The daily variations of the vertical (Z) element of the geomagnetic field around the coast of mainland Australia

Abstract

Use is made of an array of magnetic stations spread across the Australian mainland to examine the daily variation of the vertical element Z of the magnetic field. On sections of the west and east coasts visual inspection of Z variations shows that they respond mainly to the onshore component of the horizontal field as predicted by Bennett and Lilley, though only south of about 22°S on the east coast and south of 20°S on the west coast. On the north and south coasts this “coast effect” is not clearly seen at periods corresponding to the daily variation, though it sometimes appears on shorter time scales. On the north and south coasts Z appears to be mainly controlled by the decrease with latitude of the overhead eastward ionospheric currents as measured by the latitude gradient in the northward field, X. By subtracting the vector Z variation at an inland station from Z at a coastal station, the anomalous coastal effect in Z is calculated at periods of 12 and 24 h. These data show that the coastal effect is not just related to the horizontal onshore component but that some phase change is also required. An increase with latitude of the overhead eastward currents is sometimes found in morning hours corresponding to the morning current system identified in earlier work.