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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. Plain Language Summary: 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. Key Points: Validation of Dynasonde analysis (JVD) ion drift velocities by using simultaneous but independent SuperDARN observationsJVD ion velocities are generally in a good agreement with SuperDARN radar observationsSmall‐scale ionospheric density irregularities tends to move with large‐scale plasma contours as the geomagnetic activity increases [ABSTRACT FROM AUTHOR]

Noticeable F‐region electron density (NmF2) depletions were observed in the winter‐nighttime polar cap ionosphere during solar minimum from the Vertical Incidence Pulsed Ionospheric Radar (VIPIR) with Dynasonde analysis at Jang Bogo Station (JBS) in Antarctica. We focus on the F‐region density depletion events (known as polar holes) following a steady quiet condition that is defined with Kp values ≤ 1+ during 6 hr. Forty‐five polar holes were identified by JBS VIPIR/Dynasonde (JVD) in 2019. All of the events started over a wide range of nightside magnetic local time (22‐05 MLT) with a peak occurrence at 01–03 MLT. JVD measured exponential NmF2 decrease in the nightside MLT (∼19–2.5 hr) zone with e‐fold decay times distributed in the range of ∼0.5–∼3.5 hr before the onset of a polar hole. The e‐folding times decrease along the longitude from dusk toward midnight. The horizontal ion drift velocity (Vhor) estimated from JVD monotonically goes down from ∼190 m/s at 18 MLT to ∼100 m/s near magnetic midnight, and the NmF2 is depleted as Vhor decreases prior to the polar hole formation. The observations of the exponential NmF2 decrease and the positive correlation between NmF2 and Vhor prior to the polar holes are discussed in light of possible formation mechanisms of polar holes, including temporal variations and spatial structure of the polar ionosphere. Key Points: Polar holes were mostly observed at ∼22−06 MLT under extremely quiet geomagnetic conditionsExponential electron density decrease occurred ∼1.0−4.5 hr prior to the onset of the polar holesThe exponential declination of NmF2 due to recombination loss is the reason for the formation of the polar holes [ABSTRACT FROM AUTHOR]

Vertical incidence pulsed ionospheric radar (VIPIR) has been operated to observe the polar ionosphere with Dynasonde analysis software at Jang Bogo Station (JBS), Antarctica, since 2017. The JBS-VIPIR-Dynasonde (JVD) provides ionospheric parameters such as the height profile of electron density with NmF2 and hmF2, the ion drift, and the ionospheric tilt in the bottomside ionosphere. The JBS (74.6°S, 164.2°E) is located in the polar cap, cusp, or auroral region depending on the geomagnetic activity and local time. In the present study, an initial assessment of JVD ionospheric densities is attempted by the comparison with GPS TEC measurements which are simultaneously obtained from the GPS receiver at JBS during the solar minimum period from 2017 to 2019. It is found that the JVD NmF2 and bottomside TEC (bTEC) show a generally good correlation with GPS TEC for geomagnetically quiet conditions. However, the bTEC seems to be less correlated with the GPS TEC with slightly larger spreads especially during the daytime and in summer, which seems to be associated with the characteristics of the polar ionosphere such as energetic particle precipitations and large density irregularities. It is also found that the Dynasonde analysis seems to show some limitations to handle these characteristics of the polar ionosphere and needs to be improved to produce more accurate ionospheric density profiles especially during disturbed conditions. [ABSTRACT FROM AUTHOR]

We present the first observations from a new low-cost oblique ionosonde located in Antarctica. The transmitter is located at McMurdo Station, Ross Island, and the receiver at Amundsen–Scott Station, South Pole. The system was demonstrated successfully in March 2019, with the experiment yielding over 30 000 ionospheric echoes over a 2-week period. These data indicate the presence of a stable E layer and a sporadic and variable F layer with dramatic spread F of sometimes more than 500 km (in units of virtual height). The most important ionospheric parameter, NmF2, validates well against the Jang Bogo Vertical Incidence Pulsed Ionospheric (VIPIR) ionosonde (observing more than 1000 km away). GPS-derived TEC data from the Multi-Instrument Data Analysis Software (MIDAS) algorithm can be considered necessary but insufficient to predict 7.2 MHz propagation between McMurdo and the South Pole, yielding a true positive in 40 % of cases and a true negative in 73 % of cases. The success of this pilot experiment at a total grant cost of USD 116 000 and an equipment cost of ∼ USD 15 000 indicates that a large multi-static network could be built to provide unprecedented observational coverage of the Antarctic ionosphere. [ABSTRACT FROM AUTHOR]

We present an empirical model of thermospheric winds (High‐latitude Thermospheric Wind Model [HL‐TWiM]) that specifies F region high‐latitude horizontal neutral winds as a function of day of year, latitude, longitude, local time, and geomagnetic activity. HL‐TWiM represents the large‐scale neutral wind circulation, in geomagnetic coordinates, for the given input conditions. The model synthesizes the most extensive collection to date of historical high‐latitude wind measurements; it is based on statistical analyses of several decades of F region thermospheric wind measurements from 21 ground‐based stations (Fabry‐Perot Interferometers and Scanning Doppler Imaging Fabry‐Perot Interferometers) located at various northern and southern high latitudes and two space‐based instruments (UARS WINDII and GOCE). The geomagnetic latitude and local time dependences in HL‐TWiM are represented using vector spherical harmonics, day of year and longitude variations are represented using simple harmonic functions, and the geomagnetic activity dependence is represented using quadratic B splines. In this paper, we describe the HL‐TWiM formulation and fitting procedures, and we verify the model against the neutral wind databases used in its formulation. HL‐TWiM provides a necessary benchmark for validating new wind observations and tuning our physical understanding of complex wind behaviors. Results show stronger Universal Time variation in winds at southern than northern high latitudes. Model‐data intra‐annual comparisons in this study show semiannual oscillation‐like behavior of GOCE winds, rarely observed before in wind data. Key Points: We developed a comprehensive empirical model of high‐latitude F region thermospheric winds (HL‐TWiM)Universal Time variations in high‐latitude winds are stronger in the Southern than Northern HemisphereHL‐TWiM provides a necessary benchmark for validating new high‐latitude wind observations and tuning first principal models [ABSTRACT FROM AUTHOR]

HIWIND (High altitude Interferometer WIND experiment) is a balloon‐borne Fabry Perot interferometer for daytime thermospheric wind observations. In this paper, we examine the summer polar cap thermospheric winds observed by HIWIND with the RISR‐C (Resolute Incoherent Scatter Radar‐Canada) observed ion drifts and electron densities. We also perform National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model simulations to compare with the HIWIND and RISR‐C observations. The standard Thermosphere Ionosphere Electrodynamics General Circulation Model underestimates the high‐latitude electron density and overestimates the thermospheric winds. The discrepancies between modeled and observed meridional winds are large near midnight and noon. After increasing the energy flux in the polar cap drizzle, the simulated electron density is comparable with the RISR‐C observations. However, large discrepancies with the HIWIND‐observed thermospheric winds persist. The cause of the model versus observation discrepancy in winds is probably due to the processes outside the polar cap. Key Points: HIWIND made first polar cap daytime thermospheric wind observationNormal TIEGCM underestimates the polar electron density and overestimates thermospheric windsHIWIND observed slightly equatorwind near the local noon [ABSTRACT FROM AUTHOR]

Plasma blobs represent plasma density enhancements with respect to ambient plasma. The formation of blobs in low and middle latitudes is understood in association with either equatorial plasma bubbles or medium‐scale traveling ionospheric disturbances (MSTIDs). This study reports four blob events identified from the Swarm satellite observations in 2014. Those blobs show the conjugate property and the alignment in the northwest‐southeast direction in the Northern Hemisphere and southwest‐northeast direction in the Southern Hemisphere. These are the typical characteristics of nighttime MSTIDs. The observation of MSTIDs in the total electron content maps and the absence of bubbles in the equatorial region at the times of the blob detection further support the association of those blobs with MSTIDs. Plain Language Summary: Three distinguishing mesoscale irregularity structures of the electron density in the low and middle latitude ionosphere are plasma bubbles, plasma blobs, and medium‐scale traveling ionospheric disturbances (MSTIDs). Bubbles and blobs are plasma density depletions and enhancements, respectively, with respect to ambient plasma. MSTIDs are a wave‐like modulation of the plasma density. Bubbles and MSTIDs are independent phenomena created by different mechanisms, but the formation of blobs is understood in association with either bubbles or MSTIDs. Our study reports blobs identified from Swarm satellite observations that show some of the characteristics of MSTIDs. Key Points: The observations by the formation flight of Swarm satellites provide information on the spatial structure of plasma blobsBlobs are aligned in the northwest‐southeast and southwest‐northeast directions in the Northern and Southern HemispheresThe conjugate property and alignment support the association of those blobs with medium‐scale traveling ionospheric disturbances [ABSTRACT FROM AUTHOR]

Abstract: During the last decade, the TOPEX/Poseidon mission has provided a wealth of data pertaining to total electron content (TEC) measurements over the oceans, where conventional measurements are sparse. In this study, a comprehensive comparison of the TOPEX TEC measurements with the recent version of the International Reference Ionosphere (IRI-2001) was performed. The study covered solar cycle, seasonal, geomagnetic activity, and longitudinal variations. First, it was found that both the IRI and TOPEX TEC show a negligibly small geomagnetic dependency, regardless of the solar activity and seasonal conditions. For solar activity, however, not only the TECs from the IRI and TOPEX measurements, but also the difference between them, strongly depend on the solar activity. The comparison also shows that the daytime low-latitude ionosphere from the IRI always develops earlier than the corresponding TOPEX measurements, appearing as an overestimate of IRI TEC at around 7 magnetic local time (MLT) in the morning. With respect to the annual and seasonal variations of TEC, the TOPEX TEC shows stronger annual and semiannual anomalies than the IRI TEC both at low latitudes and at upper mid-latitudes. However, the IRI and TOPEX TECs show a similar seasonal anomaly only for high solar activity. Finally, the longitudinal variations of the IRI TEC show good agreement with the TOPEX measurements for low solar activity, but for high solar activity, large discrepancies occur in the Pacific sector. [Copyright &y& Elsevier]

Although the horizontal density structures of the polar ionosphere have been extensively studied mostly using the F-region peak density or total electron content, there are relatively few studies on the vertical density structures. In this review, we present the climatology of the polar ionospheric density not only in the F-region but also in the E-region and topside ionosphere, in comparison with the mid-latitude ionosphere, using long-term incoherent scatter radar (ISR) observations at Millstone Hill, Tromsø, and Svalbard. The ISR data during the period of 1995–2015 are analyzed to study on the variations with local time, season, and solar/geomagnetic activity. The diurnal variations of the F-region density are much smaller in the polar region than in the mid-latitude, particularly in summer. At Svalbard, there is a characteristic double-peak structure in the diurnal variation of the polar ionosphere in winter only for high solar activity. The diurnal variation of hmF2 decreases with increasing latitude and eventually disappears at Svalbard for low solar activity but the hmF2 and its diurnal variations in the polar ionosphere are remarkably enhanced for high solar activity. The distinctive irregularity in the mid-latitude F1-layer nearly disappears in the polar region, especially at Svalbard. The anomalous seasonal variations of the F-region density are less evident in the polar ionosphere especially for low solar activity and for high magnetic activity conditions. The polar E-region density shows characteristic nighttime peaks induced by auroral precipitation but it does not necessarily increase with solar activity. The topside ionospheric density variations are much stronger in the polar region for high solar activity. Finally, it is found that the polar ionospheric density profiles more strongly respond to increasing solar activity as well as the magnetic activity compared with the mid-latitude ionosphere. • Diurnal variation of the polar ionosphere is largely much smaller than the mid-latitude ionosphere. • But hmF2 shows remarkable diurnal variations for high solar activity in the polar region. • Seasonal variations of the ionosphere are less evident and only occur during low magnetic activity in the polar region. • Auroral contribution to the E-region density is largest in winter for low solar activity. • Ionospheric responses to solar and magnetospheric energy inputs are much more complex in the polar region. [ABSTRACT FROM AUTHOR]

The properties of Pi2 pulsations observed in the upper ionosphere are studied using magnetic field data acquired by the Swarm A spacecraft in low Earth orbit and at the low‐latitude Bohyun ground station (BOH, L=1.3) for January 2014 to June 2015. From time intervals when Swarm A was on the nightside (magnetic local time (MLT) = 1800–0600 hr) and the BOH station was near midnight (MLT = 2100–0300 hr), we identified 621 Pi2 events in the horizontal H component of the BOH data. For each event we examined the coherence between the horizontal H component on the ground and the Bx (radial), By (azimuthal), or Bz (compressional) components at Swarm A. Out of 621 events, the Bx−H high‐coherence (> 0.7) events are ∼6%, the By−H high‐coherence events are ∼2%, and the Bz−H high‐coherence events are ∼25%. The ground satellite high‐coherence events occurred when the spacecraft was located at magnetic latitudes between −50° and 50°. Using the ground satellite high‐coherence events, we statistically examined the latitudinal structure of the relative amplitude and phase of the ionospheric Pi2 pulsations and found that their latitudinal variations is consistent with the north‐south mode structure expected from the plasmaspheric resonance model. Our statistical results indicate that the source of ionospheric Pi2 pulsations is the plasmaspheric resonance. Key Points: The ground satellite high coherence occurs when the spacecraft was located at |MLAT| ≤ 50°The latitudinal structure of the relative amplitude and phase of the ionospheric Pi2 pulsations are examinedThe source of ionospheric Pi2 pulsations is the plasmaspheric resonance [ABSTRACT FROM AUTHOR]

We examined wave activities in the Pc5 frequency band (~2–7 mHz) using the magnetic field data from five Antarctic stations, which are AGO3 (72.5° S Altitude-Adjusted Corrected Geomagnetic latitude), South Pole (SPA, 74.6° S), McMurdo (MCM) and Jang Bogo Station (JBS, 80° S), and Dome C (DMC, 89.1° S), during 2017. Pc5 waves at AGO3 and SPA show characteristics associated with Kelvin-Helmohltz instability on the magnetopause and substorm activities, under closed field lines conditions. The local time and seasonal dependence of Pc5 wave activities at polar cap stations (MCM, JBS, and DMC) are significantly different from those at AGO3 and SPA. These indicate that the generation mechanism of Pc5 activities in the open field line region at polar cap is different from that in the closed field lines. We suggest that polar-cap Pc5 is generated by ionospheric current variations produced by solar dynamo between solar wind plasma and geomagnetic field. • Pc5 pulsations observed at high latitude ground stations located in Antarctica in 2017. • Latitudinal dependence of diurnal seasonal variations of Pc5 activities. • The comparison of Pc5 and solar wind speed. • Difference generation mechanism of Pc5 waves at auroral latitudes and polar-cap region. [ABSTRACT FROM AUTHOR]