Coordinated observations of dayside polar cap airglow patches by all-sky imagers and DMSP

Abstract:

Recent imager and radar observations in the nightside polar cap have shown evidence of localized flow channels propagating anti-sunward, and polar cap patches are often associated with such flow channels. It is crucial to understand how these polar cap flow channels and patches are created and propagate deep into the polar cap. In our study, we use all-sky imagers of the AGO network in Antarctica for dayside patch observations and DMSP for measuring density and velocity associated with the patches. We have identified 39 conjunction events in during the southern winter seasons of 2007-2011, the conjunctions being primarily in the pre-noon sector due to the MLT of the satellite orbit. We find that longitudinally narrow flow enhancements directed anti-sunward are well collocated with patches for all events. The flows over the patches are typically ~1000 m/s and are substantially larger than the weak large-scale background flows, and the widths of the flow enhancement are similar to the patch widths (~400 km). The flow channel speeds average 1070 m/sec over the observed patches, and the average width is 302 km. We also investigated the IMF Bz, IMF clock angle and oval-patch distance dependences of properties of the airglow patches and related fast flows. We found that the airglow patches propagating deeper into the polar cap have with higher density. The patches with fast peaks flow speeds >~2000 m/s are predominantly seen near the auroral oval, and those patches tend to propagate azimuthally away from noon without substantial poleward propagation. The peak flow speeds of patches propagating deep into the polar cap are smaller, but still reach ~1000 m/s for our cases which extend to about 6° away from the auroral oval. Fast flows of >~2000 m/s are predominantly seen during large IMF –By and small |Bz|, and the flow speed decreases with increasing –Bz. The –By preference is consistent with the duskside convection cell extending toward dawn and giving a higher possibility of a flow channels being seen on the dawnside. The presence of fast, anti-sunward flow channels associated with the polar cap patches suggests that the flow channels form in the dayside polar region, and can serve as the source of flow channels measured in the nightside polar cap.