Abstract
We use simultaneous auroral imaging, radar flows, and total electron content (TEC) measurements over Alaska to examine whether there is a direct connection of large-scale traveling ionospheric disturbances (LSTIDs) to auroral streamers and associated flow channels having significant ground magnetic decreases. Observations from seven nights with clearly observable flow channels and/or auroral streamers were selected for analysis. Auroral observations allow identification of streamers, and TEC observations detect ionization enhancements associated with streamer electron precipitation. Radar observations allow direct detection of flow channels. The TEC observations show direct connection of streamers to TIDs propagating equatorward from the equatorward boundary of the auroral oval. The TIDs are also distinguished from the streamers to which they connect by their wave-like TEC fluctuations moving more slowly equatorward than the TEC enhancements from streamer electron precipitation. TIDs previously observed propagating equatorward from the auroral oval have been identified as LSTIDs. Thus, the TIDs here are likely LSTIDs, but we lack sufficient TEC coverage necessary to demonstrate that they are indeed large scale. Furthermore, each of our events shows TID’s connection to groups of a few streamers and flow channels over a period in the order of 15 min and a longitude range of ∼15–20°, and not to single streamers. (Groups of streamers are common during substorms. However, it is not currently known if streamers and associated flow channels typically occur in such groups.) We also find evidence that a flow channel must lead to a sufficiently large ionospheric current for it to lead to a detectable LSTID, with a few tens of nT ground magnetic field decreases not being sufficient.
Highlights
Heating and momentum transfer to the upper atmosphere within the auroral oval can lead to neutral atmospheric gravity waves
We considered seven nights of observations from our previous studies that had good auroral viewing and clear observations of flow channels and/or streamers. 12 separate relatively ideal events were analyzed, and these events have allowed us to minimize ambiguities in looking for the direct connection of streamers with TIDs
Note that we have recently found interesting azimuthal diversion and expansion of flow channels as they approach the equatorward portion of the auroral oval/near-Earth plasma sheet (Wang et al, 2018; Lyons et al, 2021c) that has not yet been included in simulations to determine its effects on TID formation
Summary
Heating and momentum transfer to the upper atmosphere within the auroral oval can lead to neutral atmospheric gravity waves. The above suggestion would imply that the flows, electric fields, and electron precipitation associated with mesoscale flow channels drive the heating and momentum transfer that gives rise to the neutral atmospheric gravity waves that appear as LSTIDs. In the study by Lyons et al (2019), we found indications that a disturbance should have sufficiently large ground magnetic perturbation (ΔB) in order to lead to a detectable LSTID. We do not have the continentwide TEC coverage necessary to demonstrate that they are large scale
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