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Observations from August 2 and 3, 1991, of poleward progressing, dayside convection disturbances accompanied by geomagnetic perturbations and ionospheric radio wave absorption have been analyzed and compared to variations in the solar wind parameters as observed from the IMP 8 satellite. The convection disturbances appear to start at dayside cusp latitudes from where they progress antisunward to high latitudes. The reported observations have enabled calculations of the progression directions and velocities and precise estimates of the delays between solar wind variations as measured by the IMP 8 satellite and ionospheric convection changes as observed from an array of polar magnetic observatories. The progressing ionospheric disturbance events occur during intervals of southward interplanetary magnetic fields (negative interplanetary magnetic field (IMF) B z component); they are found to be closely related to variations of the east-west component B r of the IMF. The close coupling between the solar wind and the polar ionosphere(s) is explained in an open magnetospheric model in which the geomagnetic field extending from a localized region of the dayside polar cap merges with the southward interplanetary field. Variations in the IMF B r component are reproduced in corresponding modulations of the east-west component of the plasma flow at the ionospheric foot points of the connecting "open" field lines. The perturbations of the plasma flow persist while the open field lines are convected with the ionospheric plasma across part of the dayside polar cap. The observed geomagnetic perturbations result from the combined effects of field-aligned currents and horizontal ionospheric currents, notably the convection-related Hall currents. The associated radio wave absorption events are explained as the result of E region electron heating by the horizontal electric fields associated with the convection enhancements.

Sudden changes in the solar wind dynamic pressure have been linked, both theoretically and observationally, to the formation of a number of transient ionospheric phenomena. Still, the precise role that these pressure changes play in the formation of these phenomena remains uncertain. By using a combination of ground‐based magnetic measurements from arrays of magnetometers located in Greenland and IMP 8 satellite measurements of the solar wind velocity and density, we have been able to better study the effect that pressure changes have on the high‐latitude ionosphere. Our study is based on approximately 2500 hours of solar wind plasma data collected during 1991 and 1992 by the IMP 8 satellite and focuses on step changes of |Δp | > 2 nPa occurring on a timescale of Δt < 15 min. We have found that the ground response does not consistently conform to existing theoretical models of field‐aligned currents generated by changes in dynamic pressure. We also do not find any explicit dependence on interplanetary magnetic field orientation. These results lead us to believe that the nature of the ground response is due to a more complicated combination of external controls.

We report here a collection of complementary measurements near local magnetic noon of a unique ionospheric convection variation observed by the Sondrestrom radar which is related to a nearly periodic variation (• 25 -30 min period) in the interplanetary magnetic field By component. We observe also a poleward phase propagation of magnetic pulsations over a region limited in longitude and latitude near the dayside polar cusp. A series of poleward propagating radio absorption enhancements are observed in the Greenland and South Pole imaging riometer data. The pulsations and absorption enhancements are associated with a latitudinally narrow and longitudinally limited intensification of the westward convection and associated eastward Hall current, which propagates poleward over the magnetometers and radar field of view. For the cases presented the interplanetary Bz is strongly negative, while the ionospheric variations are associated with the low-frequency component of variations in the interplanetary By component. In contrast to the previously discovered traveling convection vortices, these features exhibit a poleward phase motion rather than one along lines of invariant latitude. The propagation velocity is slower (• 0.5-1.0 km/s) and the structures cover 2 to 3 hours of local time. We interpret the observations as a poleward propagation of the DPY current system intensification associated with enhancements in the IMF By component. Our observations indicate that the DPY field-aligned current system is propagating poleward and may be moving independent of the convection motion of the plasma and associated field lines. Introduction The distribution of dayside ionospheric currents is known to be strongly controlled by the orientation of the interplanetary magnetic field. Friis-Christensen and Wilhjelm [1975] investigated the relationship between geomagnetic disturbances measured at high dayside latitudes and the interplanetery magnetic field (IMF). The DP Y mode of the disturbance field related to the IMF By component was discovered m•d subsequently attributed to an east-west ionospheric Hall current now called the DPY current. More recent investigations using ground magnetometers and high-latitude ionospheric radars show that the dayside high-latitude currents and electric field distributions depend strongly

Abstract.We discuss a set of coordinated observations from the arrays of Greenland ground magnetometers, Sondrestrorn incoherent scatter radar, and the DMSP, GOES 7, and IMP 8 satellites during 1000-1400 UT on August 4, 1991. The work presented here follows work presented by Clauer and Ridley [1995]. In the previous work we show that this particular interval is characterized by a large positive interplanetary magnetic field (IMF) By and near-zero IMF Bz components. Associated with these conditions is a very strong ionospheric convection shear reversal boundary in the dayside noon and prenoon sector in the northern hemisphere. The convection reversal boundary is observed to be very dynamic, showing wave-like displacements of several degrees in invariant latitude with a tailward phase propagation. These variations are associated with magnetic pulsations with a period of about 34 min. We have suggested that these waves are produced by a Kelvin-Helrnholtz instability at the shear convection reversal boundary. We present here a more detailed analysis of the magnetic variations from the Greenland arrays of magnetometers. Our new findings show that equatorward of the convection reversal boundary, there is power in the pulsation spectra in bands with periods of about 34, 17, 12, and 8 min. Examination of the northward component of the pulsations along a rneridional chain of stations ranging from 76.23 ø to 66.86 ø invariant latitude shows high coherence between stations and a change in relative phase of about 160 ø over the observed latitude range for the 8-rnin. pulsations. These observations are consistent with the expected signature of a field line resonance. We suggest that the source of the resonance is the disturbance generated at the shear convection reversal boundary which then produces resonances on nearby, equatorward closed field lines. In this case we suggest that the source is the Kelvin-Helrnholtz wave established at the east-west convection shear which develops near local noon and prenoon regions during large IMF By positive conditions. This is possibly the first observation of the field line resonance associated with such a source.