A gigantic submarine volcano erupted near Tonga Island on 15 January 2022 generating a tsunami and related atmospheric and oceanic waves across the globe. This violent volcano triggered extreme disturbances just above the volcanic center that reached near Earth’s stratosphere. This geophysical event generated acoustic-gravity waves to propagate upward and induce significant global perturbations and holes in the mesosphere and lower thermosphere (MLT) regions. Here, we study the MLT region’s response to the Tonga-induced perturbations using ground-based Global Positioning System (GPS)-total electron content (TEC) data from GPS receivers spread in the South American continent. The possible propagation mechanism of the Tonga-related ionospheric holes and perturbations mediated by neutral wind-driven dynamo fields, vertical drifts, and the contribution of geomagnetic conditions will also be discussed.

Due to the special geometry of the electric and magnetic fields at the equator, the vertical ExB drift removes plasma from the geomagnetic equator via an equatorial plasma fountain. This process forms the equatorial ionization anomaly (EIA) by creating the crests at/around 20° latitudes on either side of the geomagnetic equator. It has been reported that symmetric/asymmetric structure and latitudinal extent of the EIAs are affected by the electric fields and thermospheric neutral winds. We investigate the long-term trends in the equatorial ionization anomaly (EIA) and associated phenomena over the South American low-latitude region. These long-term analyses help to develop/update the empirical model of various ionospheric parameters. The EIA features are analyzed using the ground-based Global Positioning System (GPS)-total electron content (TEC) data. We also compare the TEC in EIA obtained from the latest International Reference Model (IRI) model with the observed GPS-TEC data for seasons, different levels of solar activity, and geomagnetic conditions. Finally, We discuss the mechanisms, drivers, and impacts of the EIAs in upper atmospheric electrodynamics.

The thermospheric winds play an important role in the vertical and horizontal couplings of the upper atmosphere by modulating neutral and plasma dynamics. A large variety of observation techniques and numerical as well as empirical models have been developed to understand the behavior of thermospheric winds. The Fabry-Perot interferometer (FPI) is a widely used ground- and satellite-based optical instrument for the thermospheric winds observations in the upper atmosphere. Due to solar contamination of the fainter airglow emission during the daytime, most of the ground-based interferometric wind measurements are limited to the nighttime period only. Despite these constraints, the Second‐generation, Optimized, Fabry‐Perot Doppler Imager (SOFDI) is designed for both daytime and nighttime measurements of thermospheric winds from OI 630‐nm emission and is currently operating at the Huancayo, Peru, near the geomagnetic equator. In this study, we present a comparative analysis of the observed SOFDI wind climatological data and several other modeled results including, but not limited to, Horizontal Wind Model 2014 (HWM-14), Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model with and without implementing Prompt Penetration Electric Field (PPEF), Whole Atmosphere Model (WAM), SAMI3 model, and Magnetic mEridional NeuTrAl Thermospheric (MENTAT) model. We examine the relative performances of these models in the context of the direct-measured thermospheric winds. The day and nighttime modeled winds show an excellent agreement with the SOFDI wind data at the equatorial latitude, except for the daytime zonal winds. Further, this analysis gives a comprehensive picture of how well the measured winds provided by the SOFDI instrument and various models represent the features of the equatorial thermosphere. We also investigate and give an overview of the sources, drivers, effects, and possible mechanisms of the wind variability in the low-latitude thermosphere.

The zonal electric field and the meridional neutral wind are the principal drivers that define the geometry and characteristics of the equatorial ionization anomaly (EIA). Here we present the response of the EIA to the variability of the zonal electric field based on measurements of the equatorial electrojet (EEJ) currents and trans‐equatorial neutral winds for the generation and control of the asymmetries of the EIA crests of total electron content (TEC) in the western side of the South American continent. The EEJ strengths are determined using a pair of magnetometers. The 24‐hr trans‐equatorial neutral wind profile is measured using the Second‐Generation, Optimized, Fabry‐Perot Doppler Imager (SOFDI) located near the geomagnetic equator. The EIA is evaluated using TEC data measured by Global Positioning System (GPS) receivers from the Low‐Latitude Ionospheric Sensor Network and several other networks in South America. A physics‐based numerical model, Low‐Latitude Ionospheric Sector, and SOFDI data are used to study the effects of daytime meridional neutral winds on the consequent evolution of an asymmetry in equatorial TEC anomalies during the afternoon and onward for the first time. We find that the configuration parameters such as strength, shape, amplitude, and latitudinal width of the EIAs are affected by the eastward electric field associated with the EEJ under undisturbed conditions. The asymmetries of EIA crests are observed more frequently during solstices and the September equinox than in the March equinox season. Importantly, this study indicates that the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. This result suggests that a precise observation of the latitudinal TEC profile at low latitudes can be used to derive the meridional wind.

This paper presents the interrelationship between the equatorial electrojet (EEJ) strength, Global Positioning System (GPS)-derived total electron content (TEC), and postsunset scintillation from ground observations with the aim of finding reliable precursors of the occurrence of ionospheric irregularities. Mutual relationship studies provide a possible route to predict the occurrence of TEC fluctuation and scintillation in the ionosphere during the late afternoon and night respectively based on daytime measurement of the equatorial ionosphere. Data from ground based observations in the low latitudes of the west American longitude sector were examined during the 2008 solar minimum. We find a strong relationship exists between the noontime equatorial electrojet and GPS-derived TEC distributions during the afternoon mediated by vertical ExB drift via the fountain effect, but there is little or no relationship with postsunset ionospheric scintillation.

Over an extensive period of time, tremendous amount of scientific effort has been committed to the forecasting of equatorial ionospheric scintillations. This study delineates the interrelationship between the equatorial vertical ExB drift, Equatorial Electrojet (EEJ) strength, Global Positioning System (GPS)derived total electron content (TEC) and postsunset scintillation from ground observations with the aim of finding reliable indications of the occurrence of ionospheric irregularities. Data from ground based observations such as magnetometers, ionosondes, GPS receivers and Incoherent Scatter Radars in the low latitudes of the American longitude sector were examined during the 2008-09 solar minimum. The difference between horizontal components (H) of the geomagnetic field (at and off by 6-9 degrees to dip equator) from a pair of magnetometers is a measure of EEJ strengths and this can be used to estimate vertical drifts. Ionosondes and radars data are expected to give a much more accurate measure of the vertical drifts. The electric field controlling EEJ and ExB drifts might determine whether we have favorable condition for the development of postsunset equatorial plasma bubble (EPB) and scintillations or not. The data show a strong relationship between the electric field and GPS-derived TEC. This presentation will also discuss the relationship between daytime equatorial vertical ExB drift and postsunset ionospheric scintillation.

We use angle-resolved photoemission spectroscopy to show that the near-surface electronic structure of a bulk insulating iridate Sr3Ir2O7 lying near a metal-Mott insulator transition exhibits weak metallicity signified by finite electronic spectral weight at the Fermi level. The surface electrons exhibit a spin structure resulting from an interplay of spin-orbit, Coulomb interaction and surface quantum magnetism. Our results shed light on understanding the exotic quantum entanglement and transport phenomena in iridate-based oxide devices.

The Ruddlesden-Popper (RP) series of iridates (Srn+1IrnO3n+1) have been the subject of much recent attention due to the anticipation of emergent physics arising from the cooperative action of spin-orbit (SO) driven band splitting and Coulomb interactions[1-3]. However an ongoing debate over the role of correlations in the formation of the charge gap and a lack of understanding of the effects of doping on the low energy electronic structure have hindered experimental progress in realizing many of the predicted states[4-8] including possible high-Tc superconductivity[7,9]. Using scanning tunneling spectroscopy we map out the spatially resolved density of states in the n=2 RP member, Sr3Ir2O7 (Ir327). We show that the Ir327 parent compound, argued to exist only as a weakly correlated band insulator in fact possesses a substantial 130meV charge excitation gap driven by an interplay between structure, SO coupling and correlations. A critical component in distinguishing the intrinsic electronic character within the inhomogeneous textured electronic structure is our identification of the signature of missing apical oxygen defects, which play a critical role in many of the layered oxides. Our measurements combined with insights from calculations reveal how apical oxygen vacancies transfer spectral weight from higher energies to the gap energies thereby revealing a path toward obtaining metallic electronic states from the parent-insulating states in the iridates.

Neutron diffraction measurements exploring the magnetic and structural phase behaviors of the candidate ${J}_{\mathrm{eff}}=1/2$ Mott insulating iridate Sr${}_{2}$IrO${}_{4}$ are presented. Comparisons are drawn between the correlated magnetism in this single-layer system and its bilayer analog Sr${}_{3}$Ir${}_{2}$O${}_{7}$, where both materials exhibit magnetic domains originating from crystallographic twinning and comparable moment sizes. Weakly temperature-dependent superlattice peaks violating the reported tetragonal space group of Sr${}_{2}$IrO${}_{4}$ are observed, supporting the notion of a lower structural symmetry arising from a high-temperature lattice distortion, and we use this to argue that moments orient along a unique in-plane axis demonstrating an orthorhombic symmetry in the resulting spin structure. Our results demonstrate that the correlated spin order and structural phase behaviors in both single-layer and bilayer Sr${}_{n+1}$Ir${}_{n}$O${}_{3n+1}$ systems are remarkably similar and suggest comparable correlation strengths in each system.

T36. 00014: Low-lying electronic structure and possible intrinsic gap control in J 1/2 Mott insulating perovskite iridate Sr Ir O *