We present simulation results of the vertical structure of Large Scale Traveling Ionospheric Disturbances (LSTIDs) during synthetic geomagnetic storms. These data are produced using a one-way coupled SAMI3/GITM model, where GITM (Global Ionosphere Thermosphere Model) provides thermospheric information to SAMI3 (SAMI3 is Another Model of the Ionosphere), allowing the production and propagation of LSTIDs. We show simulation results which demonstrate that the traveling atmospheric disturbances (TADs) generated in GITM propagate to the topside ionosphere in SAMI3 as LSTIDs. The speed and wavelength (900 m/s and 10º-20º latitude) are consistent with LSTID observations in storms of similar magnitudes. We demonstrate the LSTIDs reach altitudes beyond the topside ionosphere with amplitudes of <5% over background which will facilitate the use of plasma measurements from the topside ionosphere to supplement measurements from GNSS in the study of TIDs. Additionally, we demonstrate the dependence of the characteristics of these TADs and TIDs on longitude.

It is well-known that equatorial plasma bubbles (EPBs) are highly correlated to the post-sunset rise of the ionosphere on a climatological basis. However, when proceeding to the daily EPB development, what controls the day-to-day/longitudinal variability of EPBs remains a puzzle. In this study, we investigate the underlying physics responsible for the day-to-day/longitudinal variability of EPBs using the Sami3 is A Model of the Ionosphere (SAMI3) and the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X). Simulation results on October 20, 22, and 24, 2020 were presented. SAMI3/WACCM-X self-consistently generated midnight EPBs on October 20 and 24, displaying irregular and regular spatial distributions, respectively. However, EPBs are absent on October 22. We investigate the role of gravity waves on upwelling growth and EPB development and discuss how gravity waves contribute to the distributions of EPBs. Of particular significance is that we found the westward wind associated with solar terminator waves and gravity waves causes midnight vertical drift enhancement and collisional shear instability, which provides conditions favorable for upwelling growth and EPB development. The converging and diverging winds associated with solar terminator waves and midnight temperature maximum also affect the longitudinal distribution of EPBs. The absence of EPBs on October 22 is related to the weak upward drift induced by weak westward wind associated with solar terminator waves.

A linear theory of the generalized Rayleigh-Taylor instability (GRTI) is derived which includes ion inertia and acceleration forces, as well as E region drivers: the zonal neutral wind and plasma drift. This is in contrast to the F region drivers aside from gravity: the meridional neutral wind and the meridional/vertical plasma drifts. Both a local theory and a flux-tube integrated theory are presented with application to the onset of ionosphere irregularities associated with equatorial spread F. Inertia and acceleration forces do not affect the growth rate of the GRTI for nominal ionospheric conditions, but the E region zonal drifts can significantly increase or decrease the growth rate of the GRTI in the equatorial and mid-latitude ionosphere depending on their direction.

We present a method for estimating incident photoelectrons’ energy spectra as a function of altitude by combining global scale far-ultraviolet (FUV) and radio-occultation (RO) measurements. This characterization provides timely insights important for accurate interpretation of ionospheric parameters inferred from the recently launched Ionospheric Connection Explorer (ICON) observations. Quantification of photoelectron impact is enabled by the fact that conjugate photoelectrons (CPEs) directly affect FUV airglow emissions but not RO measurements. We demonstrate the technique for the estimation of photoelectron fluxes and their spectra by combining coincident ICON-FUV and COSMIC2 measurements and show that a significant fraction of ICON-FUV measurements are affected by CPEs during the winter solstice. A comparison of estimated photoelectron fluxes with the SAMI2-PE model is used to gain further insights into the estimation method and reveals consistent values at low latitudes, while the results suggest that the model might be overestimating photoelectron fluxes by $\sim$10\% at mid latitudes.

The energy deposition from ring current ions into the high density “cold” plasma of the ionosphere and plasmasphere is analyzed, based on a Comprehensive Inner Magnetosphere-Ionosphere (CIMI) simulation of the 2015 October 7 storm. In this re-examination of ring current heating generating the observed O$^+$ shell in the outer plasmasphere [1], the Naval Research Laboratory (NRL) Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/plasmasphere code [2] is used to simulate the effect of ring current heating on the ionosphere. We find that energy is deposited at altitudes as low as 100 km. We show that heating along the entirety of any given field line, both in the ionosphere and plasmasphere, contributes to the heating effect and subsequent cold O$^+$ outflows. We further show that, relative to the heating of the plasmasphere, the direct heating of the ionosphere by ring current ions produces only a small contribution to the thermal O$^+$ outflow that forms the O$^+$ shell. [1] Krall, J., J. D. Huba, and M.-C. Fok (2020), Does ring current heating generate the observed O$^+$ shell?, Geophys. Res. Lett., 47, e2020GL088419, doi:10.1029/2020GL088419 [2] Huba, J., and J. Krall (2013), Modeling the plasmasphere with SAMI3, Geophys. Res. Lett., 40, 6–10, doi:10.1029/2012GL054300 Research supported by NRL base funds and NASA.

Simultaneous measurements of F-region neutral winds near 250 km and topside interhemispheric plasma flow near 600 km, made by the ICON satellite, allow the connection between these parameters to be observationally established for the first time. The largest variations in the topside plasma flows are seen as a function of season and are shown to depend on trans-equatorial neutral winds below the F peak in a manner that is essentially the same during the daytime and the nighttime for the solar minimum conditions that prevail in 2020. This finding is consistent with established principles of a servo model of the ionosphere for which both production and loss rates in the topside are specified by the O/N2 ratio at the F-peak height. The intermediate relationships, describing how the neutral wind influences the F-peak height and how the O+ plasma pressure gradient across the equator influences the interhemispheric plasma flow are also investigated and found to be consistent with expectations.