Geomagnetic monitoring at Davis

Graph detailing Earth's X, Y and Z magnetic field components at Davis station.
Graph showing fluctuations in the earth's magnetic field at Davis. The fluctuations maximise at around noon and midnight due to magnetic field interactions with solar wind and auroral substorms, respectively.
Graph detailing ionospheric opacity at Davis station.The riometer at Davis. The two single rod-like antennas at the top do the work. The structure underneath is a ground plane to ensure the antennas are in the right ‘environment’.

The Earth’s magnetic field at Davis

At Davis, Antarctica, (and Casey) we measure the north (X), east (Y) and vertical (Z) components of the Earth’s magnetic field (see first picture). The major component of the magnetic field is generated by currents in the Earth’s core. This amounts to approximately 54,000 nT (nanotesla) at Davis.

Currents flowing in the upper atmosphere at around 120 km result in variations that may amount to some 2% of the total field, but are typically much smaller. At Davis the fluctuations are maximised broadly around noon (~10 UT) and near midnight (~12 UT). The noon fluctuations result from currents associated with the interaction of the solar wind and the sunward extremity of the Earth’s field. Davis is ideally located for studying this interaction. The midnight fluctuations result from currents associated with auroral intensifications (auroral substorms). The sharp onsets shown are typical of auroral substorms. The variations depicted amount to some 800 nT in magnitude.

Our measurements of the magnetic field are transferred to the Space Weather Services section of the Bureau of Meteorology for use in ionospheric forecasting, and to world data centres. The latest observations from Davis and Casey can be found on the Bureau of Meteorology website.

Ionospheric opacity

A riometer (relative ionospheric opacity meter) is essentially a wide-angle radio telescope that is used for studying the aurora. It measures the combined signals at 30 MHz of the radio stars in its wide (60 degree) vertically oriented beam. The gentle curve on the day’s data (see second picture) results from the passage of the Milky Way over the Davis site.

When energetic electrons associated with aurora impact the upper atmosphere they may ionise the atmosphere significantly at lower altitudes (around 90 km) than normal. This low altitude ionisation absorbs some of the signal from the stars in the riometer beam. This results in the ‘bights’ out of the smooth varying curve at around 2030 UT and 2130 UT. A comparison with the Davis magnetic data (first picture) shows the riometer events are associated with current intensifications at this time.

Riometers allow the study of energetic auroral events, independent of cloud cover at the site. The Davis riometer is one of four operated through the Australian Antarctic program. Data from these riometers are regularly transferred to the Space Weather Services section of the Bureau of Meteorology for use in ionospheric forecasting, and to world data centres. View the latest results on the Bureau website.