We present magnetic field data from the cusp‐latitude South Pole station that exhibit, under appropriate local time and interplanetary magnetic field conditions, the signature expected in the ionosphere from a flux transfer event (FTE) at the magnetopause. In particular, the model of multiple X‐line reconnection at the magnetopause predicts field‐aligned currents in helical flux tubes, with transverse magnetic fields propagating as Alfvén waves toward the ionosphere. The distinctive magnetic signature at a polar cap magnetic station, particularly in the vertical component, can be used to infer the signs of the By and Bz components of the interplanetary magnetic field.

Magnetic field data acquired at high‐latitude, near‐conjugate stations (Iqaluit, Northwest Territories, Canada, and South Pole Station, Antarctica) are studied in order to examine in more detail the nature of magnetic “impulse” signatures that occur in the data and that are produced by ionosphere currents which are caused by magnetopause processes. An examination of the data, both visually and with a computer algorithm “detector,” from the 5‐month interval July–November 1985 found many such magnetic “impulse” events which could be interpreted in terms of intense field‐aligned currents above the observing stations. All the events have a half‐width in time of a few minutes, and most are reasonably conjugate. The majority of the events studied have magnetic field perturbations in the vertical component which can be interpreted in terms of field‐aligned currents directed in the same direction (either into or out of the ionosphere) in both hemispheres. The perturbations in the horizontal plane are consistent with an interpretation in terms of a single cycle of an odd mode Alfvén wave. For the events shown in detail in this paper, the impulsive magnetic signatures are found to occur for the interplanetary magnetic field BZ component positive, negative, or variable. The observations are discussed in the context of some contemporary ideas on the generation of ionospheric disturbances by magnetopause processes such as sporadic reconnection (“flux transfer events”), plasma injections into the low‐latitude boundary layer, Kelvin‐Helmholtz instability, and solar wind “pressure pulses.” Near‐equatorial data from a location in the same local time section as the high‐latitude data are used to show the gross differences in global ionospheric currents stimulated by sudden commencements and by the magnetic impulse events.

Measurements of the cable power supply voltage at the North American end of the fiber optic transatlantic telecommunications cable TAT‐8 during the March 1989 magnetic storm has provided a measure of the large scale changes in the total Earth potential across the Atlantic during the storm interval. East‐west potential changes as large as 700 volts (∼0.12 volts/km) peak‐to‐peak were observed, with many smaller amplitude variations also seen. The largest variations in Earth potential occurred during an extended interval of a very intense eastward electrojet as measured by a magnetometer at the North American terminus of the cable. The eastward electrojet current probably exceeded 106 amps. The design of the TAT‐8 cable power feed equipment is sufficiently conservative that even such unusually large Earth potentials as those measured during this storm were not a threat to the integrity of the communications system.

A special campaign was conducted at the Sondre Stromfjord incoherent scatter radar facility in October 1985 to study hydromagnetic and atmospheric gravity wave phenomena near the cusp regions of the magnetosphere. During a day when the convection reversal boundary was measured just to the north of the radar, a field‐aligned current filament of inferred amplitude ∼2 × 105 A was measured at the boundary. Both ion and electron heating appeared to accompany the current filament. Magnetic field data acquired in the southern conjugate hemisphere are used to conclude that the current filament was probably on closed field lines. The current filament may be evidence of the magnetosphere boundary layer on closed field lines, perhaps produced by the injection of magnetosheath plasmoids onto the field lines by a flux transfer‐type reconnection process.

A field campaign, using three magnetometer stations spaced in latitude around the equatorial magnetic field distance L ∼ 1.9, was conducted in early 1979 to investigate the polarization characteristics of hydromagnetic waves at low geomagnetic latitudes. The magnetic pulsations are observed to have periods in the range ∼20‐25 s and to occur primarily in the local morning hours. Statistically, the polarizations at all three stations were predominantly left handed in the local morning hours and right handed in the local afternoon. At the highest‐latitude station (L ∼ 2) the orientation of the major axis of the polarization ellipse changed from a predominantly NW‐SE direction in the local morning to a mixed NW‐SE/NE‐SW direction in the afternoon. These two statistical results are consistent with the excitation of the waves by the Kelvin‐Helmholtz instability at the magnetopause. However, frequent changes in phase are often observed in the magnetic variations, which result in polarization variations on the time scale of minutes, a situation not readily reconcilable with the Kelvin‐Helmholtz instability. The existence of the waves at very low latitudes, furthermore, places constraints on the damping rate of externally excited surface waves inside the magnetosphere. We conclude that present theories for hydromagnetic waves in the geomagnetosphere cannot readily incorporate all of these low‐latitude results.