Meso-scale Polar Cap Flows and their Impact on Polar Cap Patch Evolution

The ionosphere-thermosphere system is a highly dynamic region impacted by large- and mesoscale driving. Polar cap patches are dense regions of plasma in the F-region ionosphere at least twice as dense as surrounding plasma. On a large-scale, polar cap patch behavior is generally understood to follow the large-scale antisunward convection in a southward IMF. Although meso-scale convection is known to exist, their evolution and impact on the patches are not as well understood. Characterizing the lifetime, structure, and effect of mesoscale ionospheric flows will provide context as to how they might impact and/or drive polar cap patch propagation and evolution. Additionally, polar cap patches can disrupt GPS signals, and thus this characterization of polar cap patches will not only provide insight into the structure, dynamics, and coupling process of the ionosphere and thermosphere, but also the potential space weather impacts.

In this study, we present the evolution of polar cap patches in relation to the mesoscale ionospheric flow structures on five nights with polar cap patch airglow emissions using redline optical data from the OMTI All-Sky-Imager located at Eureka, Canada and high resolution convection maps from SuperDARN. We found that, within the large-scale ionospheric flow pattern, there exists mesoscale flow channels that are colocated with the polar cap patches. These mesoscale flow channels change on a smaller spatial and temporal scales than the large scale ionospheric flows. The polar cap patches respond to changes in the direction and strength of the mesoscale flow channels contained in the large-scale ionosphere flow patterns, often slowing down and fading soon after the mesoscale flows cease or becoming brighter and/or changing direction as other flow channels appear. These results show that polar cap flows often involve meso-scale flow channels, and that polar cap patch behavior is closely tied to mesoscale flow channels.