[1] Simultaneous two-dimensional observations of airglow enhancement and radar backscatter from field-aligned irregularities (FAIs) associated with polar cap patches were conducted. The spatial structure of 630 nm airglow from polar cap patches was imaged using an all-sky airglow imager at Resolute Bay, Canada, while backscatter echoes from decameter-scale FAIs were observed using the newly constructed HF Polar Dual Auroral Radar Network (PolarDARN) radar at Rankin Inlet, Canada. Both the airglow enhancement and the radar backscatter appeared within a structured region with the spatial extent of about 500-1000 km. The decameter-scale FAIs were found to extend over the entire region of airglow enhancement associated with polar cap patches, indicating that the polar patch plasma became almost fully structured soon after initiation (within approximately 20-25 min). These findings imply that some rapid structuring process of the entire patch area is involved in addition to the primary gradient-drift instabilities.

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Abstract. A long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (K p 7-and IMF B z < 0). The ionosondes measured electron densities of up to 9´10 11 m A3 in the patch center, an increase above the density minimum between patches by a factor of $4.5. Bands of F-region irregularities generated at the equatorward edge of the patches were tracked by HF radars. The backscatter bands were swept northward and eastward across the polar cap in a fan-like formation as the afternoon convection cell expanded due to the IMF B y > 0. Near the north magnetic pole, an all-sky imager observed the 630-nm emission patches of a distinctly band-like shape drifting northeastward to eastward. The 630-nm emission patches were associated with the density patches and backscatter bands. The patches originated in, or near, the cusp footprint where they were formed by convection bursts (¯ow channel events, FCEs) structuring the solar EUV-produced photoionization and the particle-produced auroral/cusp ionization by segmenting it into elongated patches. Just equatorward of the cusp footprint Pc5 ®eld line resonances (FLRs) were observed by magnetometers, riometers and VHF/HF radars. The AC electric ®eld associated with the FLRs resulted in a poleward-progressing zonal¯ow pattern and backscatter bands. The VHF radar Doppler spectra indicated the presence of steep electron density gradients which, through the gradient drift instability, can lead to the generation of the ionospheric irregularities found in patches. The FLRs and FCEs were associated with poleward-progressing DPY currents (Hall currents modulated by the IMF B y ) and riometer absorption enhancements. The temporal and spatial characteristics of the VHF backscatter and associated riometer absorptions closely resembled those of poleward moving auroral forms (PMAFs). In the solar wind, IMP 8 observed large amplitude Alfve n waves that were correlated with Pc5 pulsations observed by the ground magnetometers, riometers and radars. It is concluded that the FLRs and FCEs that produced patches were driven by solar wind Alfve n waves coupling to the dayside magnetosphere. During a period of southward IMF the dawn-dusk electric ®eld associated with the Alfve n waves modulated the subsolar magnetic reconnection into pulses that resulted in convection¯ow bursts mapping to the ionospheric footprint of the cusp.

Abstract. The Cascade Demonstrator Small-Sat and Ionospheric Polar Explorer (CASSIOPE) satellite is scheduled to be launched in 2010. On board this satellite will be a suite of eight scientific instruments comprising the enhanced Polar Outflow Probe (ePOP). One instrument is the Radio Receiver Instrument (RRI) which will be used to receive HF transmissions from various ground transmitters such as the Super Dual Auroral Radar Network (SuperDARN) array. Magnetoionic polarization and propagation theory have been used to model the relative power that SuperDARN delivers to the Ordinary (O) and Extraordinary (X) modes of propagation. These calculations have been performed for various frequencies in the SuperDARN transmitting band and for all five Canadian based SuperDARN radars. The geometry of the radars with respect to the background magnetic field results in the X-mode dominating the transmitted signal when the modelled wave propagates northward and is nearly perpendicular to the magnetic field lines. Other propagation directions (i.e., above or southwards of the radar) results in propagation which is anti-parallel to the magnetic field lines and an equal splitting of transmitted power between the O-and X-modes occurs. The modelling analysis shows that for either high transmitting frequencies or low ionospheric electron densities, the range of latitudes that signal will be received is quite large (up to ∼90 • of latitude). Also for these conditions, the range of elevations where the X-mode signal strongly dominates the O-mode signal will be apparent in the received signal. Conversely, for lower transmitting frequencies or higher ionospheric electron densities, the latitudinal range that signal will be received over is smaller. Here the X-mode-only band is not apparent in the received signal as both modes will be received with roughly equal power. These relative mode power calculations can be used to characterize Correspondence to: R. G. Gillies (rob.gillies@usask.ca) the average electron density content in the ionosphere or provide a measure of relative absorption in the D-and E-regions when the satellite passes through the field-of-view of a SuperDARN radar.

[1] A study of the dynamics of ionospheric plasma convection in the postmidnight sector during the substorm expansion phase (EP) is presented. We have found that after the substorm onset, a postmidnight anticlockwise convection vortex (PoACV) usually emerges at latitudes higher than the auroral brightening region, and an east-to-west flow reversal wrapping around the intensified auroras extends into the postmidnight sector. The substorm current system inferred from the relative positions of the PoACV and the auroral brightening region is in general northeast-southwest aligned, implying a mixture of a meridional current system (MCS) and a zonal system associated with the substorm current wedge (SCW). The time delay between the formation of the PoACV and the onset depends upon the relative azimuthal location of the PoACV and the auroral brightening region. The observed postmidnight convection pattern, namely, a PoACV at higher latitudes, and an east-to-west flow reversal region at lower latitudes, can be explained by a combination of the nightside reconnection and the ''field line slippage'' process associated with dipolarization. Finally, we suggest that strong negative IMF By is the most unfavorable condition for the evolution of the PoACV.Citation: Liang, J., G. J. Sofko, and H. U. Frey (2006), Postmidnight convection dynamics during substorm expansion phase,