IRI-Plas Model Research Articles

Model based Computerized Ionospheric Tomography in space and time

Reconstruction of the ionospheric electron density distribution in space and time not only provide basis for better understanding the physical nature of the ionosphere, but also provide improvements in various applications including HF communication. Recently developed IONOLAB-CIT technique provides physically admissible 3D model of the ionosphere by using both Slant Total Electron Content (STEC) measurements obtained from a GPS satellite - receiver network and IRI-Plas model. IONOLAB-CIT technique optimizes IRI-Plas model parameters in the region of interest such that the synthetic STEC computations obtained from the IRI-Plas model are in accordance with the actual STEC measurements. In this work, the IONOLAB-CIT technique is extended to provide reconstructions both in space and time. This extension exploits the temporal continuity of the ionosphere to provide more reliable reconstructions with a reduced computational load. The proposed 4D-IONOLAB-CIT technique is validated on real measurement data obtained from TNPGN-Active GPS receiver network in Turkey.

NeQuick 2 and IRI Plas VTEC predictions for low latitude and South American sector

Using vertical total electron content (VTEC) measurements obtained from GPS satellite signals the capability of the NeQuick 2 and IRI Plas models to predict VTEC over the low latitude and South American sector is analyzed. In the present work both models were used to calculate VTEC up to the height of GPS satellites. Also, comparisons between the performance of IRI Plas and IRI 2007 have been done. The data correspond to June solstice and September equinox 1999 (high solar activity) and they were obtained at nine stations. The considered latitude range extends from 18.4°N to −64.7°N and the longitude ranges from 281.3°E to 295.9°E in the South American sector. The greatest discrepancies among model predictions and the measured VTEC are obtained at low latitudes stations placed in the equatorial anomaly region. Underestimations as strong as 40 TECU [1 TECU = 1016 m−2] can be observed at BOGT station for September equinox, when NeQuick2 model is used. The obtained results also show that: (a) for June solstice, in general the performance of IRI Plas for low latitude stations is better than that of NeQuick2 and, vice versa, for highest latitudes the performance of NeQuick2 is better than that of IRI Plas. For the stations TUCU and SANT both models have good performance; (b) for September equinox the performances of the models do not follow a clearly defined pattern as in the other season. However, it can be seen that for the region placed between the Northern peak and the valley of the equatorial anomaly, in general, the performance of IRI Plas is better than that of NeQuick2 for hours of maximum ionization. From TUCU to the South, the best TEC predictions are given by NeQuick2.The source of the observed deviations of the models has been explored in terms of CCIR foF2 determination in the available ionosonde stations in the region. Discrepancies can be also related to an unrealistic shape of the vertical electron density profile and or an erroneous prediction of the plasmaspheric contribution to the vertical total electron content. Moreover, the results of this study could be suggesting that in the case of NeQuick, the underestimation trend could be due to the lack of a proper plasmaspheric model in its topside representation. In contrast, the plasmaspheric model included in IRI, leads to clear overestimations of GPS derived TEC.

Comparison of IRI_PLAS and IRI_2012 Model Predictions with GPS-TEC Measurements in Different Latitude Regions

The International Reference Ionosphere (IRI) is an empirical model for providing ionospheric parameters, including Total Electron Content (TEC), electron density, electron and ion temperature etc., in the altitude range from 50 km to 2000 km. Since the IRI model is limited up to 2000 km, IRI-PLAS model, plasmasphere extension of the IRI model, was proposed by the researchers. This paper investigates the TEC prediction performance of IRI-PLAS and IRI-2012 models by comparing GPS TEC data, in different latitude regions for magnetically active and quiet days. TEC data over 9 International GNSS Service (IGS) stations, located in different latitude regions, are used for the comparison. Evaluation of the diurnal results reveals good agreement with correlation coefficient >0.9 between GPS-TEC and empirical models for the quiet day irrespectively of the latitudinal data used. However, while the differences are not relatively high in most part of the active day, they reach high level, above 30 TECu, in some part of the day.

Earthquake aftereffects in the Equatorial Ionization Anomaly region under geomagnetic quiet and storm conditions

In addition to multi-scale spatio-temporal trends that shape the ionosphere variability, the ionosphere responds to the disturbances that are solar, geomagnetic and seismic in origin. In this study, post-seismic ionospheric disturbances are investigated retrospectively from 1999 to 2015 using two different sets of ionospheric maps of the F2 layer critical frequency, foF2. One set of foF2 maps is obtained by assimilating Global Ionospheric Maps (GIM) of Total Electron Content (TEC) into IRI-Plas model (IRI-Plas-foF2). Another set of hourly foF2 maps is obtained using PRIME-251 mapping technique (PRIME-foF2) by the assimilation of ionosonde foF2 data into IRI-CCIR model. The geomagnetic storms affecting the ionosphere are determined with relevant thresholds of geomagnetic AE, aa, ap, ap(τ) and Dst indices. It is observed that more than 60% of the earthquakes occur in the Equatorial Ionization Anomaly (EIA) region within the belt of geomagnetic latitudes ±40° N and geographic longitudes 90–190° E. The co-seismic foF2 disturbances, DfoF2, are identified for the cells of the map if an instant foF2 value is outside of pre-defined bounds of foF2 median (μ) and standard deviation (σ), μ±1σ, in the map fragment of 1000kmradius around the earthquake hypocenter. The results of positive ionospheric disturbances, DfoF2p, and negative disturbances, DfoF2n, in the EIA region during the 12h after earthquake differ with respect to geomagnetic quiet and storm conditions, nighttime and daytime, magnitude and depth of the earthquake. The maximum spatial variability (for more than 50% of map cells in the vicinity of hypocenter) is observed with positive disturbances (DfoF2p) for the earthquakes that occurred during daytime at a depth of 70–300km.

Modification of the solar activity indices in the International Reference Ionosphere IRI and IRI-Plas models due to recent revision of sunspot number time series

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 July 1, 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 to transform the smoothed SSN212 series to the proxy of the former basic SSN112=R12 index, which is used by the IRI and IRI-Plas models for long-term ionospheric predictions. Regression relationships are established between GEC12, the sunspot number R12, and the proxy solar index of 10.7 cm microwave radio flux, F10.712. Comparison of calculations by the IRI-Plas and IRI models with observations and predictions for Moscow during solar cycles 23 and 24 has shown the advantage of implementation of GEC12 index with the IRI-Plas model.

Модификация индексов солнечной активности в международных справочных моделях ионосферы IRI и IRI-Plas в связи с пересмотром ряда чисел солнечных пятен

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 to transform the smoothed SSN212 series to the proxy of the former basic SSN112=R12 index, which is used by IRI and IRI-Plas models for long-term ionospheric predictions. Regression relationships are established between GEC12, the sunspot number R12, and the proxy solar index of 10.7 cm microwave radio flux, F10.712. Comparison of calculations by the IRI-Plas and IRI models with observations and predictions for Moscow during solar cycles 23 and 24 has shown the advantage of implementation of GEC12 index with the IRI-Plas model.

Performance of GPS slant total electron content and IRI-Plas-STEC for days with ionospheric disturbance

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 Kullback–Leibler 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.

Comparative analysis of two new empirical models IRI-Plas and NGM (the Neustrelitz Global Model)

Empirical ionospheric models are under continuous development and the new model versions need to be tested and validated. In this paper two new models, the International Reference Ionosphere-Plasmasphere (IRI-Plas) and the Neustrelitz Global Model (NGM) are compared to the standard International Reference Ionosphere (IRI) in different geographical areas. Comparison is fulfilled separately for foF2, ТЕС, the equivalent slab thickness τ. In a middle-latitude area, the foF2(NGM) model has not improved results of foF2(IRI). For subauroral areas, conditions have appeared at which foF2(NGM) provides comparable or better results than foF2(IRI). In low-latitude and equatorial areas, there are conditions when foF2(NGM) is closer to experimental data than foF2(IRI). In middle- and high-latitude areas, TEC(NGM) and TEC(IRI-Plas) provide better results, than TEC(IRI). The IRI-Plas model is better than NGM except for winter months. In low-latitude and equatorial areas, the ТЕС(NGM) model has shown essential advantages. The parameter τ(NGM) provides in most cases the better conformity of the calculated foF2 with observational ones than τ(IRI) and τ(IRI-Plas).

Vertical TEC representation by IRI 2012 and IRI Plas models for European midlatitudes

Vertical total electron content (vTEC) values computed using IRI-2012 and IRI Plas models have been compared with diurnal GPS vTEC data derived from European mid-latitude GPS station Potsdam. Comparative data-model analysis does not reveal good performance in vTEC representation. It was found that new extension of IRI model – IRI Plas – cannot represent correctly the vTEC variations over European midlatitudes and mainly overestimates GPS vTEC especially for low and moderate solar activity. In order to estimate the source of the data-model discrepancies, the case-study with detailed analysis of the model simulated electron density profiles was done. It was obtained that all models do not represent correctly the topside profile part and tend to overestimate the electron density higher than F2 peak. So, the main problem of the IRI vTEC representation is not situated in the plasmaspheric part, its absence in IRI model or its presence in IRI Plas model, the main source of the resulted discrepancies is still in the IRI topside ionosphere representation.

Estimation of $hmF2$ and $foF2$ Communication Parameters of Ionosphere $F2$-Layer Using GPS Data and IRI-Plas Model

F2-layer is the most important and characteristic layer of the ionosphere in the propagation of high frequency (HF) waves due to the highest level of conductivity in the propagation path. In this study, the relation of Total Electron Content (TEC) with the maximum ionization height (hmF2) and the critical frequency (foF2) of F2-layer are investigated within their defined parametric range using the IRI model extended towards the plasmasphere (IRI-Plas). These two parameters are optimized using daily observed GPS-TEC (IONOLAB-TEC) in an iterational loop through Non-Linear Least Squares (NLSQ) optimization while keeping the physical correlation between hmF2 and foF2 parameters. Optimization performance is examined for daily (24-hour) and hourly TEC optimizations separately. It is observed that hourly TEC optimization produces results with much smaller estimation errors. As a result of the hourly optimization, we obtain the hourly hmF2 and foF2 estimates as they are the optimization parameters. Obtained hmF2 and foF2 estimates are compared with the ionosonde estimates for various low, middle and high latitude locations for both quite and disturbed days of ionosphere. The results show that hmF2 and foF2 estimates obtained from IRI-Plas optimization (IRI-Plas-Opt) and ionosonde are very much in agreement with each other. These results also signify that IRI-Plas provides a reliable background model for ionosphere. With the proposed method, it is possible to build a virtual ionosonde via optimization of IRI-Plas model using the observed TEC values.

Advantages of the new model of IRI (IRI-Plas) to simulate the ionospheric electron density: case of the European area

Abstract. Satellite telecommunications, positioning and navigation systems require knowledge of the electron distribution in height Ne(h) to high-altitude orbits of satellites. One of the possibilities to construct such profiles is associated with the use of the ionospheric total electron content TEC. This paper is devoted to three advantages of the IRI-Plas model. They include introduction of the topside basis scale height Hsc, expansion of the IRI model to the plasmasphere, ingestion of experimental values of TEC. Testing of this model according to different satellite experiments (CHAMP, DMSP) shows the high efficiency of this model. The method of adaptation of the IRI-Plas model to the plasma frequency at altitudes of CHAMP and DMSP satellites allows us to produce behavior of Ne(h)-profiles during the disturbances, as well as to refine the values of TEC, which determine the accuracy of positioning. Results were obtained using data of the European area.

Comparison of model and experimental ionospheric parameters at high latitudes

Modern use and study of the auroral region needs to attract a wider class of models for describing conditions of radio wave propagation in the ionosphere. In this paper the possibilities of the International Reference Ionosphere model, well-proven and widespread in the mid-latitudes, are investigated in the high latitude zone. Model and measured values of the critical frequency foF2 for two mid-latitude stations (Juliusruh and Goosebay) and four high-latitude ones (Loparskaya, Sodankyla, Sondrestrom, Thule) are compared. Deviations of medians, variations from day to day and solar activity trends seemed to be similar for both areas. This similarity is irrespective of the RZ12 index. Special attention is paid to the TEC parameter and its determination using 6 versions of models, a new version of the model IRI2010 (IRI-Plas) among them. It is shown that the IRI-Plas model significantly improves the definition of TEC in contrast to the versions of IRI2007 and the new model NeQuick. The use of the median of the experimental equivalent slab thickness, together with the current values of the TEC, increases by a factor of two the agreement between calculated and measured foF2 values as compared with the variations from day to day. This allows foF2 to be defined in near-real time.

Use of TEC global maps and the IRI model to study ionospheric response to geomagnetic disturbances

Period of October–November 2003 provides a wide range of geomagnetic conditions. This paper looks at three intervals: a moderate magnetic disturbance (13–16.10.2003) and two intense magnetic storms (29–31.10 and 20–21.11). One purpose of this paper is to define the behavior of the two parameters of the ionosphere, foF2 (or NmF2) and TEC, in this period. Data of foF2 of European ionosondes and TEC values of global maps for the corresponding coordinates are used. The emphasis is on the study of the synchrony of these parameters, which determine the behavior of the proportionality factor τ(obs) between the TEC and NmF2. The second objective is to compare two methods of determining foF2 during the disturbances, using: (i) the STORM-factor of the IRI model, (ii) the median equivalent slab thickness τ(med), together with the global TEC maps. It is shown that synchrony of variations of TEC and NmF2 does not always exist, which leads to unpredictable behavior of τ(obs). Acceptable option of the calculation of foF2 from TEC is to use τ(med), ensuring compliance with the experimental data better than 0.5MHz in the case of synchrony, and 1.5MHz when it does not exist. The relationship between τ(obs) and the plasmaspheric part of the TEC of the IRI-Plas model is considered. A comprehensive investigation of this relationship in cases where no synchrony may contribute to the development of model of τ(obs) during the disturbances.

Inter-hemispheric imaging of the ionosphere with the upgraded IRI-Plas model during the space weather storms

International Reference Ionosphere extended to the plasmasphere (IRI-Plas) is upgraded analytically for assimilative mode of operation using GPS-derived Total Electron Content (TEC) for reconstruction of instantaneous ionospheric critical frequency and topside scale height at magnetic conjugate hemisphere. The performance of IRI-Plas code is examined with TECgps retrieved from Global Ionospheric Maps compared with the F2-layer critical frequency at eight ionosonde locations in East Asia region on both hemispheres during the space weather storms at solar maximum (2000) and solar minimum (2006). Missing ionosonde data are completed by cloning of critical frequency. Decomposition of TECgps in electron density profile with IRI-Plas code reveals the opposite relative changes of critical frequency and the topside scale height depending on solar activity. The ionospheric weather W index is computed for the desired locations in conjugate hemispheres and consistent results are obtained indicating the departure of instantaneous values of ionospheric parameters from their respective median varying from quiet state to intense storm.