Morning quiet-time ionospheric current reversal at mid to high latitudes

The records of an array of magnetometers set up across the Australian mainland are examined. In addition to a well-defined current whorl corresponding to the ionospheric S-q current system, another system of eastward flowing currents is often found in the early morning. The system is most easily identified at observatories poleward of the focus of the Sq system, where a morning reversal from eastward to westward currents can be seen. The time of the reversal is usually later, sometimes up to 12 h local noon, in June (Southern Winter) than in other seasons. There is some evidence of a similar current system at other longitudes and in the Northern Hemisphere. An important outcome of the study is that it enables identification of which features of a daily variation of the northward magnetic field Delta X relate to an Sq current whorl and which must be attributed to some other current system.