Papers by Tamara Gulyaeva
Geodesy and Geodynamics, 2016
Total Electron Content (TEC) is an important observable parameter of the ionosphere which forms t... more Total Electron Content (TEC) is an important observable parameter of the ionosphere which forms the main source of error for space based navigation and positioning systems. Since the deployment of Global Navigation Satellite Systems (GNSS), cost-effective estimation of TEC between the earth based receiver and Global Positioning System (GPS) satellites became the major means of investigation of local and regional disturbance for earthquake precursor and augmentation system studies. International Reference Ionosphere (IRI) extended to plasmasphere (IRI-Plas) is the most developed ionospheric and plasmaspheric climatic model that provides hourly, monthly median of electron density distribution globally. Recently, IONOLAB group (www.ionolab.org) has presented a new online space weather service that can compute slant TEC (STEC) on a desired ray path for a given date and time using IRI-Plas model (IRI-Plas-STEC). In this study, the performance of the model based STEC is compared with GPS-STEC computed according to the estimation method developed by the IONOLAB group and includes the receiver bias as IONOLAB-BIAS (IONOLAB-STEC). Using Symmetric KullbackeLeibler Distance (SKLD), Cross Correlation (CC) coefficient and the metric norm (L2N) to compare IRI-Plas-STEC and IONOLAB-STEC for the month of October 2011 over the Turkish National Permanent GPS Network (TNPGN-Active), it has been observed that SKLD provides a good indicator of disturbance for both earthquakes and geomagnetic storms.
Acta Geodaetica et Geophysica Hungarica
Systematic difference between observed vertical TEC estimated from GPS-GLONASS observations and m... more Systematic difference between observed vertical TEC estimated from GPS-GLONASS observations and model average TEC provided by SMI-96 ionosphere-plasmasphere model has been found. To make relevant calibration of observed TECo, measured data have been averaged at three regional windows: [55–65°N, 23–37°E], [55–65°N, 83–97°E], and [45–55°N, 128–142°E], resulting in good correlation with SMI-96 TECm model values. The correlation coefficients and mean diurnal values of TECo and TECm are used for calibration of TECo until a reasonable consistency of vertical TECo with TECm is reached. The model-based algorithm preserves day-to-day TEC variability and provides monthly-mean data for model improvement.
41st COSPAR Scientific Assembly, Jul 1, 2016
Recommendations from the Chapman Conference on Scientific Challenges Pertaining to Space Weather ... more Recommendations from the Chapman Conference on Scientific Challenges Pertaining to Space Weather Forecasting Including Extremes, 11-15 February 2019, Pasadena, CA, USA. Endorsers of this report are listed as Other below the author list. For meeting artifacts, see https://doi.org/10.5281/zenodo.3693004. The meeting was sponsored by NSF Award AGS 1848885 and by NASA grants 936723.02.01.09.14 and 936723.02.01.11.21.
Earth, Planets and Space, 2009
The F2 layer peak plasma density N m F 2 is reduced by the factor constructed from the relative c... more The F2 layer peak plasma density N m F 2 is reduced by the factor constructed from the relative changes in the Sun’s zenith angle ξ for a particular local time and the local noon value χ0. Proposed transformation yields a proxy for the peak plasma density which coincides with the source observation at noon but apart from the latter is gradually reduced towards the night. Hourly observations at 8 ground based ionosondes for the solar maximum (2000) and minimum (2006) are analyzed for inter-stations and inter-seasonal correlation of the peak plasma density and the proxy values. The proxy values show improved correlation between the data at different locations and improved inter-seasonal correlations for a particular location due to greater homogeneity of results throughout the year contributing to improved evaluation of the ionospheric weather indices.
Journal of Geography, Environment and Earth Science International, 2016
Regions of the permanent ionosphere instability are identified with 24h daily global W-index maps... more Regions of the permanent ionosphere instability are identified with 24h daily global W-index maps produced from Global Ionospheric Maps of Total Electron Content, GIM-TEC, provided by Jet Propulsion Laboratory. Planetary Wp index derived from hourly W-index maps from January, 1999, to present, is used to compile Catalogue of more than 270 ionospheric storms which comprise 8% of total database, and the rest represents quiet conditions. The positive storm percentage occurrence (enhanced electron density, pW + ) and negative storm occurrence (depleted electron density, pW ) are analyzed in space and time showing dependence on solar activity (SA) and seasons for the global ionosphere and its adopted 240 sub-domains (of latitude bins equal to 10o in the polar regions and 20 ° elsewhere and 15 ° hourly longitude bins). A global occurrence of pW
Annales Geophysicae, 2004
Annales Geophysicae, 2008
Advances in Space Research, 2011
The International Reference Ionosphere model extended to the plasmasphere, IRI-Plas, presents glo... more The International Reference Ionosphere model extended to the plasmasphere, IRI-Plas, presents global electron density profiles and total electron content, TECiri, up to the altitude of the GPS satellites (20,000 km). The model code is modified by input of GPS-derived total electron content, TECgps, so that the topside scale height, Hsc, is obtained minimizing in one step the difference between TECiri and TECgps observation. The topside basis scale height, Hsc, presents the distance in km above the peak height at which the peak plasma density, NmF2, decays by a factor of e ($2.718). The ionosonde derived F2 layer peak density and height and GPS-derived TECgps data are used with IRI-Plas code during the main phase of more than 100 space weather storms for a period of 1999-2006. Data of seven stations are used for the analysis, and data from five other stations served as testing database. It is found that the topside basis scale height is growing (depressing) when the peak electron density (critical frequency foF2) and electron content are decreased (increased) compared to the median value, and vice versa. Relative variability of the scale height, rHsc, and the instantaneous Hsc are inferred analytically in a function of the instantaneous foF2, median fmF2 and median Hmsc avoiding a reference to geomagnetic indices. Results of validation suggest reliability of proposed algorithm for implementation in an operational mode.
Advances in Space Research, 1997
Advances in Space Research, 1995
Two factors affecting the ionosphere disturbances are considered. First — the solar corona and th... more Two factors affecting the ionosphere disturbances are considered. First — the solar corona and the heliospheric current sheet orientation with respect to the Earth during the sunspot cycle. Second — twilight conditions at different latitudinal zones. Formulae for determining day of edgewise orientation of the solar corona towards the Earth are derived. It is shown that enhanced disturbances in the auroral electrojet occur when the IMF polarity deduced from geomagnetic data has the least departures from parameter of orientation of the solar corona and the HCS. Days of edgewise turned dipole magnetic equator of the Sun are given for the declining phase of the current solar cycle. At mid-latitudes the negative ionosphere disturbances are enhanced at equinoxes while positive disturbances are greater at winter, both types are prevailing at night and dawn. The ionospheric disturbance is minimum during the solar maximum at mid-latitudes but this effect is vanishing towards the geomagnetic equator.
Advances in Space Research, 2007
Comparisons of two model results with Global Positioning System, GPS-TEC, measurements have been ... more Comparisons of two model results with Global Positioning System, GPS-TEC, measurements have been carried out for different latitudinal, solar activity, magnetic activity, diurnal, and seasonal conditions. The models evaluated are the Global Core Plasma Model (GCPM-2000) and the IRI extension (IRI*) with the Russian plasmasphere model. Data from 23 observatories providing GPS-TEC and ionosonde data have been used. It is shown that the IRI* plasmasphere electron densities are greater than the GCPM results by an order of magnitude at 6370 km altitude (one Earth radius), becoming two to three orders of magnitude larger at the GPS satellite orbital altitude of 20,200 km. Another source of model and GPS-TEC differences is the selection of the ionospheric F2 layer peak parameters driving the models, either with ITU-R (former CCIR) maps or ionosonde observations. The plasmasphere model extension of IRI improves the accuracy of the TEC model predictions taking into account the plasmasphere contribution to the total electron content which could vary from 10% during daytime under quiet magnetic conditions to more than 50% during the night under storm-time conditions.
Advances in Space Research, 2001
Advances in Space Research, 1990
Abstract Neglect of ionisation in the E-F valley region causes appreciable errors in the F-region... more Abstract Neglect of ionisation in the E-F valley region causes appreciable errors in the F-region heights calculated from ionograms. In order to minimize such errors, one-component analysis methods use heuristic relations, e.g. between the real and virtual height of a ‘key point’ above the valley. A considerable reduction of the errors is obtained by a combined analysis of o- and x- data. The analysis can determine only one parameter, reflecting basically the valley width, so some model must be used for the shape and depth of the valley. When the real ionosphere deviates from the ideal model, ionospheric irregularities give different variations in the o- and x- components. Such contradictory information cannot be combined in a joint solution. Increased technical accuracy cannot ‘circumnavigate’ this difficulty. Thus for further progress we must use carefully calibrated rocket and backscatter data to obtain reliable, median models for valley size and depth under different conditions.
Advances in Space Research, 2010
Accuracy of IRI electron density profile depends on the F2 layer peak density and height converte... more Accuracy of IRI electron density profile depends on the F2 layer peak density and height converted by empirical formulae from the critical frequency and M3000F2 factor provided by the ITU-R (former CCIR). The CCIR/ITU-R maps generated from ground-based ionosonde measurements suffer from model assumptions, in particular, over the oceans where relatively few measurements are available due to a scarcity of ground-based ionosondes. In the present study a grid-point calibration of IRI/ITU-R maps for the foF2 and hmF2 over the oceans is proposed using modeling results based on the topside true-height profiles provided by ISIS1, ISIS2, IK-19 and Cosmos-1809 satellites for the period of 1969-1987. Topside soundings results are compared with IRI and the Russian standard model of ionosphere, SMI, and grouped to provide an empirical calibration coefficient to the peak density and height generated from ITU-R maps. The grid-point calibration coefficients maps are produced in terms of the solar activity, geodetic latitude and longitude, universal time and season allowing update of IRI-ITU-R predictions of the F2 layer peak parameters.
Advances in Space Research, 1998
Acta Geodaetica et Geophysica Hungarica, 2002
ABSTRACT
Solnechno-Zemnaya Fizika, 2016
The International Reference Ionosphere (IRI) imports global effective ionospheric IG12 index base... more The International Reference Ionosphere (IRI) imports global effective ionospheric IG12 index based on ionosonde measurements of the critical frequency foF2 as a proxy of solar activity. Similarly, the global electron content (GEC), smoothed by the sliding 12-months window (GEC12), is used as a solar proxy in the ionospheric and plasmaspheric model IRI-Plas. GEC has been calculated from global ionospheric maps of total electron content (TEC) since 1998 whereas its productions for the preceding years and predictions for the future are made with the empirical model of the linear dependence of GEC on solar activity. At present there is a need to re-evaluate solar and ionospheric indices in the ionospheric models due to the recent revision of sunspot number (SSN2) time series, which has been conducted since 1st July, 2015 [Clette et al., 2014]. Implementation of SSN2 instead of the former SSN1 series with the ionospheric model could increase model prediction errors. A formula is proposed...
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Papers by Tamara Gulyaeva