Abstract
AbstractThis paper presents a new algorithm for detecting high‐speed flow channels in the polar cap. The algorithm was applied to Super Dual Auroral Radar Network data, specifically to data from the new Longyearbyen radar. This radar is located at 78.2°N, 16.0°E geographical coordinates looking north‐east, and is therefore at an ideal location to measure flow channels in the high‐latitude polar cap. The algorithm detected >500 events over 1 year of observations, and within this paper two case studies are considered in more detail. A flow channel on “old‐open field lines” located on the dawn flank was directly driven under quiet conditions over 13 min. This flow channel contributed to a significant fraction (60%) of the cross polar cap potential and was located on the edge of a polar cap arc. Another case study follows the development of a flow channel on newly opened field lines within the cusp. This flow channel is a spontaneously driven event forming under strong solar wind driving and is intermittently excited over the course of almost an hour. As they provide a high fraction of the cross polar cap potential, these small‐scale structures are vital for understanding the transport of magnetic flux over the polar cap.
Highlights
This paper presents a new algorithm for detecting high-speed flow channels in the polar cap
For southward interplanetary magnetic field (IMF), the high-latitude plasma convection in the ionosphere can be described on the large scale as twin-cell convection, which flows antisunward across the polar cap and returns to the dayside at auroral latitudes
This schematic view is supported by the previously discussed flows in the fan plots shown in Figure 7 as the reversal poleward of the channel is consistent with an upward current (C1) and the auroral precipitation (PCA), while R1 is colocated with the shear between antisunward flow across the polar cap and sunward return flow on closed field lines in the dawn auroral oval
Summary
For southward interplanetary magnetic field (IMF), the high-latitude plasma convection in the ionosphere can be described on the large scale as twin-cell convection, which flows antisunward across the polar cap and returns to the dayside at auroral latitudes. On a smaller scale (100–500 km), convection within the polar cap is not a uniform, laminar flow but is instead frequently driven by dynamic mesoscale phenomena These structured flow enhancements occur at many locations and are classified under different names within the literature depending on their location, speed, size, and duration. The statistics of the nightside flow channels have been studied by Gabrielse et al (2018) and they find that the flow channels are aligned with the large-scale background convection They find a postmidnight preference in the polar cap flows, which is similar to the behavior of PCAs. Previous work involving flow channels has largely been based on data from satellite passes (e.g., Sandholt & Farrugia, 2009), where the flow channel can only be sampled once per orbit and do not describe the temporal evolution of the flow channel. A future paper will study the statistics of the detected flow channels
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