The formation of polar cap density enhancements, such as tongues‐of‐ionization (TOIs), are often attributed to enhanced dayside reconnection and convection due to solar wind changes. However, ionospheric poleward moving density enhancements can also form in the absence of changes in the solar wind. This study examines how TOI and patch events that are not triggered by solar wind changes relate to magnetospheric processes, specifically substorms. Based on total electron content and Super Dual Auroral Radar Network (SuperDARN) observations, we find substorms that occur at the same time as TOIs are associated with sudden enhancements in dayside poleward flows during the substorm expansion phase. Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) observations also show enhanced field‐aligned currents (FACs) that extend into the dayside ionosphere during this period. We suggest that the global enhancement of FACs and convection during these substorms are the drivers of these TOIs by enhancing dayside convection and transporting high‐density lower‐latitude plasma into the polar cap. However, we also find that not all substorms are coincident with polar cap density enhancements. A superposed epoch study showed that the AL index for TOIs during substorms is not particularly stronger than substorms without TOIs, but epoch studies of AMPERE observations do show events with TOIs to have a higher total FAC on both the dayside and nightside. Our results show the importance of TOI formation during substorms when solar wind drivers are absent, and the importance of considering substorms in the global current system. This work also shows the need to incorporate substorms into models of high‐latitude global convection and currents.
This content will become publicly available on December 14, 2024
Simultaneous observations from Defense Meteorological Satellite Program, Swarm, Resolute Bay all‐sky imagers, GPS Total Electron Content and Super Dual Auroral Radar Network, are used to investigate the evolution and key characteristics of the Tongue of Ionization (TOI) being restructured into a polar cap patch. Six satellites crossed the TOI of patch as it moved from the dayside to the nightside. It was initially hot, then a mix of both cold and hot, and finally it became a cold patch. This suggests that cold patch is not only a result of solar extreme ultraviolet radiation, but may also develop when a hot patch cools down. Soft‐electron precipitation and flow shears both contribute to the TOI restructuring and the appearance of polar cap patch. The plasma density of patch at ∼500 km was at least 4 times higher than at ∼800 km. The plasma density enhancement gradually decreased as the patch evolved due to decreased production and transport of cold nightside low‐density plasma. Moreover, the duskward motion of the patch was influenced by changes in the ionospheric convection pattern.
more » « less- NSF-PAR ID:
- 10480835
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 128
- Issue:
- 12
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Dayside solar‐produced concentrated
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