A La Cour magnetometer was first deployed at Halley in 1957 as a contribution to the International Geophysical Year, and a magnetometer has been operating there ever since. There are many difficulties associated with making measurements on a moving ice-shelf, and especially in a regime where the magnetometer housing becomes buried deep below the snow's surface (Simmons and Rouse, 1984). The position of the observatory is determined from a satellite navigation system; the station is currently moving westwards at approximately 700 m per year. As a consequence, no absolute measurements are made, and the station currently operates as a variometer station utilising an EDA fluxgate magnetometer. The H, D and Z components of the Earth's magnetic field are digitally sampled once every second with a resolution of ~1 nT.

The magnetometer data are used in support of all geospace studies at Halley. In the past, they have been used only occasionally as the principal data-set to investigate geospace processes, e.g. for determining the effects of the y-component of the interplanetary magnetic field on the ionospheric current systems on the night-side (Rodger et al., 1984) and the dayside ( Rodger and Cowley, 1986). This limitation, imposed by the isolation of the instrument, has now been removed with the introduction of a growing network of magnetometers on the multi-national array of AGOs. This network will allow a wide variety of research of the type already demonstrated by the exploitation of data from CANOPUS, SAMNET, MACCS, the EISCAT Cross, the Greenland chain and other magnetometer arrays, to be carried out.

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