(dī ur’ n∂ls) Phenomena with a periodicity of about one day. Changes in the geomagnetic field related principally to the rotation of the Earth in the magnetosphere (q.v.) and also involving amplitude and phase variations with season and latitude (by as much as 100 nT); records from a stationary magnetometer are used for their removal. Average daily changes in radio-wave propagation because of diurnal changes in the ionosphere affect radio-positioning systems. Published tables allow one to correct for major skywave variations with systems like Omega, but unpredictable local skywave variations and sun-spot effects remain.