Lower ionospheric variations under intense SAID: simulations and implication to the STEVE and Picket Fence phenomena

Abstract:

STEVE and Picket Fence are nightsky optical phenomena that are relatively new to the science community. While significant advancements have been achieved in recent years toward our understanding of the STEVE and Picket Fence, their main production mechanisms remain to be explored. STEVE is found to be co-located with the fast subauroral ion drift (SAID) channel, while the Picket Fence, if co-existing, is also likely to be in close vicinity of the SAID channel but in a lower altitude range (~100-120 km). The local ionospheric/thermospheric variations under a narrow SAID channel are crucial to the generation of STEVE and Picket Fence. While SAID has been known and studied for decades, most of the existing measurements and research focus were in the upper/topside ionosphere. Observations and knowledge of the ionospheric variations in the E-and lower F-region under SAID are scarce to date. In this study, based upon realistic SAID parameters associated with STEVE in reported in-situ measurements, we develop a model to simulate and investigate the time-dependent and self-consistent variations of ionospheric electron/ion temperature and plasma density, as well as certain neutral constituents that might be of particular importance to the STEVE/Picket Fence, under intense SAID. As compared to some existing models we have taken into account two effects that are particularly important in the lower ionosphere: the anomalous heating led by strong SAID electric field, and the demagnetized ion drift across the SAID channel. Besides some known features of SAID such as intense Joule heating of ions, strong electron heating and density depletion in the upper F region, our simulation results bring new insights into the temporal/spatial variations of the temperature, density, and conductivity in the E- and lower F-region ionosphere under SAID. We discuss some potential implications of our results to the generation mechanisms of STEVE and Picket Fence.