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Abstract Two quasi‐orthogonal nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) were observed by conjugate midlatitude all‐sky imagers in Sutherland (32.4S, 20.8E; magnetic latitude: −40.9) and Asiago (45.87N, 11.53E; magnetic latitude: ) on 4 October 2018. These MSTIDs had fronts elongated quasi‐orthogonally to one another as observed from each location. The first MSTID was aligned northeast‐southwest (NE‐SW) in the Southern Hemisphere (SH) and northwest‐southeast (NW‐SE) in the Northern Hemisphere (NH) and propagated equator‐westwards. These properties are typically attributed to MSTIDs generated through the coupled Perkins and sporadic E instabilities. This is supported by observed conditions in both hemispheres indicating the presence of sporadic E layers and reasonable Perkins instability growth rates. The second MSTID was aligned NW‐SE (SH) and NE‐SW (NH) and propagated equator‐eastwards and represents the first optical observations of conjugate equator‐eastward propagating MSTIDs. A possible linkage to gravity wave‐induced polarization electric fields in the NH (and mapped to the SH) is presented, as significant gravity wave activity was observed in OH and OI greenline observations by the Asiago imager. Their equator‐eastward propagation direction was favored by background winds at the hemisphere of origin, as determined from global model observations.
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Simulation of Nighttime Medium‐Scale Traveling Ionospheric Disturbances in the Midlatitude Ionosphere During Stormtime
Abstract The generation of medium‐scale traveling ionospheric disturbances (MSTIDs) in the mid‐latitude F region ionosphere, particularly in the presence of sporadic E (Es) layers or geomagnetically conjugate features, has been the focus of extensive investigation using both observational and numerical modeling approaches. Recent observations have revealed the occurrence of nighttime MSTIDs over the continental US during storm conditions even without invoking the Es instability. While this phenomenon is considered to be electrified and likely associated with the Perkins instability, the influences of storm‐enhanced density (SED), electric fields, and winds on the excitation of nighttime MSTIDs remain a complicated issue and require further quantitative analysis. In this study, we develop a two‐dimensional numerical model of the nighttime ionospheric electrodynamics at midlatitudes using the ionospheric ion continuity equation and the electric field Poisson equation to investigate the characteristics of MSTIDs in the SED base region during storm conditions. We demonstrate that the magnetic inclination effect can explain the lower latitude preference of the MSTIDs during magnetic storms, while the development of MSTIDs is primarily influenced by intense storm electric fields under the background ionospheric condition of large density gradients associated with SED. However, the impact of neutral winds on the MSTIDs growth varies, depending on their specific direction determined by the strongly dynamic spatiotemporal variation of the thermosphere and ionosphere during storms. Therefore, the MSTIDs stormtime scenario results from a combination of multiple important factors.
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- PAR ID:
- 10571673
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 129
- Issue:
- 6
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2023ja032051
