The storm‐time ionospheric‐thermospheric (IT) state is of great interest, since the IT dynamics change dramatically as energy is input and dissipated in the upper atmosphere. Lagrangian coherent structures (LCSs), which are objective ridges in time‐evolving flows that describe the tendency of neighboring fluid elements to separate, provides a unique opportunity to infer the dynamics in the IT system. In this work, we model IT flows with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model and identify the LCSs. We compare the LCSs in the neutral winds and plasma drifts during quiet times versus during active times. We find that LCSs are largely aligned in the modeled IT flows, with a dawn‐dusk asymmetry in their latitudinal position. During a geomagnetic storm, the thermospheric LCSs (T‐LCSs) and ionospheric LCSs (I‐LCSs) shift equatorward, align more closely with each other, and maintain a dawn‐dusk asymmetry. The collocation of T‐LCSs and I‐LCSs and their analogous response to the geomagnetic storm provide evidence of energy input into the thermosphere and ionosphere simultaneously, and the ion drag is the dominant effect causing LCS alignment during a geomagnetic storm.
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- 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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