High-latitude Ionospheric Irregularities Research Articles

Особенности описания ионосферных неоднородностей высоких широт с помощью ROTI индекса по данным навигационных систем GPS и Transit/Парус

The paper compares the possibilities for describing high latitude ionospheric irregularities with characteristic horizontal scales of several tens of kilometers with ROTI index, based on the reception of GPS and Parus/Transit signals. It is shown that in the case of GPS, the maximum ROTI values are observed in the regions of the auroral oval and polar cap, while for Parus/Transit there is an additional region associated with the field aligned enhancement of phase and TEC fluctuations for observations in the direction of the magnetic zenith. Such differences are associated with the inclinations of the orbits of low-orbit (Parus/Transit) and medium-orbit (GPS) satellites, the latter of which does not effectively scan the magnetic zenith region for receivers located at high latitudes. In addition, there are significant, up to 2 times, differences in the ROTI index values according to GPS and Parus/Transit data, which is associated with different speeds of movement of satellite ionospheric piercing points and their mutual orientation with the plasma drift speed in high latitudes, which can lead to a mismatch in the characteristic horizontal scales of irregularities to which the ROTI index demonstrates maximum sensitivity.

Features of High-Latitude Ionospheric Irregularities Development as Revealed by Ground-Based GPS Observations, Satellite-Borne GPS Observations and Satellite In Situ Measurements over the Territory of Russia during the Geomagnetic Storm on March 17–18, 2015

The dynamic picture of the response of the high- and mid-latitude ionosphere to the strong geomagnetic disturbances on March 17–18, 2015, has been studied with ground-based and satellite observations, mainly, by transionospheric measurements of delays of GPS (Global Positioning System) signals. The advantages of the joint use of ground-based GPS measurements and GPS measurements on board of the Swarm Low-Earth-Orbit satellite mission for monitoring of the appearance of ionospheric irregularities over the territory of Russia are shown for the first time. The results of analysis of ground-based and space-borne GPS observations, as well as satellite, in situ measurements, revealed large-scale ionospheric plasma irregularities observed over the territory of Russia in the latitude range of 50°–85° N during the main phase of the geomagnetic storm. The most intense ionospheric irregularities were detected in the auroral zone and in the region of the main ionospheric trough (MIT). It has been found that sharp changes in the phase of the carrier frequency of the navigation signal from all tracked satellites were recorded at all GPS stations located to the North from 55° MLAT. The development of a deep MIT was related to dynamic processes in the subauroral ionosphere, in particular, with electric fields of the intense subauroral polarization stream. Analysis of the electron and ion density values obtained by instruments on board of the Swarm and DMSP satellites showed that the zone of highly structured auroral ionosphere extended at least to heights of 850–900 km.

High-latitude ionospheric irregularities: differences between ground- and space-based GPS measurements during the 2015 St. Patrick’s Day storm

We present an analysis of ionospheric irregularities at high latitudes during the 2015 St. Patrick’s Day storm. Our study used measurements from ~2700 ground-based GPS stations and GPS receivers onboard five low earth orbit (LEO) satellites—Swarm A, B and C, GRACE and TerraSAR-X—that had close orbit altitudes of ~500 km, and the Swarm in situ plasma densities. An analysis of the rate of TEC index (ROTI) derived from LEO–GPS data, together with Swarm in situ plasma probe data, allowed us to examine the topside ionospheric irregularities and to compare them to the main ionospheric storm effects observed in ground-based GPS data. We observed strong ionospheric irregularities in the topside ionosphere during the storm’s main phase that were associated with storm-enhanced density (SED) formation at mid-latitudes and further evolution of the SED plume to the polar tongue of ionization (TOI). Daily ROTI maps derived from ground-based and LEO–GPS measurements show the pattern of irregularities oriented in the local noon–midnight direction, which is a signature of SED/TOI development across the polar cap region. Analysis of the Swarm in situ plasma measurements revealed that, during the storm’s main phase, all events with extremely enhanced plasma densities (>106 el/cm3) in the polar cap were observed in the Southern Hemisphere. When Swarm satellites crossed these enhancements, degradation of GPS performance was observed, with a sudden decrease in the number of GPS satellites tracked. Our findings indicate that polar patches and TOI structures in the topside ionosphere were predominantly observed in the Southern Hemisphere, which had much higher plasma densities than the Northern Hemisphere, where SED/TOI structures have already been reported earlier. LEO–GPS data (ROTI and topside TEC) were consistent with these results.

Bistatic Sounding of High-Latitude Ionospheric Irregularities Using a Decameter EKB Radar and an UTR-2 Radio Telescope: First Results

We present the first results of the joint Russian–Ukrainian experiments for recording of signals from the EKB radar of the Institute of Solar–Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (Arti observatory of the Institute of Geophysics of the Ural Branch of the Russian Academy of Sciences, Sverdlovsk region, Russia) at a distance of over 1600 km by using a coherent receiving system and a high-gain phased array of the UTR-2 radio telescope (S.Ya. Braude Radioastronomical Observatory (RAO) of the Institute of Radio Astronomy of the Ukrainian National Academy of Sciences (IRA UNAS), Kharkov region, Ukraine). It is shown that two pulse sequences that are identical to the transmitted EKB radar signal, but arrive with different delays were observed at the reception point. The sequence which was received first corresponded to the direct-signal propagation along the great-circle arc. The second sequence was received with delays corresponding to a path length of 2800 to 3400 km and was the result of scattering of the transmitted radar signal by high-latitude ionospheric irregularities. The Doppler frequency shift of the scattered signal was range-dependent and varied from −3 to +4 Hz, which corresponded to the radial component of the ionospheric irregularity velocity from −43 to +58 m/s. To interpret the results of the experiments, we numerically simulated the signal propagation based on the actual ionospheric conditions at an appropriate time. Ionospheric characteristics were retrieved by the vertical ionospheric sounding technique, with the ionosonde located in close proximity to the EKB radar. Comparison between monostatic radar diagnostic results and bistatic sounding results has shown a good agreement of the retrieved parameters of the high-latitude ionospheric irregularities.

Dependence of the high-latitude plasma irregularities on the auroral activity indices: a case study of 17 March 2015 geomagnetic storm

The magnetosphere substorm plays a crucial role in the solar wind energy dissipation into the ionosphere. We report on the intensity of the high-latitude ionospheric irregularities during one of the largest storms of the current solar cycle—the St. Patrick’s Day storm of 17 March 2015. The database of more than 2500 ground-based Global Positioning System (GPS) receivers was used to estimate the irregularities occurrence and dynamics over the auroral region of the Northern Hemisphere. We analyze the dependence of the GPS-detected ionospheric irregularities on the auroral activity. The development and intensity of the high-latitude irregularities during this geomagnetic storm reveal a high correlation with the auroral hemispheric power and auroral electrojet indices (0.84 and 0.79, respectively). Besides the ionospheric irregularities caused by particle precipitation inside the polar cap region, evidences of other irregularities related to the storm enhanced density (SED), formed at mid-latitudes and its further transportation in the form of tongue of ionization (TOI) towards and across the polar cap, are presented. We highlight the importance accounting contribution of ionospheric irregularities not directly related with particle precipitation in overall irregularities distribution and intensity.

Observation of the ionospheric irregularities over the Northern Hemisphere: Methodology and service

Observation and analysis of the ionospheric irregularities at the high latitudes using GPS measurements represent very actual task for both scientific point of view and Global Navigation Satellite Systems (GNSS) applications, as the occurrence of the ionospheric irregularities can impact a variety of communication and navigation systems. In this paper we describe methodology and service for continuous generation of high-resolution maps of the ionospheric irregularities. To observe the high-latitude ionospheric irregularities, data collected from three ground-based GPS networks of the Northern Hemisphere are processed and analyzed. Here we used parameters ROT (rate of total electron content (TEC) change) and ROTI (index of ROT) to study the occurrence of TEC fluctuations Pi et al. (1997). ROTI maps are constructed with the grid of 2° × 2° resolution as a function of the magnetic local time and corrected magnetic latitude. The ROTI maps allow to estimate the overall fluctuation activity and auroral oval evolutions, in general, the ROTI values are corresponded to the probability of the GPS signals phase fluctuations. We demonstrate that the occurrence and magnitude of TEC fluctuations, measured using GNSS networks, increase dramatically during space weather events. The irregularities oval expands considerably equatorward with simultaneous increase of the fluctuation intensity.

An interhemispheric comparison of GPS phase scintillation with auroral emission observed at the South Pole and from the DMSP satellite

<p>The global positioning system (GPS) phase scintillation caused by high-latitude ionospheric irregularities during an intense high-speed stream (HSS) of the solar wind from April 29 to May 5, 2011, was observed using arrays of GPS ionospheric scintillation and total electron content monitors in the Arctic and Antarctica. The one-minute phase-scintillation index derived from the data sampled at 50 Hz was complemented by a proxy index (delta phase rate) obtained from 1-Hz GPS data. The scintillation occurrence coincided with the aurora borealis and aurora australis observed by an all-sky imager at the South Pole, and by special sensor ultraviolet scanning imagers on board satellites of the Defense Meteorological Satellites Program. The South Pole (SP) station is approximately conjugate with two Canadian High Arctic Ionospheric Network stations on Baffin Island, Canada, which provided the opportunity to study magnetic conjugacy of scintillation with support of riometers and magnetometers. The GPS ionospheric pierce points were mapped at their actual or conjugate locations, along with the auroral emission over the South Pole, assuming an altitude of 120 km. As the aurora brightened and/or drifted across the field of view of the all-sky imager, sequences of scintillation events were observed that indicated conjugate auroras as a locator of simultaneous or delayed bipolar scintillation events. In spite of the greater scintillation intensity in the auroral oval, where phase scintillation sometimes exceeded 1 radian during the auroral break-up and substorms, the percentage occurrence of moderate scintillation was highest in the cusp. Interhemispheric comparisons of bipolar scintillation maps show that the scintillation occurrence is significantly higher in the southern cusp and polar cap.</p>

Initial GPS scintillation results from CASES receiver at South Pole, Antarctica

Connected Autonomous Space Environment Sensor (CASES) Global Positioning System (GPS) software‐defined receivers developed for ionospheric scintillation studies have been deployed on Autonomous Adaptive Low‐Power Instrument Platforms (AAL‐PIP) at South Pole, Antarctica. In this paper, we describe the AAL‐PIP experimental setup focusing on CASES. We explain in detail the method developed for analyzing CASES data, and report initial AAL‐PIP CASES results. Furthermore, we compare the CASES measurements with those from a modified Novatel GSV4004 GPS Ionospheric Scintillations and TEC Monitor (GISTM) receiver at the South Pole. CASES receivers have been successfully deployed and reliably operated in equatorial and midlatitude regions. Four of these GPS receivers, for the first time, are deployed in high‐latitude regions as a part of the National Science Foundation (NSF) funded project of deploying space science instrument platforms, AAL‐PIPs, in Antarctica since December 2010–2011. We present initial scintillation results recorded by a CASES receiver at South Pole during the storm on 24 January 2012 along with AAL‐PIP magnetometer observations. We have deduced that the CASES receiver scintillation observations agree with those from the Novatel GPS scintillation receiver. Since this is the first time a CASES receiver has been deployed to operate in a high latitude, low temperature, and low humidity environment, we consider this comparison a demonstration of its reliable operation as a science‐grade scintillation receiver in such conditions. We plan to study high latitude ionospheric irregularities by using observations from CASES and other ancillary instruments from Antarctica coupled with physical parameters derived from models.

Comparison of boundaries for HF auroral backscatter and VHF scintillation

A study is described of the equatorwards boundary of high-latitude ionospheric irregularities using measurements obtained by two different experimental techniques. Auroral traces observed on backscatter ionograms from an HF radar have been used to identify the boundary of the decametre scale-size irregularities responsible for the coherent backscatter. Simultaneous observations of scintillation on the 150 MHz signals from NNSS satellites have enabled the boundary for irregularities in the sub-kilometre scale regime to be located. Comparisons of the results from the two techniques indicate that reconciliation between boundary positions can be made in only about 50% of the cases considered. In general the scintillation boundary lies on average well polewards of that identified by the HF radar, suggesting that caution should be exercised in the mapping of irregularity boundary positions.