The occurrence of St. Patrick's Day (17 March) geomagnetic storms during two different years (2013 and 2015) with similar solar flux levels but varying storm intensity provided an opportunity to compare and contrast the responses of the ionosphere‐thermosphere (IT) system to different levels of geomagnetic activity. The evolution of positive ionospheric storms at the southern polar stations Bharati (76.6°S MLAT) and Davis (76.2°S MLAT) and its causative connection to the solar wind driving mechanisms during these storms has been investigated in this paper. During the main phase of both the storms, significant enhancements in TEC and phase scintillation were observed in the magnetic noon/ midnight period at Bharati and Davis. The TEC in the midnight sector on 17 March 2015 was significantly higher compared to that on 17 March 2013, in line with the storm intensity. The TEC enhancements during both the storm events are associated with the formation of the storm‐enhanced densities (SEDs)/tongue of ionization (TOI). The strong and sustained magnetopause erosion led to the prevalence of stronger storm time electric fields (prompt penetration electric field (PPEF)/subauroral polarization streams (SAPS)) for long duration on 17 March 2015. This combined with the action of neutral winds at midlatitudes favored the formation of higher plasma densities in the regions of SED formation on this day. The same was weaker during the 17 March 2013 storm due to the fast fluctuating nature of interplanetary magnetic field (IMF)
Meso‐scale plasma convection and particle precipitation could be significant momentum and energy sources for the ionosphere‐thermosphere (I‐T) system. Following our previous work on the I‐T response to a typical midnight flow burst, flow bursts with different characteristics (lifetime, size, and speed) have been examined systematically with Global Ionosphere‐Thermosphere Model (GITM) simulations in this study. Differences between simulations with and without additional flow bursts are used to illustrate the impact of flow bursts on the I‐T system. The neutral density perturbation due to a flow burst increases with the lifetime, size, and flow speed of the flow burst. It was found that the neutral density perturbation is most sensitive to the size of a flow burst, increasing from ∼0.3% to ∼1.3% when the size changes from 80 to 200 km. A westward‐eastward asymmetry has been identified in neutral density, wind, and temperature perturbations, which may be due to the changing of the forcing location in geographic coordinates and the asymmetrical background state of the I‐T system. In addition to midnight flow bursts, simulations with flow bursts centered at noon, dawn, and dusk have also been carried out. A flow burst centered at noon (12.0 Local Time [LT], 73°N) produces the weakest perturbation, and a flow burst centered at dusk (18.0 LT, 71°N) produces the strongest. Single‐cell and two‐cell flow bursts induce very similar neutral density perturbation patterns.
more » « less- NSF-PAR ID:
- 10374977
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 126
- Issue:
- 10
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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