Ionospheric Observations Research Articles

Mitigation of Short-Term Temporal Variations of Receiver Code Bias to Achieve Increased Success Rate of Ambiguity Resolution in PPP

Ambiguity resolution (AR) is critical for achieving a fast, high-precision solution in precise point positioning (PPP). In the standard uncombined PPP (S-UPPP) method, ionosphere-free code biases are superimposed by ambiguity and receiver clock offsets to be estimated. However, besides the time-constant part of the receiver code bias, the complex and time-varying term in receivers destroy the stability of ambiguities and degrade the performance of the UPPP AR. The variation of receiver code bias can be confirmed by the analysis in terms of ionospheric observables, code multipath (MP) of the Melbourne–Wübbena (MW) combination and the ionosphere-free combination. Therefore, the effect of receiver code biases should be rigorously mitigated. We introduce a modified UPPP (M-UPPP) method to reduce the effects of receiver code biases in ambiguities and to decouple the correlation between receiver clock parameters, code biases, and ambiguities parameters. An extra receiver code bias is set to isolate the code biases from ambiguities. The more stable ambiguities without code biases are expected to achieve a higher success rate of ambiguity resolution and a shortened convergence time. The variations of the receiver code biases, which are the unmodeled errors in measurement residuals of the S-UPPP method, can be estimated in the M-UPPP method. The maximum variation of the code biases is up to 16 ns within two-hour data. In the M-UPPP method, the averaged epoch residuals for code and phase measurements recover their zero-mean features. For the ambiguity-fixed solutions in the M-UPPP method, the convergence times are 14 and 43 min with 17.7% and 69.2% improvements compared to that in the S-UPPP method which are 17 and 90 min under the 68% and 95% confidence levels.

Initial nighttime ionospheric observations with advanced ionospheric probe onboard FORMOSAT-5

FORMOSAT-5 satellite was launched into a sun-synchronous orbit at 720 km altitude with 98.28° inclination on 25 August 2017. The onboard scientific payload, Advanced Ionospheric Probe (AIP) is capable of measuring topside ionospheric ion density, cross-track flow velocities, ion composition and temperature, and electron temperature. Initial observations of nighttime midlatitude ionospheric density and vertical flow velocity variations at 2230 LT sector during a few quiet magnetic days in December 2017 are studied here. Longitudinal density variations in the equatorward edge of midlatitude ionospheric trough (MIT) region are noticed. Accompanied with this density variation, the vertical flow velocities also behave differently. Although the density difference has been stated due to zonal wind effect related to the declination of the geomagnetic field lines, the vertical flow velocity variation seems to play the opposite role. All these density and vertical flow observations in the northern winter hemisphere can only be explained by the longitudinal differences in the diffusion velocity coming down from the protonsphere (plasmasphere). In addition, the hemispheric asymmetry in the vertical flow velocity can also be explained by the interaction between the topside ionosphere and the protonsphere. The observed vertical flow variations near MIT at different longitudes should present a new potential tool for the study of MIT formation.

Mitigation of receiver biases in ionospheric observables from PPP with ambiguity resolution

PPP (Precise Point Positioning) is a GNSS (Global Navigation Satellite Systems) positioning method that requires SSR (State Space Representation) corrections in order to provide solutions with an accuracy of centimetric level. The so-called RT-PPP (Real-time PPP) is possible thanks to real-time precise SSR products, for orbits and clocks, provided by IGS (International GNSS Service) and its associate analysis centers such as CNES (Centre National d'Etudes Spatiales). CNES SSR products also enable RT-PPP with integer ambiguity resolution. In GNSS related literature, PPP with ambiguity resolution (PPP-AR) in real-time is often referred as PPP-RTK (PPP – Real Time Kinematic). PPP-WIZARD (PPP - With Integer and Zero-difference Ambiguity Resolution Demonstrator) is a software that is made available by CNES. This software is capable of performing PPP-RTK. It estimates slant ionospheric delays and other GNSS positioning parameters. Since ionospheric effects are spatially correlated by GNSS data from active networks, it is possible to model and provide ionospheric delays for any position in the network coverage area. The prior knowledge ionospheric delays can reduce positioning convergence for PPP-RTK users. Real-time ionospheric models could benefit from highly precise ionospheric delays estimated in PPP-AR. In this study, we demonstrate that ionospheric delays obtained throughout PPP-AR estimation are actu ally ionospheric observables. Ionospheric observables are biased by an order of few meters caused by the receiver hardware biases. These biases prohibit the use of PPP-WIZARD ionospheric delays to produce ionospheric models. Receiver biases correction is essential to provide ionospheric delays while using PPP-AR based ionospheric observables. In this contribution, a method was implemented to estimate and mitigate receiver hardware biases influence on slant ionospheric observables from PPP-AR. In order to assess the proposed approach, PPP-AR data from 12 GNSS stations were processed over a two-month period (March and April 2018). A comparison between IGS ionospheric products and PPP-AR based ionospheric observables corrected for receiver biases, resulted in a mean of differences of −39 cm and 51 cm standard deviation. The results are consistent with the accuracy of the IGS ionospheric products, 2–8 TECU, considering that 1 TECU is ~16 cm in L1. In another analysis, a comparison of ionospheric delays from 5 pairs of short baselines GNSS stations found an agreement of 0.001 m in mean differences with 22 cm standard deviation after receiver biases were corrected. Therefore, the proposed solution is promising and could produce high quality (1–2 TECU) slant ionospheric delays. This product can be used in a large variety of modeling approaches, since ionospheric delays after correction are unbiased. These results indicate that the proposed strategy is promising, and could benefit applications that require accuracy of 1–2 TECU (~16–32 cm in L1).

IDEASSat: A 3U CubeSat mission for ionospheric science

The Ionospheric Dynamics Exploration and Attitude Subsystem Satellite (IDEASSat/ INSPIRESat-2) is a three-unit (U) CubeSat developed with the objective of providing in-situ measurements of the Earth’s ionosphere in order to quantify both global scale ionospheric variability and small scale irregularities. The science payload is the Compact Ionospheric Probe (CIP) - an all in one in-situ plasma sensor developed at Taiwan National Central University (NCU), which is the miniaturized version of the larger Advanced Ionospheric Probe (AIP) that is carried and operational aboard the 450 kg FORMOSAT-5 spacecraft. The spacecraft has been developed by NCU in partnership with the International Satellite Program in Research and Education (INSPIRE) consortium, and is funded by the Taiwan National Space Organization (NSPO), Ministry of Science and Technology, and Ministry of Education as part of the first national effort to encourage small satellite development at Taiwan universities. The development of IDEASSat offers students a hands-on opportunity to learn about space science and technology and will work in conjunction with FORMOSAT-5 and INSPIRESat-1 to provide ionospheric observations spanning different altitudes and local times. The IDEASSat spacecraft subsystems are a combination of commercial off the shelf (COTS) and self-developed components designed by NCU in partnership with other INSPIRE member universities. IDEASSat is expected to be launched in late 2020. In this report, we describe the IDEASSat mission and spacecraft design, as well as unique lessons learned as part of the development process.

Advantages of Uncombined Precise Point Positioning with Fixed Ambiguity Resolution for Slant Total Electron Content (STEC) and Differential Code Bias (DCB) Estimation

The determination of slant total electron content (STEC) between satellites and receivers is the first step for establishing an ionospheric model. However, the leveling errors, caused by the smoothed ambiguity solutions in the carrier-to-code leveling (CCL) method, degrade the performance of ionosphere modeling and differential code bias (DCB) estimation. To reduce the leveling errors, an uncombined and undifferenced precise point positioning (PPP) method with ambiguity resolution (AR) was used to directly extract the STEC. Firstly, the ionospheric observables were estimated with CCL, PPP float-ambiguity solutions, and PPP fixed-ambiguity solutions, respectively, to analyze the short-term temporal variation of receiver DCB in zero or short baselines. Then, the global ionospheric map (GIM) was modeled using three types of ionospheric observables based on the single-layer model (SLM) assumption. Compared with the CCL method, the slight variations of receiver DCBs can be obviously distinguished using high precise ionospheric observables, with a 58.4% and 71.2% improvement of the standard deviation (STD) for PPP float-ambiguity and fixed-ambiguity solutions, respectively. For ionosphere modeling, the 24.7% and 27.9% improvements for posteriori residuals were achieved for PPP float-ambiguity and fixed-ambiguity solutions, compared to the CCL method. The corresponding improvement for residuals of the vertical total electron contents (VTECs) compared with the Center for Orbit Determination in Europe (CODE) final GIM products in global accuracy was 9.2% and 13.7% for PPP float-ambiguity and fixed-ambiguity solutions, respectively. The results show that the PPP fixed-ambiguity solution is the best one for the GIM product modeling and satellite DCBs estimation.

Poststorm Thermospheric NO Overcooling?

AbstractA mechanism of the neutral gas density decrease at middle latitudes during the recovery storm phase is discussed. The recently proposed method to retrieve thermospheric parameters from ionospheric observations is used for the analysis of equinoctial, summer, and winter severe magnetic storms. CHAllenging Minisatellite Payload and Swarm neutral gas density observations are used for a comparison. It is shown that storm‐induced atomic oxygen variation is the controlling process. Well‐known F2‐layer storm morphology and the poststorm decrease of neutral gas density reflect the same storm‐induced variations of atomic oxygen abundance in the upper atmosphere. There is no need to attract a new “poststorm NO overcooling” concept to explain the decrease of neutral gas density.

A method of estimating the Martian neutral atmospheric density at 130 km, and comparison of its results with Mars Global Surveyor and Mars Odyssey aerobraking observations based on the Mars Climate Database outputs

Profiles of the Martian dayside ionosphere can be used to derive the neutral atmospheric densities at 130 km, which can also be obtained from the Mars Climate Database (MCD) and spacecraft aerobraking observations. In this research, we explain the method used to calculate neutral densities at 130 km via ionosphere observations and three long-period 130-km neutral density data sets at northern high latitudes (latitudes > 60°) acquired through ionospheric data measured by the Mars Global Surveyor (MGS) Radio Occultation Experiment. The calculated 130-km neutral density data, along with 130-km density data from the aerobraking observations of the MGS and Mars Odyssey (ODY) in the northern high latitudes, were compared with MCD outputs at the same latitude, longitude, altitude, solar latitude, and local time. The 130-km density data derived from both the ionospheric profiles and aerobraking observations were found to show seasonal variations similar to those in the MCD data. With a negative shift of about 2 × 1010 cm−3, the corrected 130-km neutral densities derived from MCD v4.3 were consistent with those obtained from the two different observations. This result means that (1) the method used to derive the 130-km neutral densities with ionospheric profiles was effective, (2) the MCD v4.3 data sets generally overestimated the 130-km neutral densities at high latitudes, and (3) the neutral density observations from the MGS Radio Science Experiment could be used to calibrate a new atmospheric model of Mars.

Investigating the foF2 variations at the Ionospheric Observatory of Rome during different solar cycles minimums and levels of geomagnetic activity

The variations of the hourly observations of the critical frequency foF2, recorded at the Ionospheric Observatory of Rome by the AIS-INGV ionosonde (geographic coordinates 41.82° N, 12.51° E; geomagnetic coordinates 41.69° N, 93.97° E) during the low activity periods at the turn of solar cycles 21–22, 22–23 and 23–24, are investigated. Deviations of foF2 greater than ± 15% with respect to a background level, and with a minimum duration of 3 h, are here considered anomalous. The dependence of these foF2 anomalies on geomagnetic activity has been accurately investigated. Particular attention has been paid to the last deep solar minimum 2007–2009, in comparison with the previous solar cycle minima. The lack of day-time anomalous negative variations in the critical frequency of the F2 layer, is one of the main findings of this work. Moreover, the analysis of the observed foF2 anomalies confirms the existence of two types of positive F2 layer disturbances, characterised by different morphologies and, different underlying physical processes. A detailed analysis of four specific cases allows the definition of possible scenarios for the explanation of the mechanisms behind the generation of the foF2 anomalies.

Ionospheric Anomaly Detection to Support the BDSBAS

Corrections and integrity bounds of the ionospheric delay generated at the Satellite-Based Augmentation System (SBAS) for aviation users may confront a wide range of ionospheric conditions over its update interval. Ionospheric irregularities affecting Single Frequency (SF) SBAS can cause the risk of service integrity and a loss of service continuity. The aim of the Ionospheric Anomaly Detection (IAD) scheme is to detect the effect of ionospheric irregularities on the SBAS SF service operational capability over China. It will help in establishing statistical anomaly models and then provides a high level of service for aviation users. The IAD scheme uses a fusion protocol to reach consensus among subdetectors, which monitor different ionospheric features. Moreover, the threshold of every sub-detector is derived based on system availability. We analyze the IAD scheme by practical ionosphere observations recorded at the crustal movement observation network of China in 2015. It successfully identifies ionospheric anomalies affecting SF SBAS and conforming with physical characteristics. Furthermore, it provides sufficient detection reliability. The statistical results illustrate that the difference of 95% residual error for post-ionosphere correction between normal and anomalous zones is between 1.4 m and 3.2 m. The average value is 2.1723 m. Additionally, there exist two types of ionospheric anomalies affecting SBAS SF service over China. The range is mainly at latitude 15°-35°N. The occurrence time is mainly at GPS time 4-15 h and 12-19 h, respectively.

The Contribution of Flux Transfer Events to Mercury's Dungey Cycle

AbstractBursty dayside reconnection plays a proportionally larger role in the driving of Mercury's magnetosphere than it does at Earth. Individual bursts of reconnection, called flux transfer events (FTEs), are thought to open up to 5% of Mercury's polar cap; coupled with the much higher repetition rate of FTEs at Mercury and the short Dungey cycle timescale, this makes FTEs the major driver of Mercury's magnetosphere. However, comparison between spacecraft and ionospheric observations at Earth suggests that the terrestrial contribution of FTEs may have been severely underestimated, by making implicit assumptions about FTE structure. In this study, we consider the implications of removing these assumptions at Mercury; by considering FTE mechanisms based on longer reconnection lines, we find that the contribution of FTEs to Mercury's Dungey cycle could be 5 times greater than previously thought and that FTEs may be able to provide sufficient flux transport to drive Mercury's substorm cycle.

Preface of the special issue "From the Sun to the Earth’s Interior"

The International Association of Geomagnetism and Aeronomy (IAGA; one of the eight Associations of the International Union of Geodesy and Geophysics, IUGG) is concerned with the understanding and knowledge that result from studies of the magnetic and electrical properties of the Earth's core, mantle and crust, of the middle and upper atmosphere, of the ionosphere and the magnetosphere, of the Sun, the solar wind, the planets and interplanetary bodies and their possible interconnections. Research activities in these fields are developed in Italy at several universities and major national research organizations, such as Istituto Nazionale di Geofisica e Vulcanologia (INGV), Istituto Nazionale di Astrofisica (INAF), Consiglio Nazionale delle Ricerche (CNR); these activities are usually conducted in the frame of international projects and collaborations. The IAGA Italian Committee (U. Villante, National Delegate, University of L'Aquila; L. Vigliotti, Vice-Delegate, CNR/ISMAR, Bologna; F. Berrilli, University of Tor Vergata; R. Bruno, INAF-IAPS; L. Cafarella, INGV; G. Consolini, INAF-IAPS; A. De Santis, INGV; M. Pezzopane, INGV; A. Siniscalchi, University of Bari), in cooperation with INGV, CNR and Area di Ricerca in Astrogeofisica, organized the National Conference From the Sun to the Earth’s Interior (21-22 February, 2018) with the specific intent to stimulate the participation of young researchers, their mutual knowledge, the possibility to meet and discuss with more experienced researchers. To this end, the Committee has also provided a prize for the best scientific contributions presented by young researchers. The Conference was attended by about eighty researchers who discussed themes and presented results in the sectors in which IAGA operates, with both oral and poster contributions. Some of the papers presented during the Conference are collected in this special issue. They deal with a variety of subjects. Some studies have analysed magnetic field measurements with different time resolutions, from milliseconds to hours, to locate the position of polar cusp (Marzocchetti et al., 2019), to reconstruct the plasmaspheric cold plasma density distribution (Del Corpo et al., 2019), to analyze the effects on the ground generated by the geomagnetically induced currents during the occurrence of geomagnetic storms (Tozzi et al., 2019), to study the scaling properties of the geomagnetic field’s spatial fluctuations at both high latitudes (in the Northern and Southern Hemisphere) and low and mid latitudes (De Michelis et al., 2019), but also to investigate, along with electric field measurements, the anomalous electromagnetic signals generated in response to the propagation of a mechanical perturbation within the subsoil (Balasco et al., 2019). Magnetic measurements are also used by Ghezzi et al. (2019) to perform an analysis of the errors that affect magnetic anomaly data as regards the archaeological geophysics. Other studies are instead based on ionospheric measurements to investigate how the F2-layer critical frequency varied over Rome during the last three solar minima (Ippolito, 2019), to study both the dynamical properties of the electron density and the scaling properties of the electron density fluctuations at high latitudes in response to changes in the geomagnetic activity (Giannattasio et al., 2019), and to carry out an interhemispheric comparison between high-latitude ionospheric observations in response to peculiar solar wind conditions (D’Angelo et al., 2019). Floating potential time series measured by the DEMETER satellite are instead used by Materassi et al. (2019) to characterise plasma irregularities in the equatorward boundary of the auroral oval, relying on the recently proposed ALIF method. Last but not least, a statistical approach for the computation of kinematic propagation of interplanetary coronal mass ejections has been developed and presented in order to forecast in real-time their propagation and arrival at Earth (Del Moro et al., 2019). The hospitality of the INGV, the support of the Area di Ricerca in Astrogeofisica, and the endorsement of the CNR are gratefully acknowledged. Thanks are also due to the Editorial board of Annals of Geophysics for the publication of this volume dedicated to the Conference. The Editors G. Consolini, INAF-IAPS, Roma, Italy P. De Michelis, INGV, Roma, Italy M. Pezzopane, INGV, Roma, Italy U. Villante, University of L'Aquila, L’Aquila, Italy

The intensification of metallic layered phenomena above thunderstorms through the modulation of atmospheric tides

We present a multi-instrument experiment to study the effects of tropospheric thunderstorms on the mesopause region and the lower ionosphere. Sodium (Na) lidar and ionospheric observations by two digital ionospheric sounders are used to study the variation in the neutral metal atoms and metallic ions above thunderstorms. An enhanced ionospheric sporadic E layer with a downward tidal phase is observed followed by a subsequent intensification of neutral Na number density with an increase of 600 cm−3 in the mesosphere. In addition, the Na neutral chemistry and ion-molecule chemistry are considered in a Na chemistry model to simulate the dynamical and chemical coupling processes in the mesosphere and ionosphere above thunderstorms. The enhanced Na layer in the simulation obtained by using the ionospheric observation as input is in agreement with the Na lidar observation. We find that the intensification of metallic layered phenomena above thunderstorms is associated with the atmospheric tides, as a result of the troposphere-mesosphere-ionosphere coupling.

Ionospheric Response to Disturbed Winds During the 29 October 2003 Geomagnetic Storm in the Brazilian Sector

AbstractModeling the ionosphere during disturbed periods is one of the most challenging tasks due to the complexity of the phenomena that affect the electric fields and the whole thermosphere environment. It is well known that both, prompt penetration electric fields and large amounts of energy deposited in the polar region during disturbed periods, produce significant disturbances in the global electron density distribution, in particular, in the equatorial ionization anomaly development. Besides, the disturbance dynamo, traveling atmospheric disturbances, and traveling ionospheric disturbances also affect the equatorial ionization anomaly density distribution. In this work we use the Sheffield University Plasmasphere‐Ionosphere Model at Instituto Nacional de Pesquisas Espaciais, to simulate the drastic effects that were observed at the low‐latitude ionosphere in the Brazilian region during a very intense magnetic storm event, the so‐called 2003 Halloween storms. In the absence of measured vertical drift during the storm, a new vertical drift deduced from the interplanetary electric field combined with the time variation of the F region virtual height is used as input. The simulation results showed that, in the case of the disturbed thermospheric wind, the ionospheric observations are better explained when a novel traveling wave‐like disturbance propagating from north to south, at a velocity equal to 300 m/s, is considered.

Potential Application of 205-MHz Stratosphere–Troposphere Wind Profiling Radar in Ionospheric Studies: Preliminary Results

A state-of-the-art 205-MHz wind profiling radar designed for measuring both the horizontal and vertical wind components from 315 m to beyond 20 km has been installed at the Cochin University of Science and Technology (CUSAT), India (10.04°N, 76.33°E, dip angle ~7.1°N). Subsequently, the radar was operated with special configuration to probe the ionosphere. After a series of experiments, the radar was successfully configured to receive ionospheric reflections from about 90 to 500 km range covering the E and F layers, with high resolution (45 m for the 90-110 km region). The received echoes are identified as signatures of field-aligned irregularities (FAIs) of the E and F regions of the ionosphere. The E region echoes were observed at an altitude range of 90-110 km. Both continuous and quasi-periodic structures were identified. Further analysis from the spectrum shows that the E region FAIs are Type 2 in nature. The night time spread-F observed so far is of either bottom type or bottom side in nature. This letter portrays the scope of employing 200 MHz range of very high frequency (VHF) band for ionospheric observations, and the technical details and the initial results of the experiment conducted with this stratosphere-troposphere (ST) Radar.

Infrasonic Wave‐Induced Variations of Ionospheric HF Sounding Echoes

AbstractWe conducted ionospheric observations during several Orbital Corporation International Space Station Resupply missions from the Mid‐Atlantic Regional Spaceport at National Aeronautics and Space Administration Wallops Flight Facility in Virginia. These observations were made under different ionospheric and thermospheric conditions using different variations of an experimental sounding mode of the Wallops Vertical Incidence Pulsed Ionospheric Radar. We present an analysis of variations in signal strength (fading), range (signal delay), and echo arrival angle as the rocket‐generated High Altitude Acoustic Waves propagate in the thermosphere and through the plasma layers being observed. The results improve our understanding of the effects of infrasonic waves on remote sensing of the ionosphere and on radio wave propagation through the ionosphere and thermosphere.

Ionospheric storm of September 2017 observed at ionospheric station Pruhonice, the Czech Republic

The ionospheric effects induced by the September 2017 storm have been exceptional compared to other events in the solar cycle 24. This paper gathers results of the ionospheric observations at the European middle latitude station Pruhonice. It consists of evaluation of ionospheric vertical and oblique sounding, Digisonde drift measurement, and data obtained from the Continuous Doppler Sounding System. We observed strong ionospheric response with an unusual stratification of ionospheric layers, Large Scale Traveling ionospheric disturbances, changes in electron density, and increase and oscillations in plasma drift velocity.

Method for Approximating Field-Line Curves Using Ionospheric Observations of Energy-Variable Electron Beams Launched From Satellites

Using electron beam accelerators attached to satellites in Earth orbit, it may be possible to measure arc length and curvature of field-lines in the inner magnetosphere if the accelerator is designed with the capability to vary the beam energy. These measurements would be very useful in constraining the magnetic field of the inner magnetosphere. For the purpose of properly applying these constraints, a new three step data assimilation modeling approach is discussed. The first step in the procedure would be to use prior information to obtain an initial forecast of the inner magnetosphere. Then, a general curve would be defined that satisfies the observed geometric attributes measured by the experiments, and the prior forecast would then be used to optimize the curve with respect to the allowed degrees of freedom. Finally, this approximation of the field-line would be used to improve the initial forecast of the inner magnetosphere, resulting in a description of the system that is optimally consistent with both the prior information and the measured curvature and arc length. This article details the method by which a family of possible approximations of the field-line may be defined, which is central to the three step approach.

Real-Time Geophysical Applications with Android GNSS Raw Measurements

The number of Android devices enabling access to raw GNSS (Global Navigation Satellite System) measurements is rapidly increasing, thanks to the dedicated Google APIs. In this study, the Xiaomi Mi8, the first GNSS dual-frequency smartphone embedded with the Broadcom BCM47755 GNSS chipset, was employed by leveraging the features of L5/E5a observations in addition to the traditional L1/E1 observations. The aim of this paper is to present two different smartphone applications in Geoscience, both based on the variometric approach and able to work in real time. In particular, tests using both VADASE (Variometric Approach for Displacement Analysis Stand-alone Engine) to retrieve the 3D velocity of a stand-alone receiver in real-time, and VARION (Variometric Approach for Real-Time Ionosphere Observations) algorithms, able to reconstruct real-time sTEC (slant total electron content) variations, were carried out. The results demonstrate the contribution that mass-market devices can offer to the geosciences. In detail, the noise level obtained with VADASE in a static scenario—few mm/s for the horizontal components and around 1 cm/s for the vertical component—underlines the possibility, confirmed from kinematic tests, of detecting fast movements such as periodic oscillations caused by earthquakes. VARION results indicate that the noise level can be brought back to that of geodetic receivers, making the Xiaomi Mi8 suitable for real-time ionosphere monitoring.

Longitudinal variations in thermospheric parameters under summer noontime conditions inferred from ionospheric observations: A comparison with empirical models

Longitudinal variations in the thermospheric neutral composition ([O] and [N2]) and exospheric temperature Tex have been inferred from June monthly median noontime foF1 and foF2 observations at mid-latitudes to check for consistency with empirical MSIS models. In general, a similarity in longitudinal variations has been demonstrated, and this is interesting, as similar variations were obtained with very different methods and different data sources. Both inferred and MSISE-00 modelled height-integrated O/N2 ratios are comparable to TIMED/GUVI observations only under solar minimum conditions but differ substantially under high solar activity. The retrieved height-integrated O/N2 ratio longitudinal variations are small (∼15%) in comparison to the observed NmF2 variations under high solar activity. The height-integrated O/N2 ratio cannot be incorporated into the F2-layer formation mechanism; therefore, such observations cannot be used for any quantitative interpretation of NmF2 variations.

First Incoherent Scatter Measurements and Adaptive Suppression of Field-Aligned Irregularities by the PANSY Radar at Syowa Station, Antarctic

The Program of the Antarctic Syowa Mesosphere–Stratosphere–Troposphere/Incoherent Scatter (PANSY) radar is a large atmospheric radar located at the Antarctic Syowa Station (69.01°S, 39.59°E). The PANSY radar performed the first incoherent scatter (IS) measurements in the Antarctic region in 2015. Several specific observations were undertaken in 2017 including a 24-h observation of the ionosphere using a peripheral antenna array to suppress interference from the field-aligned irregularities (FAIs). This paper presents the preliminary results derived from the IS measurements using the PANSY radar and the adaptive signal processing techniques to suppress FAIs. The norm-constrained and directionally constrained minimization of power (NC-DCMP) algorithm was applied to the 24-h ionosphere observations by the PANSY radar with a weighting applied to the directional constraint based on the gain differences of the subarrays. When compared with the conventional nonadaptive approach, the number of usable power profiles was increased by about 24% by the gain-weighted NC-DCMP algorithm, suggesting its effectiveness for FAI clutter suppression in ionosphere observations. Furthermore, detection of FAIs using the dedicated antenna array was found valuable in assessing the reliability of estimations of electron density based on VHF-band IS radar data.