ULF/lower‐ELF electromagnetic field measurements in the polar caps

A review is given of the known properties of naturally occurring ULF/lower‐ELF (0.022–100 Hz) electromagnetic pulsations in the polar caps. Because polar cap measurements by Western scientists in this particular frequency range have been surprisingly limited (even when allowance is made for the logistical difficulties), emphasis is given in the review (1) to a description of the gaps in our knowledge of the properties of the pulsations and (2) to the uniqueness of the geomagnetic field configuration in the polar caps and its implications. Given the gaps in knowledge and the unique field configuration, the opportunities for innovative research on ULF/lower‐ELF electromagnetic pulsations in the polar caps appear to be particularly promising.