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- Title
A Time‐Dependent Two‐Dimensional Model Simulation of Lower Ionospheric Variations Under Intense SAID.
- Authors
Liang, Jun; St‐Maurice, J. P.; Donovan, E.
- Abstract
The subauroral ion drift (SAID) denotes a latitudinally narrow channel of fast westward ion drift in the subauroral region, often observed during geomagnetically disturbed intervals. The recently recognized subauroral optical phenomena, the Strong Thermal Emission Velocity Enhancement (STEVE) and the Picket Fence, are both related to intense SAIDs. In this study, we present a 2D time‐dependent model simulation of the self‐consistent variations of the electron/ion temperature, density, and FAC, under strong SAID, with more focus in the lower ionosphere. The anomalous electron heating in the E‐region is evaluated using an empirical model. Our simulation reproduces many key features of SAID, such as the strong electron temperature enhancement in the upper F‐region, the intense ion frictional heating, and the plasma density depletion. Most importantly, the ion Pedersen drifts is found to play a crucial role in the density variations and FAC dynamics in the lower ionosphere. The transport effect of ion Pedersen drifts leads to strong density depletion in the lower ionosphere in a large portion of SAID. The FAC inside SAID is mainly downward with magnitude ≤ ∼1 μA/m2. At the poleward edge of SAID, the ion Pedersen drift leads to a pileup of the plasma density and an upward FAC. Our simulation results also corroborate the presence of strong gradients of plasma density, temperature, and flows, at the edge of SAID, which may be conducive to certain plasma instabilities. Our model provides a useful tool for the future exploration of the generation mechanisms of STEVE and Picket Fence. Plain Language Summary: The recently recognized subauroral optical phenomena, the Strong Thermal Emission Velocity Enhancement (STEVE) and the Picket Fence, are inherently related to a special activity termed "subauroral ion drift (SAID)", namely a rapid (several km/s) westward drift of plasma in the Earth's ionosphere. Existing observations and models related to SAID are limited to the upper/topside ionosphere that is not where STEVE and Picket Fence emissions actually come from. In this study, we present a model simulation of the variations of the ionospheric state under strong SAID. In particular, we mainly focus on the lower‐altitude (<200 km) region where ions and electrons tend to move differently. The difference between the ion and electron motions leads to a redistribution of plasma densities and produce electric currents in the lower ionosphere across the SAID channel: density depletion and downward currents exist in the equatorward and center portion of SAID, while density pileup and upward currents exist near the poleward edge of SAID. A strong latitudinal gradient of plasma temperature, density, and flows, is formed at the edge of SAID. The ionospheric variations and structures across the SAID channel achieved from this study would help the exploration of the underlying mechanisms of STEVE and Picket Fence. Key Points: We present a 2D time‐dependent model simulation of the self‐consistent ionospheric variations of the Te, Ti, Ne, and FAC, under strong SAIDThe ion Pedersen drift effect leads to strong depletion of density and conductance in the lower ionosphere in a large portion of SAIDWe corroborate the presence of strong gradients of plasma density, temperature, and flows, in the lower ionosphere at the edge of SAID
- Subjects
AURORA spectra; TWO-dimensional models; COMPUTER simulation; PLASMA density; IONOSPHERIC observations
- Publication
Journal of Geophysical Research. Space Physics, 2021, Vol 126, Issue 12, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2021JA029756