Irk Shagimuratov

The response of the ionospheric total electron content to the solar eclipse on August 11, 1999

Abstract The GPS observations from EUREF permanent GPS network were used to observe the response of TEC (Total Electron Content) to the total solar eclipse under quiet geomagnetic conditions of the daytime ionosphere. The effect of the eclipse was detected in diurnal variations and more distinctly in the variations of TEC along individual satellite passes. The trough-like variations with a gradual decrease and followed by increase of TEC at the time of the eclipse were observed at all European stations. Depression of TEC amounted to 2–8 TECU. The delay of a minimum level of TEC with respect to the maximum phase of eclipse was 10–20 min. The effect of the eclipse was also detected at distance over 1500 km to the north from path of the eclipse. The high-resolution TEC maps produced with 15 minute intervals demonstrate the essential change in the structure of the ionosphere during the eclipse.

Physical interpretation and mathematical simulation of ionospheric precursors of earthquakes at midlatitudes

The paper presents the results of studying anomalous variations in the total electron content (TEC) of the ionosphere as probable precursors of strong seismic events. The vertical drift of the F2 layer’s ionospheric plasma under the effect of seismically generated zonal electric field is considered as a likely reason for the observed variations in the TEC. An estimation of this drift effects is made by mathematical simulation utilizing the global numerical model of the Earth’s upper atmosphere (UAM). Midlatitude ionospheric effects were simulated. Two types of seismogenerated electric fields (dipole and monopole) were used with various magnitudes and spatial configurations. The derived results were compared with the TEC data of GPS observations from the IGS for the Kitira earthquake in southern Greece (January 8, 2006; M 6.8). It was shown that variations generated by additional sources of the dipole type are consistent with the observed data; monopole-type sources did not reproduce some typical peculiarities of these observations and systematically underestimated the deviation value.

Comparison of total electron content obtained from GPS with IRI

Abstract The comparison of the IRI model with TEC estimated using the continuous GPS observations of European part of IGS network is considered. The variability of a measured TEC was analyzed for the low solar activity in the period 1996–1997. We used IRI 90 version with upped height limit 2000 km and IRI 95 up to 1000 km. It is shown that the difference between model and measured TEC depends on latitude and season. Generally, IRI 95 underestimate and IRI 90 overestimate the TEC relative to GPS measurements. The relative difference may reach over 50%.

Observation of the ionospheric storm of October 11, 2008 using FORMOSAT-3/COSMIC data

The electron density profiles retrieved from the COSMIC radio occultation measurements were examined in order to estimate the possibility of its use as additional data source to study changes in electron density distribution occurred during ionospheric storms. The ionosphere behaviour during moderate geomagnetic storm which occurred on October 11, 2008 was analysed. The short-duration positive effect was revealed distinctly in GPS TEC and ionosonde measurements. For the European mid-latitude region it reached the factor of 2 or more relative to the undisturbed conditions. COSMIC data were analyzed and their validity was tested by comparison with ground-based measurements. It was shown the good agreement between independent measurements both in quiet and disturbed conditions. Analysis of COSMIC-derived electron density profiles revealed changes of the bottom-side and topside parts of the ionosphere.

High latitude TEC fluctuations and irregularity oval during geomagnetic storms

GPS measurements obtained by the global IGS network were used to study the occurrence of TEC fluctuations in the northern and southern high-latitude ionosphere during severe geomagnetic storms. In the northern hemisphere, GPS stations located higher than 55N Corrected Geomagnetic Latitude (CGL) at different longitudes were selected. In the southern hemisphere, Antarctic permanent GPS stations were used. Dual-frequency GPS measurements for individual satellite passes served as raw data. As a measure of fluctuation activity the rate of TEC (ROT) was used, and the fluctuation intensity was evaluated using the ROTI index. Using daily GPS measurements from all selected stations, images of the spatial and temporal behavior of TEC fluctuations were formed (in Corrected Geomagnetic Coordinates—CGC and geomagnetic local time—GLT). Similarly to the auroral oval, these images demonstrate an irregularity oval. The occurrence of the irregularity oval relates to the auroral oval, cusp and polar cap. During a storm, the intensity of TEC fluctuations essentially increased. The irregularity oval expands equatorward with an increase of magnetic activity. The study showed that the existing high-latitude GPS stations can provide a permanent monitoring tool for the irregularity oval in near real-time. In this paper, the features of the development of phase fluctuations at the geomagnetic conjugate points, and inter-hemispheric differences and similarities during winter and summer conditions, are discussed.

Ionospheric total electron content behaviour during November 1997 storm

Abstract The GPS observations carried out by IGS stations were used to study TEC changes on global scale during storm on 22 November 1997. We analysed the spatial and temporal TEC changes through time series at selected sites and maps for different sectors of northern hemisphere in comparison with the quiet TEC variations. The positive effect in the behaviour of TEC during the storm was prevailed on global scale at middle latitudes. The strong negative effect was observed at auroral and subauroral latitudes only over America. TEC behaviour on first stage of storm was similar to TEC development of storm on 10 January 1997. The long positive effect is the significant feature in viewed storm, which is probably due to the long duration and complex development of the storm.

Impact Of Tec Fluctuations In The Antarctic Ionosphere On Gps Positioning

Impact Of Tec Fluctuations In The Antarctic Ionosphere On Gps Positioning With increasing reliance on space-based platforms for global navigation and communication, concerns about the impact of ionospheric scintillation and total electron content fluctuations on these systems have became a high priority. In this paper, GPS transionospheric signals have been used to study the development of ionospheric phase fluctuations observed at Antarctic IGS permanent stations: McMurdo-MCM4, Casey-CAS1, Mawson-MAW1, Sanae-VESL, Syowa-SYOG and Davis-DAV1 in 2001. The use of the multi-station, multi-path observations of the GPS beacons has allowed the study of the time development of irregularities as a function of latitude and longitude of individual geomagnetic storms. The basic storms studied were those of March 19-20, March 31, April 9-11, June 16-17, and September 23, 2001. The rate of TEC (ROT) parameter was used to study the occurrence of TEC fluctuations. The results from studying these storms showed the unique nature of each storm. For the above five storms, data were available from three auroral stations (VESL, SYOG and MAW1) and from 61° to 70° Corrected Geomagnetic Latitude (CGL). In addition, data from three higher latitude polar stations (DAV1, MCM4 and CAS1) near 800 CGL are also analysed. Fluctuation effects, causing dramatic changes in total electron content - TEC, can have a different impact on GPS positioning accuracy (especially during phase ambiguity resolution). Bernese ver.4.2 software was used for the analysis of the GPS permanent data from Antarctic IGS stations. The analyses rely on studying the repeatability of vector co-ordinates. These vectors were investigated during the geomagnetic storms when the intensity of TEC fluctuations was more pronounced. The impact of TEC fluctuations in the high latitude ionosphere on GPS positioning accuracy has been discussed in terms of the total number of observations of doubledifferences (DD) and in the ratio of the total number of all ambiguities to unresolved ones.

Use of total electron content maps for analysis of spatial-temporal structures of the ionosphere

The main aspects of a methodology for determining the total electron content (TEC) of the ionosphere from GPS observations and the principles of using two-frequency measurements of satellite signal delays in navigation systems are presented. The method developed and used at the Western Department of Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Waves Propagation, RAS enables to determine the absolute values of the TEC and monitor the diurnal behavior of this quantity for individual monitoring stations. The methodology for obtaining information on the spatial distribution of TEC maps of the ionosphere on the basis of an algorithm for multi-station processing of GPS observations. Using a set of algorithms and programs, regional TEC maps with a spatial resolution of 1° and a time resolution of 15 min-1 h are regularly drawn. This precision allows using TEC maps for studying the structure and dynamics of the ionosphere during different geophysical events. The results of studies of the response of the ionosphere to the solar eclipse on November 3, 2005 and the geomagnetic storms on January 22, 2012.

Use of GLONASS for studying the ionosphere

Results of using the Russian Global Navigation Satellite System (GLONASS) to measure absolute values of the ionosphere’s total electron content (TEC) are presented. Specific features of configurations and differences in parameters of GLONASS and GPS are given, and their impact on TEC evaluation is analyzed. The statistical analysis is also carried out for comparing the TEC measurement data obtained from the GPS and GLONASS observations; a high correlation between measurements of both systems is shown. Investigations have revealed that the use of both systems allows of extending the possibilities of their employment for studying the ionosphere’s structure and dynamics. To restore the diurnal behavior of TEC of the ionosphere above the observation station, the phase measurements are proposed to be taken as input data. Their advantage over the group measurements is not only their high accuracy but the fact that they are less subject to the multipath effect. The technique for processing the phase observations implemented for GLONASS is an essential part of the system for monitoring of the ionosphere over the European part of p]Russia, which is under development at the West Department of Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation.

PRE-EARTHQUAKES, an FP7 project for integrating observations and knowledges on earthquake precursors: Preliminary results and strategy

PRE-EARTHQUAKES (Processing Russian and European EARTH observations for earthQUAKE precursors Studies) EU-FP7 project is devoted to demonstrate - integrating different observational data, comparing and improving different data analysis methods - how it is possible to progressively increase reliability of short term seismic risk assessment. Three main testing area were selected (Italy, Turkey and Sakhalin) in order to concentrate observations and integration efforts starting with a learning phase on selected events in the past devoted to identify the most suitable parameters, observations technologies, data analysis algorithms. For these areas, different ground (80 radon and 29 spring water stations in Turkey region, 2 magneto-telluric in Italy) and satellite (18 different systems) based observations, 11 data analysis methods, for 7 measured parameters, have been compared and integrated. A specific integration platform (PEG, Pre-Earthquakes Geoportal) based on OGC (Open Geospatial Consortium) standards, was developed to operate a products integration, cross-validation and scientific interpretation.