We study the spatial structure of a polarization jet/Sub‐Auroral Ion Drift (PJ/SAID) based on data from the NorSat‐1 and Swarm satellites during a geomagnetic storm. Observations of plasma parameters ...inside the PJ/SAID are obtained with NorSat‐1 using a system of Langmuir probes with a nominal sampling rate of up to 1 kHz, which allowed measurements with such a high temporal resolution for the first time. A comparative analysis of plasma parameters and electron density spectra inside PJ according to the data from both satellites is presented. Our results show that fluctuations of plasma parameters inside the PJ increase at all scales with increasing geomagnetic activity. Small‐scale irregularities in the PJ are measured in situ down to hundreds of meters. The role of large‐scale effects in the PJ increases in comparison with the small‐scale ones during high geomagnetic activity. The PJ consists of structures ∼0.2° latitude in size within which small‐scale irregularities are present.
Plain Language Summary
Polarization jet (PJ), also known as Sub‐Auroral Ion Drift (SAID), events are fast westward plasma drifts with a narrow latitudinal extent, occurring at subauroral latitudes in the Earth's ionosphere. The decrease in the density of the ionospheric plasma inside PJ/SAID significantly affects the conditions for the propagation of shortwave radio waves, which indicates the practical importance of studying this phenomenon. Despite the importance of using a variety of ground‐based observation facilities for studying and analyzing PJ/SAID properties, as well as developing analytical models and numerical modeling, in situ observations are the most valuable. Such in situ observations can be obtained only with satellites flying through a developing PJ/SAID. Large‐scale features of PJ/SAID are currently well understood, but small‐scale processes within PJ/SAID are practically not studied, and many open questions remain. In this work, we study the small‐scale structures in PJ/SAID during a geomagnetic storm of 20 April 2018, using multi‐instrumental approach involving low‐Earth orbit.
Key Points
Fluctuations of plasma parameters inside the polarization jet (PJ) increase at all scales during higher geomagnetic activity
Small‐scale irregularities inside the PJ are measured in situ down to hundreds of meters
The role of large‐scale effects in the PJ increases in comparison with small‐scale ones with geomagnetic activity
Recent availability of a considerable amount of satellite and ground‐based data has allowed us to analyze rare conjugated events where extremely low and very low frequency waves from the same source ...region are observed in different locations. Here, we report a quasiperiodic (QP) emission, showing one‐to‐one correspondence, observed by three satellites in space (Arase and the Van Allen Probes) and a ground station. The main event was on 29 November 2018 from 12:06 to 13:08 UT during geomagnetically quiet times. Using the position of the satellites we estimated the spatial extent of the area where the one‐to‐one correspondence is observed. We found this to be up to 1.21 Earth's radii by 2.26 hr MLT, in radial and longitudinal directions, respectively. Using simple ray tracing calculations, we discuss the probable source location of these waves. At ∼12:20 UT, changes in the frequency sweep rate of the QP elements are observed at all locations associated with magnetic disturbances. We also discuss temporal changes of the spectral shape of QP observed simultaneously in space and on the ground, suggesting the changes are related to properties of the source mechanisms of the waves. This could be linked to two separate sources or a larger source region with different source intensities (i.e., electron flux). At frequencies below the low hybrid resonance, waves can experience attenuation and/or reflection in the magnetosphere. This could explain the sudden end of the observations at the spacecraft, which are moving away from the area where waves can propagate.
Key Points
We report a quasiperiodic emission showing one‐to‐one correspondence at three satellites and a ground station
We established the spatial extent of QP emissions and possible source using satellite measurements and ray tracing
We found changes in slope and shape of QP elements suggesting different sources or larger source region with overlapping characteristics
A spatially distributed chirp ionosonde records signals scattered by the Earth’s surface at long distances from the emitter, even with relatively low transmitter powers. Experimental studies of the ...ionosphere backscatter sounding (BS) based on the multifunctional chirp ionosonde developed at the Institute of Solar–Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS) have revealed the potential of such systems for diagnosing the propagation medium. With a transmitter power of a few kilowatts, it is possible to obtain high-quality BS ionograms within the maximum single-hop range (3000–4000 km). For the analysis of experimental data, algorithms for calculating the characteristics of BS signals, including the amplitude sweep of the recorded signal, are developed. Methods for diagnosing the decameter radio channel using BS data, which are based on the extraction of the leading edge of the BS signal during the processing and interpretation of ionograms, are elaborated. The results of extraction of the signal leading edge on the ionogram are used to calculate the maximum usable frequencies and characteristics of the oblique propagation trajectories for given radio paths in the sounding sector. Algorithms for inversion of the leading edge of the BS signal into the electron density are implemented.
This paper studies the interaction of internal gravity waves (IGW) with neutral wind using the statistics of traveling ionospheric disturbances (TID) from the Radio Physical Complex of the Institute ...of Solar‐Terrestrial Physics. The complex includes the Irkutsk Incoherent Scatter Radar (IISR), Irkutsk Ionosonde (DPS‐4), and Ekaterinburg HF Radar (EKB). The aim of this study is to give a common explanation for the TID azimuth distributions obtained with the IISR‐ionosonde and HF coherent radar and show that the measurements of 3‐D TID characteristics put into the hands of researchers an important tool to study neutral wind in the thermosphere. The distinctive features of this study are the following: (1) using different TID statistics from independent tools and, correspondingly, independent methods for determining TID characteristics; (2) using the 3‐D TID characteristics for testing the wind‐filtering hypothesis, which allows us to separate the IGW‐induced TIDs from TIDs of other nature and identify three TID types depending on their elevation angles; and (3) using the local time‐azimuth distribution of the TID number for testing the wind‐filtering hypothesis. This study allowed us to conclude that the observed IGW azimuth anisotropy can be mainly explained by the wind filtration mechanism with considering winds at 90–250 km heights. Using the 3‐D IGW characteristics allows us to estimate neutral wind parameters. Proposed methods are applicable for any tool which can obtain TID 3‐D characteristics. Using the proposed methods will enable us to organize a worldwide campaign to improve the existing neutral wind models.
Key Points
At least 60% of observed TID induced by IGW; TID LT‐azimuth distributions can be mainly explained by the wind filtration mechanism
There are differences between azimuth distributions of three TID types (source below, source above, and reflected)
Methods of neutral wind estimating were proposed
We developed a method and programs for estimation of the global electron content (GEC) from GPS measurements, using the ionosphere models IRI-2001 and NeQuick. During the 23rd cycle of solar ...activity, the value of GEC varied from 0.8 to 3.2×1032 electrons, following changes in the solar extreme ultra violet (EUV) radiation and solar radio emission at 10.7-cm wavelength. We found a strong resemblance of these variations, with discernible 11-year and 27-day periodicities. A saturation effect of GEC is found when F10.7 increases. We found that GEC is characterized by strong seasonal (semiannual) variations with maximum relative amplitude at about 10% during the rising and falling parts of the solar activity and up to 30% during the period of maximum. It was found that the relative difference between model and experimental GEC series increase as the smoothing time window decreases. We found that GEC-IRI seasonal variations are out-of-phase with experimental GEC values. The lag between model and experimental maximum of GEC values can reach several tens of days. The variations of GEC lag, on average, 2 days after those of F10.7 and UV. GEC completely reflects the dynamics of the active regions on the solar surface. The amplitude of the 27-day GEC variations decreases from 8% at the rising and falling solar activity to 2% at the maximum and at the minimum. We also found that the lifetime of contrast long-living active formations on the Sun's surface in EUV range for more than 1 month exceeds the one in radio range (10.7 cm).
Using the representative statistics on traveling ionospheric disturbances (TIDs) obtained by Yekaterinburg and Magadan radars, we have shown that distributions of TIDs and average TID velocities by ...azimuths and local time agree well with the hypothesis on internal gravity wave (IGW) filtering by the neutral wind. We have examined the influence of significant winter sudden stratospheric warmings on IGW in the ionosphere. A method has been proposed for estimating zonal and meridional neutral wind velocities from MSTID parameters. The method is universal and allows us to estimate the zonal and meridional neutral wind velocities from the statistics on MSTID 2D phase velocity vector obtained by any tool. There is a large amount of data from which MSTID 2D phase velocity vector (as opposed to the 3D phase velocity vector) can be derived, including maps of TEC disturbances and all-sky camera images. This method may therefore be useful in developing and improving neutral wind models.
We present a multi‐instrumental study of ionospheric irregularities of different scales (from tens of centimeters to few kilometers) observed over the Central and East Siberia, Russia, during a ...moderate‐to‐strong geomagnetic storm on 27–28 May 2017. From high‐frequency (HF) and ultrahigh‐frequency (UHF) radar data, we observed an intense auroral backscatter developed right after the initial phase of the geomagnetic storm. Additionally, we examined variations of Global Positioning System (GPS)‐based ROT (rate of TEC changes, where TEC is total electron content) for available GPS receivers in the region. Ionosondes, HF, and UHF radar data exhibited a presence of intense multi‐scale ionospheric irregularities. We revealed a correlation between different‐scale Auroral/Farley‐Buneman ionospheric irregularities of the E layer during the geomagnetic storm. The combined analysis showed that an area of intense irregularities is well connected and located slightly equatorward to field‐aligned currents (FACs) and auroral oval at different stages of the geomagnetic storm. An increase and equatorward displacement of Region 1 (R1)/Region 2 (R2) FACs leads to appearance and equatorward expansion of ionospheric irregularities. During downward (upward) R1 FAC and upward (downward) R2 FAC, the eastward and upward (westward and downward) E × B drift of ionospheric irregularities occurred. Simultaneous disappearance of UHF/HF auroral backscatter and GPS ROT decrease occurred during a prolonged near noon reversal of R1 and R2 FAC directions that accompanied by R1/R2 FAC degradation and disappearance of high‐energy auroral precipitation.
Key Points
Rate of total electron content change, HF, and UHF auroral backscatter revealed similar dynamics during geomagnetic storm
UHF/HF auroral backscatter appeared/disappeared almost simultaneously with field‐aligned currents and particle precipitation increase/decrease
Configuration of R1/R2 field‐aligned currents influence on horizontal and vertical transport of ionospheric irregularities
The analysis of the regular features of the high-, mid- and low-latitude ionosphere characteristics has been carried out using local empirical models. The local empirical models were derived from the ...manual scaled ionogram data recorded by DPS-4 Digisondes located at Norilsk (69N,88E), Irkutsk (52N,104E) and Hainan (19N,109E) for a 6-year period from December, 2002 to December, 2008. The technique used to build the local empirical model is described. Primary focuses are diurnal, seasonal and solar cycle variations of the peak electron density and the peak height under low solar activity and their changes with increasing solar activity. The main objective of the paper is to reveal both common and specific features of high-, mid- and low-latitude ionosphere. Based on earlier comparisons with the International Reference Ionosphere model, we analyze how the common and specific features are reproduced by this model.
The long-duration continuous Irkutsk incoherent scatter radar observations allowed us to collect 337 electron density vertical profiles obtained almost simultaneously with the radar and the COSMIC in ...the radar vicinity. The COSMIC electron density profiles were compared with those from the radar, Digisonde, and the IRI model. The comparison included 4 seasons and 2 solar activity levels (low and moderate). The number of simultaneous cases was ∼10 times more than in the previous incoherent scatter radar comparisons. In the case of the bottomside characteristics (peak density and bottomside electron content), the deviations between the COSMIC and the ground-based facilities data may be interpreted as the COSMIC measurement errors without significant systematic biases and with root-mean-square values that are ∼1.4–1.6 times smaller those that from the IRI model prediction. In the case of the topside characteristics (topside electron content and ionospheric electron content), the IRI model overestimates the COSMIC data by 0.6–0.8tecu on average, and the COSMIC overestimates the Irkutsk incoherent scatter radar data by 1.0–1.1tecu on average. The percentage differences between the radar and COSMIC in the topside electron content can reach 80%. In terms of the root-mean-square deviation, the COSMIC and the radar agree better than each of them agrees with the IRI model.
The long-duration continuous Irkutsk incoherent scatter radar (ISR) measurements allowed us to obtain the monthly averaged height-diurnal variations of the electron density in the 180–600km ...altitudinal range for 4 four seasons (winter, spring, summer, autumn) and for two solar activity levels (low and moderate). Considering these electron density variations as “quiet ionosphere patterns” we compared them with the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) simulations and the International Reference Ionosphere (IRI) predictions. It was found that some observational features revealed from the ISR measurements are reproduced nicely by both the theoretical and empirical models, and some features agree better with the GSM TIP than with IRI. None of the models is able to reproduce a detailed multi-peak behavior of the electron density observed by ISR at ∼300km and above for the spring and autumn under low solar activity, while for the spring the GSM TIP tends to reproduce the morning and daytime peaks at the same local times as they are seen from the ISR observations.
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