Daily Variation of Total Magnetic Field over the British Isles

Abstract

THE use of observatory data as a basis for the correction of diurnal variation in magnetic surveys is common both for secular repeat stations spread over a wide area, and in ground and marine magnetic surveys where limitations of personnel and equipment prohibit the maintenance of a local base. Geographical interpolation of the variations is usually based on local time and latitude, the errors involved in this procedure being assumed to be small. In 1918, Walker¹ stated that such interpolation was incorrect, although he was prevented by the First World War from carrying out investigations to provide a more rigorous alternative. So far as I am aware, the situation today is little changed, at least in the British Isles.