observations from Prague Observatory (since 1839) and their contribution to geomagnetic research

“…We also report on the beginnings of the magnetic survey in Bohemia. More detailed information concerning the whole time span of geomagnetic observations at Clementinum can be found in Hejda et al (2021a). The historical records of strong magnetic disturbances and term-day observations at Clementinum are discussed in Hejda et al (2022) and comprehensive online databases are provided by Hejda et al (2021b) at https://doi.org/10.1594/PANGAEA.936921.…”