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Irk Shagimuratov

Bio: Irk Shagimuratov is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: TEC & Total electron content. The author has an hindex of 20, co-authored 66 publications receiving 956 citations.


Papers
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Journal ArticleDOI
TL;DR: In this article, the properties of the ionospheric electron density profiles retrieved from COSMIC radio occultation measurements were compared with ground-based measurements, and it was shown that COS MIC profiles are usually in good agreement with ionosonde profiles, both in the F2 layer peak electron density and the bottom side of the profiles.
Abstract: This research is motivated by the recent IGS Ionosphere Working Group recommendation issued at the IGS 2010 Workshop held in Newcastle, UK. This recommendation encourages studies on the evaluation of the application of COSMIC radio occultation profiles for additional IGS global ionosphere map (GIM) validation. This is because the reliability of GIMs is crucial to many geodetic applications. On the other hand, radio occultation using GPS signals has been proven to be a promising technique to retrieve accurate profiles of the ionospheric electron density with high vertical resolution on a global scale. However, systematic validation work is still needed before using this powerful technique for sounding the ionosphere on a routine basis. In this paper, we analyze the properties of the ionospheric electron density profiling retrieved from COSMIC radio occultation measurements. A comparison of radio occultation data with ground-based measurements indicates that COSMIC profiles are usually in good agreement with ionosonde profiles, both in the F2 layer peak electron density and the bottom side of the profiles. For this comparison, ionograms recorded by European ionospheric stations (DIAS network) in 2008 were used.

93 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the features of pre-earthquake ionospheric anomalies in the total electron content (TEC) data obtained on the basis of regular GPS observations from the International GNSS Service (IGS) network.

71 citations

Journal ArticleDOI
TL;DR: The analysis of the ionospheric total electron content (TEC) variations obtained with using GPS measurements before the Hokkaido earthquake (M = 8.3) is presented in this paper.
Abstract: In this paper the analysis of the ionospheric total electron content (TEC) variations obtained with using GPS measurements before the Hokkaido earthquake (M = 8.3) is presented. Anomalous behavior of TEC was detected within several days before the main event. Anomaly appeared as the local TEC enhancement situated in the vicinity of the forthcoming earthquake epicenter. These structures occurred during 5 days prior to the shock at the same interval of local time. At the process of the earthquake approach the amplitude of modification was increased, and it has reached the 85–90% level relative to the non-disturbed conditions 18 hours before the earthquake. The area of strong positive disturbance has extended over 1500 km in latitudes and 4000 km in longitudes. The analysis have shown that according to the series of characteristics (its locality, affinity with the epicenter, dome-shaped zone of manifestation, characteristic time of existence) the detected ionospheric anomaly may be associated to the precursors of seismic activity.

60 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the features of pre-earthquake ionospheric anomalies in the total electron content (TEC) data obtained on the basis of regular GPS observations from the IGS network.
Abstract: . This paper investigates the features of pre-earthquake ionospheric anomalies in the total electron content (TEC) data obtained on the basis of regular GPS observations from the IGS network. For the analysis of the ionospheric effects of the 26 December 2004 Indonesian earthquake, global TEC maps were used. The possible influence of the earthquake preparation processes on the main low-latitude ionosphere peculiarity – the equatorial anomaly – is discussed. Analysis of the TEC maps has shown that modification of the equatorial anomaly occurred a few days before the earthquake. For 2 days prior to the event, a positive effect was observed in the daytime amplification of the equatorial anomaly. Maximal enhancement in the crests reached 20 TECU (50–60%) relative to the non-disturbed state. In previous days, during the evening and night hours (local time), a specific transformation of the TEC distribution had taken place. This modification took the shape of a double-crest structure with a trough near the epicenter, though usually in this time the restored normal latitudinal distribution with a maximum near the magnetic equator is observed. It is assumed that anomalous electric field generated in the earthquake preparation zone could cause a near-natural "fountain-effect" phenomenon and might be a possible cause of the observed ionospheric anomaly.

58 citations

Journal ArticleDOI
TL;DR: In this article, the authors compared IRI-2012 and IRI Plas models with diurnal GPS vTEC data derived from European mid-latitude GPS station Potsdam and found that all models do not represent correctly the topside profile part and tend to overestimate the electron density higher than F2 peak.

53 citations


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Journal ArticleDOI
28 Jan 1983-Science
TL;DR: Specialized experiments with atmosphere and coupled models show that the main damping mechanism for sea ice region surface temperature is reduced upward heat flux through the adjacent ice-free oceans resulting in reduced atmospheric heat transport into the region.
Abstract: The potential for sea ice-albedo feedback to give rise to nonlinear climate change in the Arctic Ocean – defined as a nonlinear relationship between polar and global temperature change or, equivalently, a time-varying polar amplification – is explored in IPCC AR4 climate models. Five models supplying SRES A1B ensembles for the 21 st century are examined and very linear relationships are found between polar and global temperatures (indicating linear Arctic Ocean climate change), and between polar temperature and albedo (the potential source of nonlinearity). Two of the climate models have Arctic Ocean simulations that become annually sea ice-free under the stronger CO 2 increase to quadrupling forcing. Both of these runs show increases in polar amplification at polar temperatures above-5 o C and one exhibits heat budget changes that are consistent with the small ice cap instability of simple energy balance models. Both models show linear warming up to a polar temperature of-5 o C, well above the disappearance of their September ice covers at about-9 o C. Below-5 o C, surface albedo decreases smoothly as reductions move, progressively, to earlier parts of the sunlit period. Atmospheric heat transport exerts a strong cooling effect during the transition to annually ice-free conditions. Specialized experiments with atmosphere and coupled models show that the main damping mechanism for sea ice region surface temperature is reduced upward heat flux through the adjacent ice-free oceans resulting in reduced atmospheric heat transport into the region.

1,356 citations

Journal ArticleDOI
TL;DR: The results indicate that GPS and GLONASS intra-frequency biases obtained in this work show the same precision levels as those estimated by DLR (about 0.1 and 0.4 ns for the two constellations, respectively, with respect to the products of CODE).
Abstract: In order to better understand the differential code biases (DCBs) of global navigation satellite system, the IGGDCB method is extended to estimate the intra- and inter-frequency biases of the global positioning system (GPS), GLONASS, BeiDou navigation satellite system (BDS), and Galileo based on observations collected by the multi-GNSS experiment (MGEX) of the international GNSS service (IGS). In the approach of IGGDCB, the local ionospheric total electronic content is modeled with generalized triangular series (GTS) function rather than using a global ionosphere model or a priori ionospheric information. The DCB estimated by the IGGDCB method is compared with the DCB products from the Center for Orbit Determination in Europe (CODE) and German Aerospace Center (DLR), as well as the broadcast timing group delay (TGD) parameters over a 2-year span (2013 and 2014). The results indicate that GPS and GLONASS intra-frequency biases obtained in this work show the same precision levels as those estimated by DLR (about 0.1 and 0.2–0.4 ns for the two constellations, respectively, with respect to the products of CODE). The precision levels of IGGDCB-based inter-frequency biases estimated over the 24-month period are about 0.29 ns for GPS, 0.56 ns for GLONASS, 0.36 ns for BDS, and 0.24 ns for Galileo, respectively. Here, the accuracies of GPS and GLONASS biases are assessed relative to the products of CODE, while those of BDS and Galileo are compared with the estimates of DLR. In addition, the monthly stability indices of IGGDCB-based DCBs are 0.11 (GPS), 0.18 (GLONASS), 0.17 (BDS), and 0.14 (Galileo) ns for the individual constellation.

268 citations

28 Nov 2002
TL;DR: In this paper, a method to derive the ionospheric total electron content (TEC) and to estimate the biases of GPS satellites and dual frequency receivers using the GPS Earth Observation Network (GEONET) in Japan is presented.
Abstract: Abstract. This paper presents a method to derive the ionospheric total electron content (TEC) and to estimate the biases of GPS satellites and dual frequency receivers using the GPS Earth Observation Network (GEONET) in Japan. Based on the consideration that the TEC is uniform in a small area, the method divides the ionosphere over Japan into 32 meshes. The size of each mesh is 2° by 2° in latitude and longitude, respectively. By assuming that the TEC is identical at any point within a given mesh and the biases do not vary within a day, the method arranges unknown TECs and biases with dual GPS data from about 209 receivers in a day unit into a set of equations. Then the TECs and the biases of satellites and receivers were determined by using the least-squares fitting technique. The performance of the method is examined by applying it to geomagnetically quiet days in various seasons, and then comparing the GPS-derived TEC with ionospheric critical frequencies (foF2). It is found that the biases of GPS satellites and most receivers are very stable. The diurnal and seasonal variation in TEC and foF2 shows a high degree of conformity. The method using a highly dense receiver network like GEONET is not always applicable in other areas. Thus, the paper also proposes a simpler and faster method to estimate a single receiver’s bias by using the satellite biases determined from GEONET. The accuracy of the simple method is examined by comparing the receiver biases determined by the two methods. Larger deviation from GEONET derived bias tends to be found in the receivers at lower ( Key words. Ionosphere (mid-latitude ionosphere; instruments and techniques) – Radio science (radio-wave propagation)

229 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that most crustal rocks contain dormant electronic charge carriers in the form of peroxy defects, O 3 Si / OO ⧹ SiO 3, known as positive holes.

223 citations

Journal ArticleDOI
TL;DR: In this paper, the maximum ionospheric electron density at F2 peak (NmF2) recorded an unusual large enhancement during the afternoon-sunset sector by the Chinese ionosondes over Wuhan (30.5°N, 114.4°E) and Xiamen (24.9°E), which are close to the earthquake epicenter.
Abstract: [1] On 12 May 2008 at 0628 UT a major earthquake Ms = 8.0 struck Wenchuan County (31.0°N, 103.4°E) in southwest China. The maximum ionospheric electron density at F2 peak (NmF2) recorded an unusual large enhancement during the afternoon-sunset sector by the Chinese ionosondes over Wuhan (30.5°N, 114.4°E) and Xiamen (24.4°N, 123.9°E), which are close to the earthquake epicenter. An averaged increase at these two stations is about 2 times on a geomagnetic quiet day, 9 May (Kp ≤ 2), 3 days prior to the earthquake, relative to the median value of 1–12 May, whereas the increase was much less significant over Yamagawa (31.2°N, 130.6°E) and Okinawa (26.7°N, 128.2°E) in Japan. Combining the data from the network of 58 global positioning system receivers around China and the global ionospheric map, the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90°–130°E. Our results suggest that this abnormal enhancement is most possibly a seismo-ionospheric signature.

201 citations