The Conrad Observatory will continue a long history of measurements of magnetic field variations in Austria with a yet unmatched precision.

Earth's magnetic field originates from dynamo processes within the core (Fig. 1). It constitutes a protective shield against cosmic and solar radiation. The geomagnetic field, however, is not constant but experiences continuous variations on various time scales ranging from seconds to million of years. Short term variations like daily magnetic field variations and geomagnetic storms are mainly related to interactions of solar wind with the Earth's magnetosphere, producing external field variations. Internal field variations, due to processes in the Earth's dynamo, cause long term field variations primarily. Complete reversal of the magnetic field is the most prominent member of these variations. During field reversals the whole magnetic field of the Earth changes polarity and field strength is  reduced by more than 90%. In Earth's geological history such reversals happened quite frequently, although the last reversal was approximately 780,000 years ago.


For approximately 170 years geomagnetic field variations have been recorded by globally distributed observatories. Some of the oldest preserved geomagnetic measurements in Austria date back to the middle of the 18th century and were recorded at Kremsmünster Abbey. Regular recordings started in 1832 followed by the installation of a geomagnetic observatory in 1839. In contrast, official observations started as early as the 1850s after the foundation of the "k.k. Centralanstalt für Meteorlogie und Erdmagnetismus", today known as the ZAMG.

The first director of the Centralanstalt, Karl Kreil, conducted a geomagnetic survey for the Austrian Empire. This survey included the countries of the Austrian Empire, southern Europe, the coast of the Adriatic Sea, Anatolia (Asia Minor), and the Black Sea. Results were summarized in geomagnetic maps of the era 1850.0 and served as a baseline for navigation using compasses and starting point for geomagnetic research in Austria. Since then, five more geomagnetic surveys have been conducted in Austria summarized in geomagnetic maps for the era 1890.0, 1930.0, 1960.0, 1970.0 and most recently 1997.0, as well as one aeromagnetic survey (1977–1982). All geomagnetic surveys need reference measurements of absolute values of Earth's magnetic field, which are provided by geomagnetic observatories.

The k.k. Centralanstalt established its first geomagnetic station in 1852 in Vienna (k.k. Theresianum) observing declination, inclination and intensity. Magnetic field observations over the last 170 years point to some peculiarities of the magnetic field and its variations. The global field strength dropped by more than 10% in this time. Additionally, the direction of the magnetic field changed considerably, e.g. more than 20° change of declination in Austria. In particular the strong drop of field strength has been interpreted as a first indication of an upcoming field reversal. In order to provide present magnetic field values in Austria, repeated magnetic surveys have been performed annually across the country since the late 1990s. Subsequently, the Austrian Geomagnetic Service publishes annual geomagnetic maps.

In 2013 the Conrad Observatory (Trafelberg, NÖ) will take over as the main geomagnetic station in Austria from the long-serving station in Vienna (Cobenzl, since 1954). Magnetic recording takes place in underground tunnels to maintain exceptional temperature stability. Observatory data provides geomagnetic reference values and serves reduction purposes.

Snap shot during the last field reversal according to IMMAB4.

Geomagnetism comprises several additional subjects:

1) space weather/climate:
interaction between solar wind and magnetosphere

2) paleomagnetism:
past geomagnetic field variations and their effect on Earth, including investigations of tectonic conditions and plate reconstruction by field records, characteristics of geomagnetic field reversals and excursions (Fig. 2), dating by magnetostratigraphy, etc.

3) archeomagnetism:
historic field variations

4) biomagnetism:
interaction between organism and magnetic field

 

Magnetotactic bacteria in a water drop under the optical microscope. The white line in the upper left corner gives the direction of the magnetic field, which determines the swimming direction (© Ramon Egli)

References
Leonhardt, R., and Fabian, K. (2007): Paleomagnetic reconstruction of the global geomagnetic field evolution during the Matuyama/Brunhes transition: Iterative Bayesian inversion and independent verification. Earth Planet. Sci. Lett., 253, 172-195.
Josef Berger, Gerald Duma, Barbara Leichter (2010) Magnetic repeat station surveys in Austria. COBS Journal 2010. (link)
Josef Berger, Norbert Blaumoser, Gerald Duma, Barbara Leichter (2001) Geomagnetische Landesaufnahme in Österreich. In: Christa Hammerl, Wolfgang Lenhardt, Reinhold Steinacker, Peter Steinhauser (Hrsg.): Die Zentralanstalt für Meteorologie und Geodynamik 1851 – 2001. Leykam.
P. Augustin Reslhuber (1884) Über das Magnetische Observatorium in Kremsmünster und die aus den Beobachtungen bis zum Schlusse des Jahres 1850 gewonnenen Resultate. Bericht an die k.k. Centralanstalt für Meteorlogie und Erdmagnetismus, Wien.

Related Literature
Kreil, K. (1848, 1849, 1850, 1851, 1852) Magnetische und geographische Ortsbestimmung im österreichischen Kaiserstaate 1856, 1847, 1848, 1850, 1851. Erster bis Fünfter Jahrgang, Prag, k.k. Hofdruckerei.
Toperczer, M. (1956) Das geophysikalische Observatorium Wien-Kobenzl. Arch.Met.Geoph, Bd.9, 3. Heft, Springer Verlag in Wien.

Suggested Literature
Our Magnetic Earth – The Science of Geomagnetism (2010) Ronald T. Merrill, 261 S., University of Chicago Press.
Introduction to Geomagnetic Fields, W. H. (2003) Campbell, 337 S., Cambridge University Press.

Suggested Online Material
Paleomagnetism: Magnetic Domains to Geologic Terrances” by Robert F. Butler (1992)
NOAA Magnetic Field Calculator
ZAMG Geophysik Magnetik: additional information on geomagnetic observatories and surveys, etc. (German only)

Definitions
Geomagnetic surveys conduct measurements of the geomagnetic field at numerous locations across the country. Various geomagnetic components are determined and used to produce accurate maps. Since the geomagnetic field is changing over long periods of time, geomagnetic surveys need to be repeated regularly - ideally every ten to twenty years.

Geomagnetic observatories are scientific institutions serving the primary task of measuring the geomagnetic field at the planet's surface, observe secular variations of Earth's main field and temporal variations of the field, which are often caused by ionospheric current systems. All of these task need to be performed constantly with uninterrupted registration.