Abstract
AbstractThis 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.
Highlights
Traveling ionospheric disturbances (TIDs) are a ubiquitous and permanent feature of upper atmospheric variability and impose a primary challenge for accurate specification and prediction of the ionosphere and Space Weather10.1029/2019SW002325 thermosphere weather
We report subauroral Medium-scale TIDs (MSTIDs) that occurred concurrently with Large-scale TIDs (LSTIDs) and were correlated to dynamic features specific to subauroral storm time response, and in particular to the existence of a fast zonal flow channel known as the subauroral polarization stream (SAPS; Foster & Burke, 2002)
This study has focused on a few unusual disturbance time TID features observed in Global Navigation Satellite System (GNSS) total electron content (TEC) during the 7–8 September 2017 geospace storms
Summary
Traveling ionospheric disturbances (TIDs) are a ubiquitous and permanent feature of upper atmospheric variability and impose a primary challenge for accurate specification and prediction of the ionosphere and. Medium-scale TIDs (MSTIDs) form another disturbance wave class that are excited through quite many processes including the high-latitude disturbances They have a typical horizontal velocity of 250–1,000 m/s, a 15- to 60-min period, a horizontal wavelength of several hundred kilometers. We report subauroral MSTIDs that occurred concurrently with LSTIDs and were correlated to dynamic features specific to subauroral storm time response, and in particular to the existence of a fast zonal flow channel known as the subauroral polarization stream (SAPS; Foster & Burke, 2002). We demonstrate an event characterized by predominant trans-polar propagation from the dayside into the nightside, opposite to the expected propagation direction for a disturbance source located in the nightside aurora These new findings raise important questions regarding storm time TID/AGW source and excitation processes at high latitudes. Our results emphasize a community need in TID propagation studies to clarify and quantify the potential conditioning influence of, and interplay with, background antisunward plasma convection conditions across the polar cap
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