Determining ULF wave contributions to geomagnetically induced currents: The important role of sampling rate

Past studies found that large-amplitude geomagnetically induced current (GIC) related to magnetospheric Ultra Low Frequency (ULF) waves tend to be associated with periods >120 s at magnetic latitudes >60°, with comparatively (a) smaller GIC amplitudes at lower latitudes and shorter wave periods and (b) fewer reports of waves associated with GIC at lower latitudes. ULF wave periods generally decrease with decreasing latitude; thus, we examine whether these trends might be due, in part, to the undersampling of ULF wave fields in commonly available measurements with 60 s sampling intervals. We use geomagnetic field (B), geoelectric field (E), and GIC measurements with 0.5–10 s sampling intervals during the 29–31 October 2003 geomagnetic storm to show that waves with periods