Subauroral and Polar Traveling Ionospheric Disturbances During the 7–9 September 2017 Storms. Issue 12 (25th December 2019)

• Record Type: Journal Article
• Authors: Zhang, Shun‐Rong; Erickson, Philip J.; Coster, Anthea J.; Rideout, William; Vierinen, Juha; Jonah, Olusegun; Goncharenko, Larisa P.
• Is Part Of: Space weather. Volume 17:Issue 12(2019)
• Page Start: 1748
• Page End: 1764
• Publication Date: 2019-12-25
• Subjects: traveling ionospheric disturbances -- subauroral dynamics -- polar cap -- ionosphere‐thermosphere coupling -- GNSS -- IS Radar; Space environment -- Periodicals; 551.509992
• DOI: 10.1029/2019SW002325
• Languages: English
• ISSNs: 1542-7390

Abstract

Abstract: This study provides new scenarios for storm time traveling ionospheric disturbance excitation and subsequent propagation at subauroral and polar latitudes. We used ground‐based total electron content observations from Global Navigation Satellite System receivers combined with wide field, subauroral ionospheric plasma parameters measured with the Millstone Hill Incoherent Scatter Radar during strong September 2017 geospace storms. Observations provide the first evidence of significant influences on traveling ionospheric disturbance (TID) propagation and excitation caused by the presence of large subauroral polarization stream flow channels. Simultaneous large‐ and medium‐scale TIDs evolved during the event in a broad subauroral and midlatitude area near dusk. Similar concurrent TIDs occurred near dawn sectors as well during a period of sustained southward Bz. Medium‐scale TIDs at subauroral and midlatitudes had wave fronts aligned northwest‐southeast near dusk, and northeast‐southwest near dawn. These wave fronts were highly correlated with the direction of storm time large zonal plasma drift enhancements at these latitudes. At high latitudes, unexpected, predominant, and persistent storm time TIDs were identified with 2000+ km zonal wave fronts and 15% total electron content perturbation amplitudes, moving in transpolar propagation pathways from the dayside into the nightside. This propagation direction in the polar region was opposite to the normal assumption that TIDs originated in the nightside auroral region. Results suggest that significant dayside sources, such as cusp regions, can be efficient in generating transpolar TIDs during geospace storm intervals. Plain Language Summary: This paper reports several new findings on the traveling ionospheric disturbances (TIDs) excited during geospace storms in 7–8 September 2017. Storm time TIDs provide pathway for momentum and energy dispersion from the solar wind‐magnetosphere system to various components of the global ionosphere and thermosphere. Storm time large‐scale TIDs (LSTIDs) have been identified by many studies as being initiated generally in the auroral zone where significant heating is injected, with subsequent propagation away from the source: equatorward into lower latitudes and poleward into high latitudes. Our study indicates that, during equatorward propagation, LSTIDs can encounter strong dynamic forcing at subauroral latitudes in the zonal direction. This westward velocity forcing is provided by a SAPS (subauroral polarization stream) channel and furthermore appears to be associated with the developing of medium‐scale TIDs (MSTIDs). Thus, this paper provides the first causal link between these TIDs and SAPS flow channels. Concurrent LSTIDs and MSTIDs existed during the September storm in not only near dusk but also dawn sectors. In the polar cap region, conventionally anticipated poleward propagation away from the auroral zone was unexpectedly weak. In contrast, an opposite sense of transpolar propagation from the dayside into the nightside (i.e., equatorward at night and poleward during the day) was observed and furthermore was persistent and large in amplitude. This unexpected propagation may imply an efficient additional storm time source region of TID excitation at high latitudes on the dayside, for example, near the cusp. This study demonstrates that modern TID studies have continued potential for fresh insights into magnetosphere‐ionosphere‐thermosphere coupling processes. Key Points: First evidence of storm time concurrent large and medium spatial scale traveling ionospheric disturbances at subauroral latitudes was reported Casual relation between medium‐scale traveling ionospheric disturbances and the subauroral polarization stream were found Unexpected persistent transpolar day‐to‐night propagation of traveling ionospheric disturbances occurred