Geomagnetic pulsations associated with the polar cusp have been detected at Cape Parry, Northwest Territories, Canada, using flux gate and induction magnetometers. Data from this station show enhanced power almost every day near local noon. It is this enhancement which is taken as the signature of the polar cusp. Maximum signal levels are observed prior to local noon, although the signals are present for several hours on each side of local noon. The spectrum of pulsations near the cusp is broadband, reaching from a few millihertz to above 1 Hz. On average the power spectrum decreases with frequency as f−2.6. Within this general decrease there are often found regions of enhanced power, principally near 5 mHz and near 40 mHz. We have identified the 5-mHz band with fluctuations in ionospheric currents associated with the cusp boundary and its motions. The 40-mHz band is presumed to be due to direct penetration of the hydromagnetic radiation in the cusp to the ground. From the measured spectrum we infer an rms fluctuation amplitude of the cusp currents of approximately 3×10³ A, and from this we estimate the total power dissipated by these fluctuations of approximately 4×107 W.

ULF signatures of the polar cusp

A study of concurrent magnetic field and particle precipitation pulsations, 0.005 to 0.5 Hz, recorded near College, Alaska

High-latitude ULF waves at all frequencies are reviewed with emphasis on simultaneous measurements in both hemispheres. The seasonal variation of interhemisphere high-latitude data is valuable in helping to understand the topology of the magnetosphere. The frequent occurance of Pc 1–2 pulsations at high latitudes and in the polar cap is discussed. Evidence for ground detection of flux transfer events via magnetic pulsations is reviewed. The correlation of high-latitude pulsation data with other ground techniques of measuring particle precipitation is presented to better define the subset of high-latitude ULF that is produced by local current systems fed by particle precipitation and field-aligned currents. Finally, simultaneous ground and spacecraft measurements of ULF are reviewed which provide information on the propagation of ULF across such boundaries as the magnetopause and the ionosphere.

Review of hydromagnetic wave studies in the antarctic

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.

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

Amplitude and polarization measurements of structured Pc 1 micropulsations obtained in Alaska and in Finland imply that the Pc 1 source lines are near or inside the plasmapause. The measurements give the source lines significantly closer to the earth than are given by Pc 1 dispersion calculations. Specific Pc 1 events are compared with plasmapause positions determined by the Ogo 3 and Ogo 5 satellites. We present some evidence that implies that structured Pc 1 source lines corotate with the earth.

V.P. Hessler

Papers

The 2-0.1 Hz polar cap micropulsation activity