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Ionospheric plasma density structures in the dayside F‐region of the polar cap are commonly occurring events, but adequate measurements of their formation and evolution have been sparse. With the advent of the advanced modular incoherent scatter radar RISR‐N (Resolute Bay Incoherent Scatter Radar) it is now possible for the first time to study the temporal evolution of the plasma properties in the polar cap region in three dimensions, with a spatial resolution of tens of kilometers, from which the plasma rest frame can be experimentally established. We demonstrate the strength of the diagnostic with observations from an event of enhanced plasma density observed over Resolute Bay in December 2009. A colocated all‐sky imager showed faint 630.0 and 557.7 nm emission corresponding to the plasma enhancements, and the structures could be traced back to a formation region in the open/closed field line boundary. This new plasma imaging technique will provide important information on the mechanisms controlling the structuring in the high latitude ionosphere.

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[1] Measurements obtained with the electronically steerable Poker Flat Incoherent Scatter Radar (PFISR) and collocated all-sky camera were used to construct composite images of ionospheric convective flows and auroral forms during a substorm cycle (onset 26 March 2008, 1146. PFISR was configured to sample an array of 5 × 5 regularly spaced beams on a pulse-by-pulse basis, from which velocity vectors were computed via statistical inversion of groups of beams. Flow fields were resolved at 30 km spatial resolution at 2 min temporal resolution over a 100 × 100 km field and then geographically registered with all-sky imagery recorded at 20 s cadence. An analysis of the composite images has revealed interesting contrasts between growth-, expansion-, and recoveryphase auroras, for example, (1) anticorrelation of ion velocity (electric field) and luminosity (plasma density, hence, conductance) in both space and time during growth phase and expansion phase; (2) identical flow (magnitude and direction) inside and outside the aurora during recovery phase; (3) a large tangential flow component along auroral boundaries during both growth and recovery phase (consistent with electric field directed into the aurora), irrespective of the orientation of the arc boundary; and (4) large relative drift (∼2 km/s) between auroral forms and convective flow during recovery phase. These features are interpreted in the context of previous ground-based and space-borne observations. Future PFISR experiments are expected to enable flow field construction at 30 s cadence, which will resolve Alfvén transit time dynamics to putative substorm initiation regions and significantly clarify the observations presented herein.

[1] We develop a technique for using monostatic, electronically steerable incoherent scatter radar (ISR) to generate 2-D estimates of F region flow fields. Tikhonov regularization is used to achieve robustness in the presence of spatial variation. The regularization functional imposes partial incompressibility on the medium and is therefore physically justified. Although the estimator has difficulty resolving sharp discontinuities, it performs well in regions of uniform flow. In order to characterize the effect of the regularization parameter, we test the performance of the operator in three simulated scenarios. We then analyze data from an experiment on the Poker Flat ISR. The experimental results are validated against coregistered all-sky optical data and are found to be mostly consistent with these independent measurements. Namely, the radar-derived estimates show a reduction of ion flow wherever the optical data indicates an auroral enhancement. The estimated flow is directed parallel to an arc boundary, consistent with an electric field directed toward the arc.