Formation of sporadic E-layers by magnetospheric electric fields in the southern polar cap ionosphere

The occurrence of ionospheric electric fields and sporadic E ( Es)-layers were measured with a modern, HF digital ionosonde located at Casey, Antarctica (81°S, corrected geomagnetic latitude) during the late austral summer of 1995/96. The observations show that Es-layers had a peak occurrence near to magnetic midnight under the influence of south-west electric fields generated by the solar wind-magnetosphere interaction. Our results are consistent with the standard theory of thin Es-layer formation by electric fields applied to the southern hemisphere, and they complement the basic prediction that north-west electric fields will produce thin Es layers at high latitudes in the northern hemisphere. Hence the magnitude and orientation of the interplanetary magnetic field must be a major factor in the control of Es-occurrence at high latitudes.