Using data from the polar orbiting satellite 1963 38C, we have studied the behavior of day‐side intensities of trapped electrons in the energy ranges Ee ≥ 280 kev and ≥1.2 Mev during the period October 1 through November 1, 1963. During this time the satellite orbital plane was within 30° of the earth‐sun line. The data show (a) at L = 2 no apparent correlation of charged particle intensities with magnetic activity, (b) at L = 2.5 and 3 the trapped electrons are effected only by intense magnetic activity, (c) in the range 3.5 ≲ L ≲ 6 the trapped intensities follow the general trend of the magnetic activity including the 27‐day recurring increase in the level of magnetic activity, and (d) above L ∼ 6 the trapped electrons become much more sensitive to the detailed fluctuations in the magnetic activity indices. Quiet time data show a steady decay in trapped intensities for L ≥ 3. Time delays in the particle response to magnetic variations are found to increase with both increasing energy and L value. A rough correlation of the energy spectrum with magnetic activity is obtained.

Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identi®ed as possible candidates for polar-cap patches drifting anti-Sunward with the plasma¯ow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.

Abstract. Observations are presented of the polar ionosphere under steady, northward IMF. The measurements, made by six complementary experimental techniques, including radio tomography, all-sky and meridian scanning photometer optical imaging, incoherent and coherent scatter radars and satellite particle detection, reveal plasma parameters consistent with ionospheric signatures of lobe reconnection. The optical green-line footprint of the reconnection site is seen to lie in the sunward plasma convection of the lobe cells. Downstream in the region of softer precipitation the reverse energy dispersion of the incoming ions can be identi®ed. A steep latitudinal density gradient at the equatorward edge of the precipitation identi®es the general location of an adiaroic boundary, separating the open ®eld lines of polar lobe cells from the closed ®eld of viscous-driven cells. Enhancements in plasma density to the south of the gradient are interpreted as ionisation being recon®gured as it is thrust against the boundary by the antisunward¯ow of the viscous cells near noon. Each of the instruments individually provides valuable information on certain aspects of the ionosphere, but the paper demonstrates that taken together the dierent experiments complement each other to give a consistent and comprehensive picture of the dayside polar ionosphere.

Abstract. Results are presented from a multi-instrument investigation of the signatures of equatorial reconnection in the summer, sunlit ionosphere. Well-established ion dispersion signatures measured during three DMSP satellite passes were used to identify footprints in ionospheric observations made by radio tomography, and both the EISCAT ESR and mainland radars. Under the prevalent conditions of southward IMF with the Bz component increasing in magnitude, the reconnection footprint was seen to move equatorward through the ESR ®eld-of-view. The most striking signature was in the electron temperatures of the F2 region measured by the EISCAT mainland radar that revealed signi®cantly enhanced temperatures with a steep equatorward edge, in general agreement with the leading edge of the ion dispersion. It is suggested that this sharp transition in the electron temperature may be an indicator of the boundary, mapping from the reconnection site, between closed geomagnetic ®eld lines and those opened along which magnetosheath ions precipitate.

Abstract. The paper focuses on ionospheric signatures of lobe reconnection near magnetic noon under steady northward IMF. Enhanced Type 2 aurora observed by a meridian scanning photometer and reverse ion energy dispersion measured during a DMSP satellite pass provide evidence for the reconnection. Tomographic imaging of the spatial plasma distribution reveals key footprints of the processes, including the location of the adiaroic boundary separating the lobe cells from the closed LLBL precipitation, the dispersion of precipitating soft ions along sunward convecting field lines, and the possible presence of a Birkeland current sheet at the adiaroic boundary.

Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identi®ed as possible candidates for polar-cap patches drifting anti-Sunward with the plasma¯ow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.

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Abstract.Observations by the EISCAT Svalbard radar are presented that show the response of the spatial structure of the ionosphere in the dayside cusp region to a rotational trend in the IMF clock angle. Over a period of one hour, the clock angle increased from about 45 • to some 150 • , moving the likely location of the magnetopause reconnection site from the high-latitude lobe to near the equatorial plane. Increased topside electron temperatures measured by the ESR identified footprints of the reconnection process. Temporal changes in the spatial distribution of the temperature reflected the change from lobe to equatorial reconnection. Discrete spatial enhancements in ion temperature were found resulting from ion-neutral frictional heating in the fast flows where it was likely that field lines were being convected from the reconnection locations. The corresponding electron density structuring is interpreted in terms of the particle precipitation, field-aligned currents and convection flows driven by the IMF.