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Continuous ground-based observations of ionospheric and magnetospheric regions are critical to the Geospace Environment Modeling (GEM) program. It is therefore important to establish clear intercalibrations between different ground-based instruments and satellites in order to clearly place the ground-based observations in context with the corresponding in situ satellite measurements. HF-radars operating at high latitudes are capable of observing very large spatial regions of the ionosphere on a nearly continuous basis. In this paper we report on an intercalibration study made using the Polar Anglo-American Conjugate Radar Experiment radars located at Goose Bay, Labrador, and Halley Station, Antarctica, and the Defense Meteorological Satellite Program (DMSP) satellites. The DMSP satellite data are used to provide clear identifications of the ionospheric cusp and the low-latitude boundary layer (LLBL). The radar data for eight cusp events and eight LLBL events have been examined in order to determine a radar signature of these ionospheric regions. This intercalibration indicates that the cusp is always characterized by wide, complex Doppler power spectra, whereas the LLBL is usually found to have spectra dominated by a single component. The distribution of spectral widths in the cusp is of a gcnc•any "" lrds. The •Jau•ta]] torm with .... •'-,.t. .... m•u•ouuun a la•mx of •la•,tral w,uth• in the LLBL is more like an exponential distribution, with the peak of the distribution occurring at about 50 m/s. There are a few cases in the LLBL where the Doppler power spectra are strikingly similar to those observed in the cusp. Paper number 94JA01481. 0148-0227/95/94JA-01481 $05.00 ground-based observations, submitted to Journal of Geophysical Research, 1994]. In this paper we report on the results of a study using satellite data and HF-radar data to perform a calibration of the radar data and determine the signatures of the cusp and the low-latitude boundary layer (LLBL). A significant controversy related to the cusp concerns the temporal structure of the cusp [Lockwood et al.In this paper, however, we shall not directly address this question. The results of the radar/DMSP intercalibration can be (and has been) interpreted as supporting both the steady cusp model and the pulsating cusp model. A resolution of this controversy will have to await further studies. The purpose of this paper is to establish more firmly the radar cusp/LLBL intercalibration [Baker et al., 1990b] with the DMSP observations. DMSP Identification of the Cusp and LLBL The satellite data we have chosen to use for the identification of the cusp and the LLBL is provided by the particle precipitation data from the DMSP F9 satellite [Hardy et al., 1985]. The work by Newell and his co-workers (Newell and Meng, 1988; Newell and Meng, 1989; Newell et al., 1989; Newell and Meng, 1992) has provided a firm base for the identification of the cusp and LLBL from these data. An important feature of this body of work has been the use of the ion precipitation data in ad...

Polar patches are regions within the polar cap where the F-region electron concentration and airglow emission at 630 nm are enhanced above a background level. Previous observations have demonstrated that polar patches can be readily identified in Polar Anglo-American Conjugate Experiment (PACE) data. Here PACE data and those from complementary instruments are used to show that some polar patches form in the dayside cusp within a few minutes of the simultaneous occurrence of a flow channel event (short-lived plasma jets -2 km s 'l) and azimuthal flow changes in the ionospheric convection pattern. The latter are caused by variations of the y-component of the interplanetary magnetic field. The physical processes by which these phenomena cause plasma enhancements and depletions in the vicinity of the dayside cusp and cleft are discussed. Subsequently, these features are transported into the polar cap where they continue to evolve. The spatial scale of patches when formed is usually 200-1000 km in longitude and 20-3 ø wide in latitude. Their motion after formation and the velocity of the plasma within the patches are the same, indicating that they are drifting under the action of an electric field. Occasionally, patches are observed to occur simultaneously in geomagnetic conjugate regions. Since some of these observations are incompatible with the presently-accepted model for patch formation involving the expansion of the high latitude convection pattern entraining solar-produced plasma, further modeling of the effects of energetic particle precipitation in the cusp, the consequences of flow channel events on the plasma concentrations, and the time dependence of plasma convection as a result of interplanetary magnetic field By changes is strongly recommended. Such studies could be used to determine the relative importance of this new mechanism compared with the existing theory for patch formation as a function of universal time and season. 2. Patches drift antisunward across the polar cap at 300-1000 m s -l. 3. Patches are observed during periods when the interplanetary magnetic field (IMF) Bz is negative. Paper number 93JA01501, 0148-0227/94/93JA-01501 $05.00 4. Patches have been observed in summer and winter at sunspot maximum and minimum. 5. Patches are associated with intermediate-scale irregularities (1-10kin) as indicated by spread F on ionograms and considerable scintillation activity. 6. The electron temperature of a patch is low and unstructured, indicating that energetic particles do not precipitate into it when it is within the polar cap. 7. Regions of enhanced electron concentration are also seen at 800-kin altitude. 8. Patches may form simultaneously in geomagnetically conjugate regions. The HF backscatter signature of polar patches has been identified in the Polar Anglo-American Conjugate Experiment (PACE) data by comparison with a series of simultaneous riometer, photometer, and ionosonde observations from South Pole station [Rosenberg et al., 1993]. The characteristics of the polar patches as they pass...

Transient or patchy magnetic field line merging on the dayside magnetopause, giving rise to flux transfer events (FTEs), is thought to play a significant role in energizing high‐latitude ionospheric convection during periods of southward interplanetary magnetic field. Several transient velocity patterns in the cusp ionosphere have been presented as candidate FTE signatures. Instrument limitations, combined with uncertainties about the magnetopause processes causing individual velocity transients, mean that definitive observations of the ionospheric signature of FTEs have yet to be presented. This paper describes combined observations by the PACE HF backscatter radar and the DMSP F9 polar‐orbiting satellite of a transient velocity signature in the southern hemisphere ionospheric cusp. The prevailing solar wind conditions suggest that it is the result of enhanced magnetic merging at the magnetopause. The satellite particle precipitation data associated with the transient are typically cusplike in nature. The presence of spatially discrete patches of accelerated ions at the equatorward edge of the cusp is consistent with the ion acceleration that could occur with merging. The combined radar line‐of‐sight velocity data and the satellite transverse plasma drift data are consistent with a channel of enhanced convection superposed on the ambient cusp plasma flow. This channel is at least 900 km in longitudinal extent but only 100 km wide. It is zonally aligned for most of its extent, except at the western limit where it rotates sharply poleward. Weak return flow is observed outside the channel. These observations are compared with and contrasted to similar events seen by the EISCAT radar and by optical instruments.

Abstract. The Halley PACE HF radar has been operated in a new mode to provide very high time (10 s) and space (15 km) resolution measurements of the iono-spheric signatures of the cusp and the low-latitude boundary layer. The first data show that the iono-spheric signature of flux transfer events occur up to 300 km equatorward of regions showing the HF characteristics of the ionospheric cusp. Whilst larger flux transfer events are seen, on average, every 7 min, many much smaller and short-duration events have been identified. On one occasion DMSP data have been used to show that at least four flux transfer events are occurring simultaneously at the edge of the cusp over 2 h of MLT. There is strong, but not conclusive evidence, that reconnection at the magnetopause is both intermittent and patchy. These data also suggest that flux transfer events can be a significant contributor to the cross-polar cap potential.