Simultaneous observations of ion drifts and neutral winds have been conducted at Jang Bogo Station (JBS), Antarctica since 2017 using a Dynasonde and a Fabry-Perot Interferometer, respectively. This study presents the results of a comparison between these two measurements to investigate the impacts of ion drifts on neutral winds in the Southern polar cap during winter. The results observationally demonstrate that neutral winds are largely weaker than ion drifts, suggesting that the neutral winds rarely reach a statistical steady-state. However, thermosphere-ionosphere-electrodynamics general circulation model simulations show the opposite trend, significantly underestimating ion drifts. Neutral winds are also found to have different characteristics depending on the magnetic local time sectors, being weaker on the dayside than on the nightside of the polar cap, which is possibly explained if the previous histories of the neutrals before being observed are considered. Additionally, changes in neutral winds due to ion drag are more noticeable in the duskside than in the dawnside due to differences in collision frequency, which is primarily dependent on the diurnal variations of ionospheric density at JBS.

We investigate the neutral wind and semidiurnal tide (SDT) variations in the mesosphere and lower thermosphere (MLT) during two consecutive minor Southern Hemisphere (SH) sudden stratospheric warmings (SSWs) that occurred unusually early in July-August 2024. Zonal and meridional winds from four meteor radar stations at 50-70 degrees S were analyzed. Zonal winds reversed from eastward to westward between 80 and 100 km altitude during both events, showing a more distinct reversal in the second event. The SDT amplitudes increased and exhibited longitudinal differences around the second event. To elucidate the mechanisms responsible, we analyzed ozone observations from Aura/MLS along with MERRA-2 shortwave heating. Positive ozone anomalies at 10 hPa (similar to 32 km) in the SH polar region around each event coincide with enhanced SDT amplitudes from meteor radars. In addition, the shortwave heating rate shows an enhanced 12-hr component at SH high-latitudes above 40 km during these events, supporting an ozone-related radiative contribution to the SDT variability. Using phase-differences from longitudinally separated meteor radars, we estimated the zonal wavenumber. Based on this analysis, we propose that nonlinear interaction between the quasi-16-day zonal wavenumber-2 planetary wave (Q16DW2) and the migrating semidiurnal tide (SW2) contributed to the observed longitudinal differences in SDT amplitude. Furthermore, nonlinear advection associated with Q16DW2-SDT interactions is examined and shows clear longitudinal differences that lead to longitudinal asymmetry in SDT amplitude. These findings show the strong modulation of the SDT by SH SSWs and underscore the combined roles of ozone variability and nonlinear wave interactions in modulating upper-atmospheric tidal responses.

Abstract We analyze the response of mean winds and semidiurnal tides (SDTs) in the mesosphere and lower thermosphere (MLT; ∼70–110 km altitude) to the May 2024 geomagnetic super storm, based on meteor radar (MR) observations from King Sejong Station (KSS; geographic: 62.22°S, 58.78°W; geomagnetic: 53.27°S, 10.88°E) in the Antarctic Peninsula. During the recovery phase of the storm, we observe significant intensifications in both westward and equatorward winds. The SDT amplitude exhibits a marked reduction immediately following the main phase, falling below the 1st percentile of May‐time values derived from 18 years (2007–2024) of long‐term MR observations at KSS. In addition, an enhancement of short‐period oscillations with 3–8 hr periods is accompanied by the decrease in SDT amplitude. As possible generation mechanisms for these oscillations, we discuss the effect of Joule heating with similar periodicities and nonlinear wave interactions during the storm.

This study presents the results from a climatological analysis of thermospheric winds ( 250 km altitude) in the southern polar cap, based on the first long-sterm ground-based Fabry–Perot Interferometer (FPI) observations at Jang Bogo station (JBS; 80°S geomagnetic latitude), Antarctica, during 2014 − 2022. The winds exhibit pronounced diurnal variations, characterized by persistent anti-sunward flow across all magnetic local time sectors with a slight duskward tilt, primarily driven by ion drag in combination with day-to-night pressure gradients. The seasonal and solar activity dependencies show enhanced wind magnitudes during equinoxes and under high solar activity, likely reflecting stronger ion drag from increased ionospheric densities. The wind patterns are further modulated by increasing geomagnetic activity, which intensifies wind speeds and enhances the duskward tilts, associated with the strengthening of the dusk-side ionospheric convection cell. The orientation of the interplanetary magnetic field (IMF) also influences wind behaviors: a negative IMF Bz component increases wind magnitudes, while the IMF By component induces directional asymmetry by modulating ionospheric convection. These results offer new ground-based constraints on thermospheric wind circulation in the southern polar cap and its possible mechanisms over nearly a solar cycle.

This study provides wide coverage for the Pc5 ultra-low frequency discrete spectrum observed in the magnetosphere and high-to-lower latitude ionosphere during noon hours ( 10–14 MLT) on November 4, 2021. During the recovery phase, magnetospheric toroidal mode oscillations (GOES-16 Bn) appeared in response to dayside solar wind dynamic pressure enhancements during high solar wind speeds. At the same time, the super dual auroral radar network at Saskatoon recorded oscillations in both ionospheric line-of-sight velocity and echo power at discrete frequencies of 1.7 and 2.2 mHz (9.8 and 7.5 min). The geomagnetic field components exhibited the same frequency pulsations from high to lower latitudes. The oscillation frequency of the H-component persisted consistently at 1.7 mHz to the lower latitudes. Similar wave oscillations were noticed in the total electron content (TEC) of the Global Positioning System (GPS). The complex demodulation analysis suggests that the observed Pc5 oscillations are consistent with toroidal mode Alfvén waves and field line resonances (FLRs) during the storm recovery phase. The observations indicate a possible association with solar wind dynamic pressure enhancements under high-speed solar wind conditions, while cavity/waveguide modes and magnetopause Kelvin–Helmholtz instability (KHI) may have contributed to the excitation of the observed waves.

Abstract Long‐term observations at southern polar latitudes in the summertime mesosphere–lower thermosphere (MLT) reveal persistent nonmigrating semidiurnal tides, with the zonal wavenumber‐1 ( = 1) component being particularly dominant. Using nearly two decades of meteor radar wind measurements (80–100 km) from Davis Station (East Antarctica) and King Sejong Station (Antarctic Peninsula), we find strong agreement in mean zonal and meridional wind structures and their interannual variability. However, near the summer solstice, the semidiurnal tide exhibits pronounced longitudinal asymmetry: large amplitudes at Davis but weak at King Sejong. This disparity is attributed to interference between the westward‐propagating = 1 and = 2 components, analyzed via singular value decomposition. The decomposed = 1 tide shows interannual variability similar to that of the mean summertime zonal winds, with both variations highly correlated with the size and depth of the Antarctic ozone hole. Modal analysis indicates that, prior to solstice, the = 1 and = 2 tides correspond to the (2,1,4) and (2,2,6) Hough modes, respectively.

We expand the assessment study of modeling capabilities in the prediction of foF2 and hmF2 for the ionospheric climatology (Tsagouri et al., 2018, https://doi.org/10.1029/2018sw002035 ) by using updated empirical (IRI and MIT Empirical model) and physics‐based models (CTIPe, WACCM‐X, and TIE‐GCM) as well as the additional observations in the southern hemisphere. Monthly medians of foF2 and hmF2 are considered to evaluate the model performance for the entire year of 2012. For quantitative evaluation, we employ several metrics including the correlation coefficient ( R ), coefficient of determination ( R 2 ), root‐mean square error (RMSE), mean error (ME), and mean relative error (MRE). The linear regression analysis shows that the empirical models perform much better than physics‐based models for foF2 but to a lesser degree for hmF2. There are negligible hemispheric differences in the predictions from empirical models. All the physics‐based models show relatively good correlations with the observations for foF2 in the northern hemisphere compared to the southern hemisphere, but the hemispheric differences are small for hmF2. The results of the study indicate that recent versions of empirical models tend to perform better than old versions of the models, but this is not always true for physics‐based models.

The electron density profiles produced from the ionospheric sounding system are traditionally estimated by the inversion procedure based on the image analysis of the observed ionograms. Jang Bogo Vertical Incidence Pulsed Ionospheric Radar (VIPIR) with Dynasonde (hereafter, JVD), however, uses the three-dimensional electron density inversion approach named “NeXtYZ” to produce ionospheric density, ion velocity, and tilt of the ionization in the bottomside ionosphere based on the list of detected radio echoes with their physical parameters. Sometimes, the resulting density profiles can be erroneous, not reflecting real ionosphere, probably due to severely disturbed ionosphere in the polar region. In this study, the automatic classification procedure of the estimated electron density profiles is developed to filter out unusable data for the 5-year period from 2017 to 2021. The ionograms are classified into four categories: ‘Unavailable’, ‘Sporadic E’, ‘Needs Reprocessing’, and ‘Available’. It is found that approximately 50% of ionograms are evaluated to be reasonable with proper electron density profiles and about 35% of them tend to be affected by sporadic-E like structures, blocking the F-region ionosphere to be observed. It should be noted that the sporadic-E like structures in the polar ionosphere seems to be main obstacles for the ionospheric sounding observation of the F-region ionosphere. Only less than 10% of ionograms are classified as a reprocessing type which needs to be reprocessed. Finally, no echoes are recognized by Dynasonde analysis for about 5% of ionograms. The reprocessing and/or unavailable types might be associated with auroral precipitations that disturbs the ionosphere in the polar region.

The tip of the Antarctic Peninsula is widely recognized as one of the most active regions for gravity wave activity. Situated in this dynamic area, the King Sejong Station (KSS: 62.22°S, 58.78°W) serves as an ideal location for investigating gravity wave activity in the mesosphere and lower thermosphere (MLT) region. The Korea Polar Research Institute (KOPRI) has been operating a meteor radar (MR) and an airglow all-sky camera (ASC) at KSS for over a decade, enabling studies on gravity wave activity and MLT dynamics. To enhance these observational capabilities, a new optical instrument, the Advanced Mesospheric Temperature Mapper (AMTM), was installed in January 2023. The KSS-AMTM provides hydroxyl (OH) airglow intensities at approximately 87 km altitude as well as two-dimensional temperature maps at a high temporal resolution. This study presents a brief overview of the observational features and operation of the instrument, alongside initial results obtained over 28 clear nights from February to October 2023. As part of the initial validation, observed mesopause temperatures were compared with data from meteor radar and the Microwave Limb Sounder onboard the Aura satellite.

AbstractImpacts of lower atmosphere forecast uncertainties on the Ionosphere‐Thermosphere (IT) system are investigated using the Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere eXtension (WACCM‐X) for April 2010 and March 2013 geomagnetic storms. For each storm, a specified‐dynamics simulation (analysis run) is carried out by constraining the model dynamics using reanalysis data. Results of the analysis runs are used as initial conditions for forecast runs initialized on 20, 10, 5, 2, and 1 day before the storm onset time. The forecast runs show that errors in TEC compared to the analysis run appear in the equatorial region within 1–2 days after forecast starts with differences of about 10%. These discrepancies gradually expand to high‐latitudes after 10 days. These errors in TECs could be due to the deviations in the semidiurnal (SW2) and non‐migrating (DE3) tides that also occur within 1–2 days after forecast starts. SW2 and DE3 tides could modify the E‐region wind driven dynamo at low latitudes, affecting the vertical plasma drift in the F‐region, leading to the forecast errors in TEC. The TEC forecast errors at high‐latitudes could be due to the change in the column integrated O/N2, associated with tidal wind variations and resultant delayed change in vertical motions. The SW2 and DE3 tides can be affected by uncertainties in winds in the mesosphere and lower thermosphere (MLT) in the mid‐to‐high latitudes. The MLT wind uncertainties are correlated with gravity wave drag (GWD), suggesting that the uncertainties in GWD can be one of the major sources of IT forecast errors.

Using the High attitude Interferometer WIND observation balloon and Antarctic Jang Bogo station high latitude conjugate observations of the thermospheric winds we investigate the seasonal and hemispheric differences between the northern and southern hemispheres in June 2018. We found that the summer (northern) hemisphere dayside meridional winds have a double‐hump feature, whereas in the winter (southern) hemisphere the dayside meridional winds have a single hump feature. We attribute that to stronger summer, perhaps, northern hemisphere cusp heating. We also compared the observation with NCAR Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) model. The TIEGCM reproduced the double‐hump feature because of added cusp heating. The summer hemisphere has stronger anti‐sunward winds. This is the first time we have very high latitude conjugate thermospheric wind observations.

Since the installation at the Antarctic Jang Bogo Station (JBS) in 2017, Korea Polar Research Institute (KOPRI) has been operating the Vertical Incidence Pulsed Ionospheric Radar (VIPIR) equipped with Dynasonde analysis (JVD). The two-dimensional ion velocity is one of the key ionospheric parameters obtained from the JVD. The ionospheric ion velocities are compared with simultaneous, but independent, measurements of the Doppler velocity obtained from SuperDARN East radar at Dome C. The JVD ion velocity vector is projected to the line-of-sight direction of the SuperDARN observation over the JBS to be directly compared with each other. The result of comparison shows a reasonable agreement with the correlation coefficient of 0.72. The linear regression coefficient of about 0.5 represents that the JVD ion velocity is generally smaller than the SuperDARN observations by the regression coefficient, which may result from the different height ranges of the measurements. It is also found that the correlation coefficient increases with increasing magnetic activity (Kp), which suggests that the small-scale ionospheric density irregularities tend to move with large-scale plasma motion that is driven by enhanced plasma convection with increasing Kp. The ion drift velocity in the polar ionosphere is one of the key parameters for understanding not only the dynamics of the ionosphere but also the magnetosphere-ionosphere coupling processes and the magnetospheric energy transfer to the neutral atmosphere via ion-neutral interactions. There are several ground-based observational techniques to monitor the ion velocities in the polar region. For example, the incoherent scatter radars (ISRs) can determine the ion motion in the polar region, but usually require expensive resources for their maintenance and operation, which makes them affordable only to large organizations or international consortiums such as EISCAT. Another widely utilized observational system for the ion velocities in the polar region is the SuperDARN radars but they are relatively scarce in Antarctica. The most affordable technique for monitoring the ionosphere is the ionospheric sounding systems capable of observing not only the ionospheric densities but also the ion velocities in the bottomside ionosphere. An advanced sounding system has been operated at Jang Bogo Station in Antarctica since 2017 to produce ionospheric parameters including ion density and velocities. The observed ion velocities are compared with simultaneously observed SuperDARN ion velocities over the JBS and we discuss similarities and differences between the two measurements. Validation of Dynasonde analysis (JVD) ion drift velocities by using simultaneous but independent SuperDARN observations JVD ion velocities are generally in a good agreement with SuperDARN radar observations Small-scale ionospheric density irregularities tends to move with large-scale plasma contours as the geomagnetic activity increases

Korea Polar Research Institute (KOPRI) and Korea Astronomy and Space Institute (KASI) have been participating in the European Incoherent Scatter (EISCAT) Scientific Association as an affiliate institution in order to observe the polar ionosphere since 2015. During the period of December 16–21, 2016 and January 3–9, 2018, the observations for the polar ionospheric parameters such as the electron density profiles, ion drift, and electron/ion temperature are carried out in the polar cap/cusp region by the EISCAT Svalbard radar (ESR). The purpose of the observations is to investigate the characteristic of the winter ionosphere in the dayside polar cap/cusp region. In this paper, we briefly report the results of the ESR observations for winter daytime ionosphere and also the simultaneous observations for the ionosphere-thermosphere system together with the balloon-borne instrument High-Altitude Interferometer WIND Experiment (HIWIND) performed by the High Altitude Observatory (HAO), National Center for Atmospheric Research (NCAR). We further introduce our research activities using long-term EISCAT observations for the occurrence of ion upflow and the climatology of the polar ionospheric density profiles in comparison with the mid-latitude ionosphere. Finally, our future research plans will briefly be introduced.

We conducted a statistical study of polar mesospheric summer echoes (PMSEs) in relation to magnetic local time (MLT), considering the geomagnetic conditions using the K-index (or K). Additionally, we performed a case study to examine the velocity profile, specifically for high velocities (≥ ~100 m/s) varying with high temporal resolution at high K-index values. This study utilized the PMSE data obtained from the mesosphere–stratosphere–troposphere radar located in Esrange, Sweden (63.7°N, 21°E). The change in K-index in terms of MLT was high (K ≥ 4) from 23 to 04 MLT, estimated for the time PMSE was present. During the near-midnight period (0–4 MLT), both PMSE occurrence and signal-to-noise ratio (SNR) displayed an asymmetric structure with upper curves for K ≥ 3 and lower curves for K < 3. Furthermore, the occurrence of high velocities peaked at 3–4 MLT for K ≥ 3. From case studies focusing on the 0–3 MLT period, we observed persistent eastward-biased high velocities (≥ 200 m/s) prevailing for ~18 min. These high velocities were accompanied with the systematic motion of profiles at 85–88 km, including large shear formation. Importantly, the rapid variations observed in velocity could not be attributed to neutral wind effects. The present findings suggest a strong substorm influence on PMSE, especially in the midnight and early dawn sectors. The large zonal drift observed in PMSE were potentially energized by local electromagnetic fields or the global convection field induced by the electron precipitation during substorms.

Abstract Assessing space weather modeling capability is a key element in improving existing models and developing new ones. In order to track improvement of the models and investigate impacts of forcing, from the lower atmosphere below and from the magnetosphere above, on the performance of ionosphere‐thermosphere models, we expand our previous assessment for 2013 March storm event (Shim et al., 2018, https://doi.org/10.1029/2018SW002034). In this study, we evaluate new simulations from upgraded models (the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model version 4.1 and the Global Ionosphere Thermosphere Model (GITM) version 21.11) and from the NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) version 2.2 including eight simulations in the previous study. A simulation from the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model version 2 (TIE‐GCM 2.0) is also included for comparison with WACCM‐X. TEC and foF2 changes from quiet‐time background are considered to evaluate the model performance on the storm impacts. For evaluation, we employ four skill scores: Correlation coefficient (CC), root‐mean square error (RMSE), ratio of the modeled to observed maximum percentage changes (Yield), and timing error (TE). It is found that the models tend to underestimate the storm‐time enhancements of foF2 (F2‐layer critical frequency) and TEC (Total Electron Content) and to predict foF2 and/or TEC better in North America but worse in the Southern Hemisphere. The ensemble simulation for TEC is comparable to results from a data assimilation model (Utah State University‐Global Assimilation of Ionospheric Measurements (USU‐GAIM)) with differences in skill score less than 3% and 6% for CC and RMSE, respectively.

Abstract The main subject of this study is the low‐frequency (with the periods longer than 2 hr) wave processes in the coupled regional system of the Ross Ice Shelf (RIS), the Ross Sea and the atmosphere above them. We investigate possible causal relationships between the wave activity in the three media using a unique set of geophysical instruments: a hydrophone measuring pressure variations on the seafloor, a network of seismometers measuring vertical displacements of the RIS surface, and a Dynasonde system measuring wave characteristics at the ionospheric altitudes. We present an extension of the previously introduced theoretical model of the coupled resonance vibrations of the RIS that quantifies the connection between the ocean tide and the resonance vibrations of the RIS. The ocean tide is confirmed as the most significant source of excitation of the resonances. Analysis of average power spectra in year‐long data sets reveals multiple harmonics of the tide (eight) detected by the RIS seismometers while only three are detected by the seafloor sensor. This may represent a confirmation of the effect of resonance‐related broadband amplification predicted by the model. Several peaks in the spectrum of RIS vibrations have periods different from the periods of nearby tidal constituents and may be associated with broad‐scale resonance RIS vibrations. Resonances may play a role in maintaining the coupled atmosphere‐ocean wave activity. Our results reveal a statistically significant correlation between the spectra of the vertical displacements of the RIS and the spectra of the atmospheric waves.

In the hopes of observing the highest-energy neutrinos (E> 1 EeV) populating the Universe, both past (RICE, AURA, ANITA) and current (RNO-G, ARIANNA, ARA and TAROGE-M) polar-sited experiments exploit the impulsive radio emission produced by neutrino interactions. In such experiments, rare single event candidates must be unambiguously identified above backgrounds. Background rejection strategies to date primarily target thermal noise fluctuations and also impulsive radio-frequency signals of anthropogenic origin. In this paper, we consider the possibility that 'fake' neutrino signals may also be generated naturally via the `triboelectric effect' This broadly describes any process in which force applied at a boundary layer results in displacement of surface charge, leading to the production of an electrostatic potential difference AV. Wind blowing over granular surfaces such as snow can induce such a potential difference, with subsequent coronal discharge. Discharges over timescales as short as nanoseconds can then lead to radio-frequency emissions at characteristic MHz-GHz frequencies. Using data from various past (RICE, AURA, SATRA, ANITA) and current (RNO G, ARIANNA and ARA) neutrino experiments, we find evidence for such backgrounds, which are generally characterized by: (a) a threshold wind velocity which likely depends on the experimental trigger criteria and layout; for the experiments considered herein, this value is typically O(10 m/s), (b) frequency spectra generally shifted to the low-end of the frequency regime to which current radio experiments are typically sensitive (100-200 MHz), (c) for the strongest background signals, an apparent preference for discharges from above-surface structures, although the presence of more isotropic, lower amplitude triboelectric discharges cannot be excluded.

TAROGE-M is a radio antenna array atop $\sim2.7$ km-high Mt.~Melbourne in Antarctica for detecting ultra-high energy (UHE, $E> 10^{17}$ eV) air showers in near-horizontal directions. Besides the detection of cosmic rays and Earth-skimming tau neutrinos, its primary goal is to reproduce the discovery and verify the origin of so-called ANITA anomalous events, having feature of upward-going UHE air showers but cannot be explained by tau neutrinos. The detection concept takes advantages of a high altitude for a broad view toward the horizon; strong and near-vertical geomagnetic field for enhancing the radio signal; and quiet radio environment in Antarctica. Its relatively simple design and high duty cycle make it easily to be extended and thus to achieve an exposure competitive with ANITA experiments within a few years. The first TAROGE-M station operating at 180--450 MHz frequencies deployed in 2020 detected seven UHE cosmic ray events within $25.3$-day livetime. The events have a mean energy of $\sim 1$ EeV and an estimated flux consistent with other experiments, and validate the station as an UHE particle detector. In 2022--2023 season, the system was upgraded for a robust long-term operation, with a more detailed calibration with a drone-borne pulser. We also discuss the planned upgrade, including the implementation of interferometric trigger, which is expected to increase the cosmic ray and tau neutrino acceptances by a factor of 10 at $0.1$ EeV, corresponding to a lower energy threshold by a factor of 3.