Search

An accurate and reliable description of Earth’s ionosphere is of critical importance because of our increased reliance on satellite technology and the significant impact the ionosphere has on it.

The attempt of this work is to evaluate the three options (BSE-1979, AMTB-2013, SHU-2015) embedded in IRI-2016 for the F2 layer peak height (hmF2) estimation under low and high solar flux levels. We compare the model hmF2 with digisonde observations from Qaanaaq, Milllstone Hill, Ramey, Jicamarca and Port Stanley as well as Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation data over the five stations spanning from northern hemisphere to southern hemisphere. In the case of Millstone Hill, we also use incoherent scatter radar (ISR) measurements. For the comparison with digisonde data, SHU-2015 is the most accurate option for reproducing hmF2 at low and middle latitude stations (Milllstone Hill, Ramey, Jicamarca) with the smallest Root-Mean-Square-Error and the highest correlation with observations. At high latitude (Qaanaaq and Port Stanley), BSE-1979 becomes the best option. This is true for both low and high solar flux conditions. Similar results are obtained for the comparison between ISR and IRI-2016 hmF2 model options over Millstone Hill, where SHU-2015 option has the smallest deviations from the observation data in both low and high solar activity conditions. As for the comparison with COSMIC data, SHU-2015 edges out the other two options under low solar activity level with better performance at three stations. There is no optimal option under high solar activity level, which is to our surprise, cause SHU-2015 was developed based on a large amount of radio occultation data. At Jicamarca, all options show dramatic deviations from COSMIC observations, showing even negative correlations. We propose that the performance of the three options do not vary much with solar condition, while they differ a lot with location, for example, latitude.

With significant advancement in the climatological nature of the International Reference Ionosphere (IRI) through a series of editions, the ionospheric community now focuses on possible improvements in the IRI Real-Time Assimilative Model (IRTAM) for describing the real-time weather conditions in the ionosphere. In line with the focuses of the global research community, the present study intends improving the critical ionospheric electron density height (hmF2) predictions in the latest version of the IRI model (IRI-2016) through a comparative analysis with the hmF2 derived from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric occultation profiles over the African region under various solar and geomagnetic conditions. As the existing operational ionosondes (only five in number) are not evenly distributed across the African region, the dense COSMIC soundings offer an excellent opportunity for assessing the IRI hmF2 model performance over the region. The study includes a comparative study of observed COSMIC hmF2 values with IRI-2016 predictions, almost covering the whole solar cycle (2007 to 2017). The comparison is based on statistical model validation metrics for datasets under various solar and geomagnetic conditions. The average performance of the IRI hmF2 model over Africa is similar during quiet geomagnetic conditions under both low and high solar activity periods. However, the average performance declines during disturbed geomagnetic conditions and for night-time values, while the best average performance is noticed in the daytime hmF2 predictions. The SHU-2015 model option in IRI-2016 manifests the least prediction error, best model efficiency, and correlation with the COSMIC hmF2 values, justifying the use of a large number of COSMIC profiles in the development of the SHU-2015 model. Finally, the study suggests the suitability of the SHU-2015 IRI hmF2 option over the African region when and where there are no or limited COSMIC profiles. Additionally, the research work suggests further improvements in the IRI hmF2 predictions, especially for night-time values over the African region.

In situ measurements by the Low Earth Orbital (LEO) satellites, such as CHAMP, GRACE, and C/NOFS satellites have shown that the International Reference Ionosphere (IRI) model has shortcomings in describing the solar activity variation of the topside electron density. In particular IRI overestimates the measured densities in the topside ionosphere during the very low solar activity reached during the last solar minimum (2008–2009). We have used Alouette and ISIS topside sounder data and CHAMP, GRACE, as well as Swarm in situ measurements to deduce a correction term for the IRI electron density topside model that more accurately describes the variation with solar activity. We have used a linear variation with the solar index PF10.7 and described the latitudinal and altitudinal variation of the regression parameters A0 and A1 (intercept and slope). We find good agreement between the regression parameters deduced from the topside sounder and from the CHAMP and GRACE observations. Swarm results show the same latitudinal structure as the other data sets, however, a scaling factor is needed to obtain agreement of the absolute values. The new model was evaluated with Alouette and ISIS topside sounder, as well as LEO satellites in situ data showing a significant improvement over the current IRI model.

In this study, we perform the first comprehensive comparison of ion density (Ni) in the topside ionosphere measured by the Langmuir probe (LP) and faceplate (FP) of the thermal ion imager on board Swarm satellites. Our results show a systematic difference between the LP and FP derived Ni values, and the systematic difference shows prominent dependences on solar flux, local time, and season. Although both Ni datasets show generally good linear regression with electron density (Ne) measurements from the incoherent scatter radar (ISR) located at Jicamarca, the Ni derived from LP shows an additional dependence on the solar flux, while such a dependence cannot be seen in the FP-derived Ni. We suggest that the solar flux dependence of LP-derived Ni is related to the ion compositions change at Swarm altitude, which has not been properly accounted for in the LP processing algorithm. More light ions (e.g., H+), diffusing down from the plasmasphere to the Swarm altitude, seem to cause the overestimation of Ni from LP during low solar activity. A linear relation between the Swarm LP-derived Ni and ISR Ne is derived, and such a function is recommended to be implemented into further updates of the Swarm LP plasma density data.

This study presents a suggestion for improvement of the ion temperature (Ti) model in the International Reference Ionosphere (IRI). We have re-examined ion temperature data (primarily available from NASA’s Space Physics Data Facility (SPDF)from older satellites and combined them with newly available data from the Defense Meteorological Satellite Program (DMSP), the Communication Navigation Outage Forecasting System (C/NOFS), and from the recently launched Ionospheric Connection Explorer (ICON). We have compiled these data into a unified database comprising in total Ti data from 18 satellites. By comparisons with long term records of ion temperature from the three incoherent scatter radars (ISRs) (Jicamarca, Arecibo, and Millstone Hill), it was found that an intercalibration is needed to achieve consistency with the ISR data and among individual satellite data sets. This database with thus corrected data has been used for the development of a new global empirical model of Ti with inclusion of solar activity variation. This solar activity dependence is represented by an additive correction term to the Ti global pattern. Due to the limited data coverage at altitudes above 1000 km, the altitude range described by the model ranges from 350 km to 850 km covering only the region where generally Ti is higher than the neutral temperature (Tn) and lower than the electron temperature (Te). This approach is consistent with the current description of Ti in the IRI model. However, instead of one anchor point at 430 km altitude as in the current IRI, our approach includes anchor points at 350, 430, 600, and 850 km. At altitudes above 850 km Ti is merged using a gradient derived from the model at 600 and 850 km, with the electron temperature described by the IRI-2016/TBT-2012 option. Comparisons with the ISR data (Jicamarca, Arecibo, Millstone Hill, and Kharkiv) for high and low solar activity and equinox show that the proposed Ti model captures local time variation of Ti at different altitudes and latitudes better than the current IRI-2016 Ti model.

Real-time assimilative empirical models based on the International Reference Ionosphere (IRI) [1], a 3D quiet-time climatology model of the ionospheric plasma density, provide prompt weather specification by adjusting IRI definitions into a better match with the available measurements and geospace activity indicators [2]. The IRI-based Real-Time Assimilative Model (IRTAM) [3] is one of such Real-Time IRI operational ionospheric weather models based on the low-latency sensor inputs from the Global Ionosphere Radio Observatory (GIRO) [4].IRTAM leverages predictive properties of the underlying IRI expansion basis formalism [5] that treats dynamics of the ionospheric plasma in terms of its harmonics, both temporal and spatial. It uses Non-linear Error Compensation Technique with Associative Restoration (NECTAR) technique [6] to first detect multi-scale inherent diurnal periodicity of the differences between GIRO measurements and the underlying IRI climatology. Then, under the assumption that variations in time at periodic, planetary-scale Eigen scales (diurnal, half-diurnal, 8-hour, etc.) translate to their spatial properties, it globally interpolates and extrapolates each diurnal harmonic individually. This approach allowed NECTAR to associate observed fragments of the activity at GIRO locations with the unveiling grand-scale weather processes of the matching variability scales, as the ground observatories co-rotate with the Earth.Predictive properties of IRTAM are discussed in order to establish the baseline predictability of the ionospheric dynamics that analyzes only the latest 24-hour history of its deviation from the expected behavior. Concepts for the next generation empirical forecast models are outlined that would leverage the same principle of associative restoration to evaluate the geospace activity timeline and its subtle associations with subsequent storm-time behavior of the ionosphere.References[1] Bilitza, D. (ed.) (1990), International Reference Ionosphere 1990, 155 pages, National Space Science Data Center, NSSDC/WDC-A-R&S 90-22, Greenbelt, Maryland, November 1990.[2] Bilitza, D., D. Altadill, V. Truhlik, V. Shubin, I. Galkin, B. Reinisch, and X. Huang (2017), International Reference Ionosphere 2016: From ionospheric climate to real-time weather predictions, Space Weather, 15, 418-429, doi:10.1002/2016SW001593.[3] Galkin, I. A., B. W. Reinisch, X. Huang, and D. Bilitza (2012), Assimilation of GIRO Data into a Real-Time IRI, Radio Sci., 47, RS0L07, doi:10.1029/2011RS004952.[4] Reinisch, B.W. and I.A. Galkin (2011), Global Ionospheric Radio Observatory (GIRO), Earth Planets Space, vol. 63 no. 4 pp. 377-381, doi:10.5047/eps.2011.03.001[5] International Telecommunications Union (2009), ITU-R reference ionospheric characteristics, Recommendation P.1239-2 (10/2009). Retrieved from http://www.itu.int/rec/R-REC-P.1239/en.[6] Galkin, I. A., B. W. Reinisch, A. Vesnin, et al., (2020) Assimilation of Sparse Continuous Near-Earth Weather Measurements by NECTAR Model Morphing, Space Weather, 18, e2020SW002463, doi:10.1029/2020SW002463.

The Space Physics Data Facility (SPDF https://spdf.gsfc.nasa.gov), as the non-solar NASA Heliophysics active final archive, works with current operating missions and the heliophysics community to i...

Non-linear Error Compensation Technique with Associative Restoration (NECTAR) is a novel approach to the assimilation of fragmentary sensor data to produce a global nowcast of the near-Earth space weather. NECTAR restores missing information by iteratively transforming (“morphing”) an underlying global climatology model into agreement with currently available sensor data. The morphing procedure benefits from analysis of the inherent multiscale diurnal periodicity of the geosystems by processing 24-hr time histories of the differences between measured and climate-expected values at each sensor site. The 24-hr deviation time series are used to compute and then globally interpolate the diurnal deviation harmonics. NECTAR therefore views the geosystem in terms of its periodic planetary-scale basis to associate observed fragments of the activity with the grand-scale weather processes of the matching variability scales. Such approach strengthens the restorative capability of the assimilation, specifically when only a limited number of observatories is available for the weather nowcast. Scenarios where the NECTAR concept works best are common in planetary-scale near-Earth weather applications, especially where sensor instrumentation is complex, expensive, and therefore scarce. To conduct the assimilation process, NECTAR employs a Hopfield feedback recurrent neural network commonly used in the associative memory architectures. Associative memories mimic human capability to restore full information from its initial fragments. When applied to the sparse spatial data, such a neural network becomes a nonlinear multiscale interpolator of missing information. Early tests of the NECTAR morphing reveal its enhanced capability to predict system dynamics over no-data regions (spatial interpolation). Por pares

The Space Physics Data Facility (SPDF https://spdf.gsfc.nasa.gov) and Solar Data Analysis Center (SDAC https://umbra.nascom.nasa.gov/), as the NASA Heliophysics active final archives, will be prese...

A new monthly ionospheric index, IG NS , is presented to improve the representation of the solar cycle variation of the ionospheric F2 peak plasma frequency, foF2. IG NS is calculated using a methodology similar to the construction of the ”global effective sunspot number”, IG, given by Liu et al. (1983) but selects ionosonde observations based on hemispheres. We incorporated the updated index into the International Reference Ionosphere (IRI) model and compared the foF2 model predictions with global ionospheric observations. We also investigated the influence of the underlying foF2 model on the IG index. IRI has two options for foF2 specification, the CCIR-66 and URSI-88 foF2 models. For the first time, we have calculated IG using URSI-88 and assessed the impact on model predictions. Through a retrospective model-data comparison, results show that the inclusion of the new monthly IG NS index in place of the current 12-month smoothed IG index reduce the foF2 model prediction errors by nearly a factor of two. These results apply to both day-time and nightime predictions. This is due to an overall improved prediction of foF2 seasonal and solar cycle variations in the different hemispheres.

Improvements in representation of foE for use in the International Reference Ionosphere (IRI) model are investigated. The IRI model currently depends on the 12-month running mean of sunspot number to estimate the foE. Using the F10.7 daily and F10.7_81 indices as the new model drivers, results are compared to ionosonde measurements at low, mid and high latitudes during solar minimum and solar maximum. Results show that the IRI model estimates the foE parameter better at low-mid latitudes than at high latitudes, specifically during solar maximum. Using the F10.7 indices to derive the IRI model improves estimates of foE, specifically at low-mid latitudes. The F10.7_81 index was found to perform better than the daily F10.7 index. Improvements during solar maximum and during solar minimum were on average 3.5% and 1%, respectively. Therefore, the F10.7_81 index is recommended as IRI model driver for foE estimates.

The paper presents the latest version of the International Reference Ionosphere model (IRI-2016) describing the most important changes and improvements that were included with this version and discussing their impact on the IRI predictions of ionospheric parameters. IRI-2016 includes two new model options for the F2 peak height hmF2 and a better representation of topside ion densities at very low and high solar activities. In addition, a number of smaller changes were made concerning the use of solar indices and the speedup of the computer program. We also review the latest developments toward a Real-Time IRI. The goal is to progress from predicting climatology to describing the real-time weather conditions in the ionosphere.

This paper gives a brief overview over the International Reference Ionosphere (IRI) project and model. IRI is recognized as the official standard for the ionosphere by the International Standardization Organization (ISO), the International Union of Radio Science (URSI), the Committee on Space Research (COSPAR), and the European Cooperation for Space Standardization (ECCS). Of great importance are the external drivers of the model that help IRI to represent ionospheric conditions as realistically as possible. The paper discusses the drivers currently used presents recent improvements and changes. Besides the standard solar, magnetic, and ionospheric indices the paper also reports on the adjustment of the model with data and equivalent indices and on the progress towards a Real-Time IRI using data assimilation. IRI has been widely validated with many different data sources and has fared very well in community wide assessment studies. We present some of these studies and document the wide usages of the model in the scientific literature. Finally, we present an outlook on things to come in IRI-2018 and thereafter.

Selected original analog telemetry tapes from three of the topside-sounder satellites of theInternational Satellites for Ionospheric Studies (ISIS) program, namely Alouette 2, ISIS I, and ISIS II, wereused in an earlier project to produce more than ½ million digital topside ionograms; the resulting digitaltopside ionograms from ISIS II were used to produce more than 86,000 globally distributed vertical topsideionospheric electron density profiles Ne(h) that cover a time span of more than a solar cycle. These Ne(h) wereproduced using the Topside Ionogram Scaler with True height algorithm auto-scaling software. Beforeattempting to automatically process Alouette-2 or ISIS-I ionograms, a data-enhancement project wasinitiated so as to increase the number of ionograms suitable for manual scaling and to increase theauto-processing success rate. These enhancements were mainly to correct problems that often occurredduring the analog-to-digital conversion of the original telemetry tapes. Here we illustrate the improvementsmade to the ISIS-I digital topside ionograms and compare Ne values at the satellite altitude and Ne(h)profiles, based on the manual scaling of selected ionograms, to both the auto-scaled values and thepredictions of the International Reference Ionosphere 2016 model. The results indicate the need to improvethe available auto-processing software for the new ISIS-I digital ionograms and that International ReferenceIonosphere 2016 predicts midlatitude winter topside Ne values that are too high in the late morning andat noon but too low in the early morning.

Large magnetic-storm-induced changes were detected in high-latitude topside vertical electron density profiles Ne(h) in a database of profiles and digital topside ionograms, from the International Satellites for Ionospheric Studies (ISIS) program, that enabled Ne(h) profiles to be obtained in nearly the same region of space before, during, and after a major magnetic storm (Dst -100nT). Storms where Ne(h) profiles were available in the high-latitude Northern Hemisphere had better coverage of solar wind parameters than storms with available Ne(h) profiles in the high-latitude Southern Hemisphere. Large Ne(h) changes were observed during all storms, with enhancements and depletions sometimes near a factor of 10 and 0.1, respectively, but with substantial differences in the responses in the two hemispheres. Large spatial andor temporal Ne(h) changes were often observed during Dst minimum and during the storm recovery phase. The storm-induced Ne(h) changes were the most pronounced and consistent in the Northern Hemisphere in that large enhancements were observed during winter nighttime and large depletions during winter and spring daytime. The limited available cases suggested that these Northern Hemisphere enhancements increased with increases of the time-shifted solar wind velocity v, magnetic field B, and with more negative values of the B components except for the highest common altitude (1100km) of the profiles. There was also some evidence suggesting that the Northern Hemisphere depletions were related to changes in the solar wind parameters. Southern Hemisphere storm-induced enhancements and depletions were typically considerably less with depletions observed during summer nighttime conditions and enhancements during summer daytime and fall nighttime conditions.

Recommendations of the International Reference Ionosphere (IRI) Workshop 2017 in Taoyuan City, Taiwan and International GNSS Service (IGS) Workshop 2018 in Wuhan, China included establishment of an ionosphere mapping service that would fuse measurements from two independent sensor networks: IGS permanent GNSS receivers providing the vertical total electron content (VTEC) measurements and ionosondes of the Global Ionosphere Radio Observatory (GIRO) that compute the bottomside vertical profiles of the ionospheric plasma density. Using available GAMBIT software at GIRO, we introduced new VTEC products to its data roster: previously unavailable global average (climate) maps of VTEC and slab thickness based on climatological capabilities of IRI. Incorporation of the VTEC and τ maps into the GAMBIT Explorer environment provided data analysts with nearly 10-year history of the reference average VTEC records and opened access to the GAMBIT toolkit for evaluation and validation of the τ computations. This result is the first step towards establishing an infrastructure and the data workflow to provide GAMBIT users with the low latency and consistent quality and usability of the ionospheric weather-climate specifications. Combination of IGS-provided VTEC and GIRO-provided peak density of F2 layer NmF2 allows ground-based evaluation of the equivalent slab thickness τ, a derived property of the near-Earth plasma that characterizes the skewness of its vertical profile up to the GNSS spacecraft altitudes.

The annual anomaly is the ionospheric phenomena in which the globally-averaged electron density is greater in January than it is in July. This anomaly causes the ionospheric solsticial variation – a variation with a periodicity of one year that is in-phase with the January solstice – to be more pronounced over the Northern Hemisphere than the Southern Hemisphere. Predictions of the magnitude of annual anomaly using the International Reference Ionosphere (IRI) model have been shown to be unreliable so far. The objective of our study is to investigate model prediction of the magnitude of the annual ionospheric anomaly using new ionospheric indices as inputs in the IRI model. These new indices improve predictions ionospheric variations that differ over the two hemispheres. We present a retrospective analysis of the IRI predictions of the ionospheric daytime annual anomaly and solsticial variation using a model-data comparison with observations from over 40 ionosondes for high, moderate, and low solar cycle conditions. Our results show that there is an overall 33 % underestimation of the magnitude of the annual anomaly when the by the IRI. When the new ionospheric indices as used in the IRI, model predictions underestimate the magnitude of the annual anomaly by 6 %. This indicates an improvement of the model predictions when using the new indices. We show that the underestimation of the annual anomaly by IRI is related to a similar underestimation of the magnitude of the ionospheric solsticial variation over the Northern Hemisphere. Based on our results, we infer that the underlying processes of the annual anomaly must vary across each hemisphere.

APID5196071. Provided with near real-time sensor data, AEMs become useful in applications that rely on an accurate ionospheric weather nowcast. We make another step towards extending the AEM scope to the forecast applications that require knowledge of the ionospheric conditions over next several days. Development of such forecast capability has to emphasize processes that are not local and rethink the reference frame and coordinate system for its representations of the ionospheric dynamics from corotating to solar synchronous frame. We discuss details of the proposed expansion basis functions for implementation in forecasting AEMs.

To address challenges of assessing space weather modeling capabilities, the CommunityCoordinated Modeling Center is leading a newly establishedInternational Forum for Space WeatherModeling Capabilities Assessment. This paper presents preliminary results of validation of modeled foF2 (F2 layer critical frequency) and TEC (total electron content) during the first selected 2013 March storm event (17 March 2013). In this study, we used eight ionospheric models ranging from empirical to physics-based, coupled ionosphere-thermosphere and data assimilation models. The quantities we considered are TEC and foF2 changes and percentage changes compared to quiet time background, and the maximum and minimum percentage changes. In addition, we considered normalized percentage changes of TEC. We compared the modeled quantities with ground-based observations of vertical Global Navigation SatelliteSystem TEC (provided by Massachusetts Institute of Technology Haystack Observatory) and foF2 data (provided by Global Ionospheric Radio Observatory) at the 12 locations selected in middle latitudes of the American and European-African longitude sectors. To quantitatively evaluate the models’ performance, we calculated skill scores including correlation coefficient, root-mean square error (RMSE), ratio of the modeled to observed maximum percentage changes (yield), and timing error. Our study indicates that average RMSEs of foF2range from about 1 MHz to 1.5 MHz. The average RMSEs of TEC are between ~5 and ~10 TECU (1 TEC Unit= 1016el/m2). dfoF2[%] RMSEs are between 15% and 25%, which is smaller than RMSE of dTEC[%] ranging from30% to 60%. The performance of the models varies with the location and metrics considered.

This paper describes the latest version of the International Reference Ionosphere (IRI) model. IRI-2012 includes new models for the electron density and ion densities in the region below the F-peak, a storm-time model for the auroral E-region, an improved electron temperature model that includes variations with solar activity, and for the first time a description of auroral boundaries. In addition, the thermosphere model required for baseline neutral densities and temperatures was upgraded from MSIS-86 to the newer NRLMSIS-00 model and Corrected Geomagnetic coordinates (CGM) were included in IRI as an additional coordinate system for a better representation of auroral and polar latitudes. Ongoing IRI activities towards the inclusion of an improved model for the F2 peak height hmF2 are discussed as are efforts to develop a “Real-Time IRI”. The paper is based on an IRI status report presented at the 2013 IRI Workshop in Olsztyn, Poland. The IRI homepage is at IRImodel.org .

We present a revision of the ion composition model that is included in the International Reference Ionosphere (IRI) as the TTS-03 option. We employed a better description of the solar activity variation based on the assumption that the dependence of the logarithm of absolute densities of the individual ion species (H+, O+, He+ and N+) on the F10.7 index is linear. Unlike the TTS-03 model using the relative ion densities, the revised model employs absolute ion densities measured by the Atmosphere Explorer C&E and Intercosmos-24 satellites. Results of the revised ion composition model are presented, with special emphasis on the upper transition height (HT) during low solar activity. Equatorial HT produced by the model for a very low solar activity is ∼800 km at daytime (14 h LT) and ∼520 km at nighttime (2 h LT). These values are closer to HT observed by the Coupled Ion-Neutral Dynamics Investigations (CINDI) on the Communications/Navigation Outage Forecasting System (C/NOFS) satellite in the years 2008 and 2009 (minimum solar activity of the 23rd solar cycle) than the IRI-2007 and IRI-2012 options for the ion composition. A comparison of the options for the ion composition with the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) is also shown.

In order to assess current modeling capability of reproducing storm impacts on total electron content (TEC), we considered quantities such as TEC, TEC changes compared to quiet time values, and the maximum value of the TEC and TEC changes during a storm. We compared the quantities obtained from ionospheric models against ground-based GPS TEC measurements during the 2006 AGU storm event (14-15 December 2006) in the selected eight longitude sectors. We used 15 simulations obtained from eight ionospheric models, including empirical, physics-based, coupled ionosphere-thermosphere, and data assimilation models. To quantitatively evaluate performance of the models in TEC prediction during the storm, we calculated skill scores such as RMS error, Normalized RMS error (NRMSE), ratio of the modeled to observed maximum increase (Yield), and the difference between the modeled peak time and observed peak time. Furthermore, to investigate latitudinal dependence of the performance of the models, the skill scores were calculated for five latitude regions. Our study shows that RMSE of TEC and TEC changes of the model simulations range from about 3 TECU (total electron content unit, 1 TECU = 1016 el m2) (in high latitudes) to about 13 TECU (in low latitudes), which is larger than latitudinal average GPS TEC error of about 2 TECU. Most model simulations predict TEC better than TEC changes in terms of NRMSE and the difference in peak time, while the opposite holds true in terms of Yield. Model performance strongly depends on the quantities considered, the type of metrics used, and the latitude considered.

When the Committee on Space Research (COSPAR) initiated the International Reference Ionosphere (IRI) project in 1968 it wisely selected K. Rawer as its first Chairperson. With a solid footing and good contacts in both the ground-based and space-based ionospheric communities he was ideally suited to pull together colleagues and data from both communities to help build the first version of the IRI. He assembled a team of 20+ international ionospheric experts in the IRI Working Group and chaired and directed the group from 1968 to 1984. The working group has now grown to 63 members and the IRI model has undergone many revisions as new data became available and new modeling techniques were applied. This paper was presented during a special session of the Kleinheubach Tagung 2013 in honor of K. Rawer's 100th birthday. It will review the current status of the IRI model and project and the international recognition it has achieved. It is quite fitting that this year we not only celebrate K. Rawer's 100th birthday but also the exciting news that his favorite science endeavor, IRI, has been internationally recognized as an ISO (International Standardization Organization) standard. The IRI homepage is at http://irimodel.org.

Orbiting Geophysical Observatory 5 (OGO 5) magnetospheric ion-composition data (H+, He+ and O+) from an ion spectrometer (Sharp, 1969) have been retrieved from old magnetic tapes archived at the National Space Science Data Center (NSSDC). The highly compressed binary format was converted into a user-friendly ASCII format and these data have been made available online. We have inspected reliability and consistency of this data set in state of the art current knowledge. Comparing with the climatological model IRI-2012 and the mathematical model FLIP a shift of absolute and relative ion densities with time was revealed. We have suggested a correction procedure of individual H+, He+ and O+ ion densities. Using the corrected data set, we investigated plasmapause locations based on density gradient in H+, and He+. Correlation coefficient of both locations was determined as approx. 0.886 and the typical difference (Delta)L approx. 0.1. The electron density at the He+ plasmapause location for all cases is >100/cu cm.

The recent availability of new data sets during the recent extreme solar minimum provides an opportunity for testing the performance of the International Reference Ionosphere in historically under-sampled regions. This study will present averages and variability of topside ionospheric densities over Africa as a function of season, local time, altitude, and magnetic dip latitude as measured by the Coupled Ion-Neutral Dynamics Investigation (CINDI) Mission of Opportunity on the C/NOFS satellite. The results will be compared to the three topside model options available in IRI-2007. Overall, the NeQuick model is found to have the best performance, though during the deepest part of the solar minimum all three options significantly overestimate density.

The height, hmF2, and the electron density, NmF2, of the F2 peak are key model parameters to characterize the actual state of the ionosphere. These parameters, or alternatively the propagation factor, M3000F2, and the critical frequency, foF2, of the F2 peak, which are related to hmF2 and NmF2, are used to anchor the electron density vertical profile computed with different models such as the International Reference Ionosphere (Bilitza, 2002), as well as for radio propagation forecast purposes. Long time series of these parameters only exist in an inhomogeneous distribution of points over the surface of Earth, where dedicated instruments (typically ionosondes) have been working for many years. A commonly used procedure for representing median values of the aforementioned parameters all over the globe is the one recommended by the ITU-R (ITU-R, 1997). This procedure, known as the Jones and Gallet mapping technique, was based on ionosondes measurements gathered from 1954 to 1958 by a global network of around 150 ionospheric stations (Jones and Gallet, 1962; Jones and Obitts, 1970). Even though several decades have passed since the development of that innovative work, only few efforts have been dedicated to establish a new mapping technique for computing hmF2 and NmF2 median values at global scale or to improve the old method using the increased observational database. Therefore, in this work three different procedures to describe the daily and global behavior of the height of the F2 peak are presented. All of them represent a different and simplified method to estimate hmF2 and are based on different mathematical expressions. The advantages and disadvantages of these three techniques are analyzed, leading to the conclusion that the recommended procedure to represent hmF2 is best characterized by a Spherical Harmonics expansion of degree and order equal to 15, since the differences between the hmF2 values obtained with the Jones and Gallet technique and those obtained using the abovementioned procedure are of only 1%. 2013 COSPAR. Published by Elsevier Ltd. All rights reserved. Fil: Brunini, Claudio Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas. Grupo de Geodesia Espacial y Aeronomia; Argentina Fil: Conte, Juan Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas. Grupo de Geodesia Espacial y Aeronomia; Argentina Fil: Azpilicueta, Francisco Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas. Grupo de Geodesia Espacial y Aeronomia; Argentina Fil: Bilitza, Dieter. National Aeronautics and Space Administration; Estados Unidos

Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region electron densities. The empirical model is called STORM-E and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). The proxy for characterizing the E-region response to geomagnetic forcing is NO+(v) Volume Emission Rates (VER) derived from the TIMED/SABER 4.3 μm channel limb radiance measurements. The storm-time response of the NO+(v) 4.3 μm VER is most sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO+(v) 4.3 μm VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known nighttime quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part I of this series gives a detailed description of the algorithms and methodologies used to derive NO+(v) VER from SABER 4.3 μm limb emission measurements. In this paper, Part II of the series, the development of the E-region electron density storm-time correction factor is described. The STORM-E storm-time correction factor is fit to a single geomagnetic index. There are four versions of the STORM-E model, which are currently independent of magnetic local time. Each version is fit to one of the following indices: HP, AE, Ap, or Dst. High-latitude Incoherent Scatter Radar (ISR) E-region electron density measurements are compared to STORM-E predictions for various geomagnetic storm periods during solar cycle 23. These comparisons show that STORM-E significantly improves the prediction of E-region electron density enhancements due to auroral particle precipitation, in comparison to the nominal IRI model or to the quiet-time baseline electron density concentrations measured by ISR. The STORM-E/ISR comparisons indicate that the STORM-E fits to the Ap-, AE-, and HP-indices are comparable in both absolute accuracy and relative dynamical response. Contrarily, the Dst-index does not appear to be a suitable input driver to parameterize the E-region electron density response to geomagnetic activity.

In this paper, we examine the nighttime ionosphere climatology structure in the low latitude region and discrepancies between Global Ultraviolet Imager (GUVI) observations and the IRI model predictions using (1) the magnetic zonal mean of electron number density as a function of altitude and magnetic latitude, (2) vertical electron density profiles at various levels of F10.7 index, (3) nighttime descent and magnitude decrease of the ionosphere, (4) point-to-point comparisons of F-peak height (hmF2) and density (NmF2), and (5) the magnetic longitudinal variations of hmF2 and NmF2. The data collected from the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission since its launch in December 2001 have provided great opportunities for many scientific investigations of the ionosphere. In this analysis, we investigate the climatology of the nighttime low-latitude ionosphere under low geomagnetic activity (kp ⩽ 4) using the electron density profiles inferred from the airglow measurements obtained by the GUVI aboard the TIMED spacecraft and compared with the results obtained from IRI (International Reference Ionosphere) model-2001. The observed climatology is an essential tool for further understanding the electrodynamics in the low-latitude region and improving the model’s prediction capability. The time range of the GUVI data used in this study is from 2002 (day 053) to 2006 (day 304), and the IRI model predictions were produced at every GUVI location. The ionosphere observed is generally of greater density than what IRI predicts throughout the night for all four seasons for low and moderate solar activity while the model over-predicts the electron density near the F-region peak at high solar activity before midnight. Observations show that the height of the F-region peak has a steep descent from dusk to midnight and near midnight the height of layer is insensitive to solar conditions, significantly different than what is predicted by IRI. Longitudinal features shown in GUVI data are present in the low-latitude ionosphere after sunset and continue through to midnight after which the low-latitude ionosphere is largely zonally symmetric.

Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region peak electron densities. The empirical model is called STORM-E and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). The proxy for characterizing the E-region response to geomagnetic forcing is NO + (v) volume emission rates (VER) derived from the TIMED/SABER 4.3 μm channel limb radiance measurements. The storm-time response of the NO + (v) 4.3 μm VER is sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO + (v) 4.3 μm VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part II of this series describes the explicit development of the empirical storm-time correction factor for E-region peak electron densities, and shows comparisons of E-region electron densities between STORM-E predictions and incoherent scatter radar measurements. In this paper, Part I of the series, the efficacy of using SABER-derived NO + (v) VER as a proxy for the E-region response to solar-geomagnetic disturbances is presented. Furthermore, a detailed description of the algorithms and methodologies used to derive NO + (v) VER from SABER 4.3 μm limb emission measurements is given. Finally, an assessment of key uncertainties in retrieving NO + (v) VER is presented.

The unusually deep and extended solar minimum of cycle 2324 made it very difficult to predict the solar indices 1 or 2 years into the future. Most of the predictions were proven wrong by the actual observed indices. IRI gets its solar, magnetic, and ionospheric indices from an indices file that is updated twice a year. In recent years, due to the unusual solar minimum, predictions had to be corrected downward with every new indices update. In this paper we analyse how much the uncertainties in the predictability of solar activity indices affect the IRI outcome and how the IRI values calculated with predicted and observed indices compared to the actual measurements.Monthly median values of F2 layer critical frequency (foF2) derived from the ionosonde measurements at the mid-latitude ionospheric station Juliusruh were compared with the International Reference Ionosphere (IRI-2007) model predictions. The analysis found that IRIprovides reliable results that compare well with actual measurements, when the definite (observed and adjusted) indices of solar activityare used, while IRI values based on earlier predictions of these indices noticeably overestimated the measurements during the solar minimum.One of the principal objectives of this paper is to direct attention of IRI users to update their solar activity indices files regularly.Use of an older index file can lead to serious IRI overestimations of F-region electron density during the recent extended solar minimum.

Cycle 23 was exceptional in that it lasted almost two years longer than its predecessors and in that it ended in an extended minimum period that proved all predictions wrong. Comparisons of the International Reference Ionosphere (IRI) with CHAMP and GRACE in-situ measurements of electron density during the minimum have revealed significant discrepancies at 400–500 km altitude ( Luhr and Xiong, 2010) . Our study investigates the causes for these discrepancies with the help of ionosonde and Planar Langmuir Probe (PLP) data from the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. Our C/NOFS comparisons confirm the earlier CHAMP and GRACE results. But the ionosonde measurements of the F-peak plasma frequency (foF2) show generally good agreement throughout the whole solar cycle. At mid-latitude stations yearly averages of the data-model difference are within 10% and at low latitudes stations within 20%. The 60–70% differences found at 400–500 km altitude are not seen at the F peak. We will discuss how these seemingly contradicting results from the ionosonde and insitu data-model comparisons can be explained and which parameters need to be corrected in the IRI model.

A data-base of electron temperature (Te) comprising of most of the available LEO satellite measurements in the altitude range from 350 to 2000 km has been used for the development of a new global empirical model of Te for the International Reference Ionosphere (IRI). For the first time this will include variations with solar activity. Variations at five fixed altitude ranges centered at 350, 550, 850, 1400, and 2000 km and three seasons (summer, winter, and equinox) were represented by a system of associated Legendre polynomials (up to the 8th order) in terms of magnetic local time and the earlier introduced invdip latitude. The solar activity variations of Te are represented by a correction term of the Te global pattern and it has been derived from the empirical latitudinal profiles of Te for day and night (Truhlik et al., 2009a). Comparisons of the new Te model with data and with the IRI 2007 Te model show that the new model agrees well with the data generally within standard deviation limits and that the model performs better than the current IRI Te model.

The in situ measurements of electron contents from GRACE K-band (dual-frequency) ranging system and CHAMP planar Langmuir probe were used to validate the international reference ionosphere (IRI) models. The comparison using measurements from year 2003 to 2007 shows a general agreement between data and the model outputs. The improvement in the newer IRI model (IRI-2007) is evident with the measurements from the GRACE satellites orbiting at the higher altitude. We present the comparison between the models and data comprehensively for various cases in solar activity, local time, season, and latitude. The IRI models do not well predict the electron density in the years 2006 and later, when the solar activity is extremely low. The IRI models generally overestimate the electron density during local winter while they underestimate during local summer. In the equatorial region, the large difference at local sunrise lasts for all years and all seasons. The IRI models do not perform well in predicting the anomaly in the polar region such as the Weddell Sea Anomaly. These discrepancies are likely due to smoothed (12-month averaged) solar activity indices used in the IRI models and due to insufficient spherical harmonic representation not able to capture small spatial scales. In near future, further improvement on the IRI models is expected by assimilating those in situ satellite data by implementing higher resolution (spatial and temporal) parameterizations.

During the International Polar Year (IPY) two Incoherent Scatter Radars (ISRs) achieved close to 24/7 continuous observations. This presentation describes their data sets and specifically how they can provide the International Reference Ionosphere (IRI) a fiduciary E- and F-region ionosphere description for solar minimum conditions in both the auroral and polar cap regions. The ionospheric description being electron density, ion temperature and electron temperature profiles from as low as 90 km extending to several scale heights above the F-layer peak. The auroral location is Poker Flat in Alaska at 65.1 N latitude, 212.5 E longitude where the NSF s new Poker Flat Incoherent Scatter Radar (PFISR) is located. This location during solar minimum conditions is in the auroral region for most of the day but is at midlatitudes, equator ward of the cusp, for about 4-8 h per day dependent upon geomagnetic activity. In contrast the polar location is Svalbard, at 78.2 N latitude, 16.0 E longitude where the EISCAT Svalbard Radar (ESR) is located. For most of the day the ESR is in the Northern Polar Cap with a noon sector passage often through the dayside cusp. Of unique relevance to IRI is that these extended observations have enabled the ionospheric morphology to be distinguished between quiet and disturbed geomagnetic conditions. During the IPY year, 1 March 2007 - 29 February 2008, about 50 solar wind Corotating Interaction Regions (CIRs) impacted geospace. Each CIR has a two to five day geomagnetic disturbance that is observed in the ESR and PFISR observations. Hence, this data set also enables the quiet-background ionospheric climatology to be established as a function of season and local time. These two separate climatologies for the ion temperature at an altitude of 300 km are presented and compared with IRI ion temperatures. The IRI ion temperatures are about 200-300 K hotter than the observed values. However, the MSIS neutral temperature at 300 km compares favorably with the quiet-background in temperature, both in magnitude and climatology.

We present a new technique for improving ionospheric models of nighttime E-region electron densities under geomagnetic storm conditions using TIMED/SABER measurements of broadband 4.3 lm limb radiance. The response of E-region electron densities to geomagnetic activity is characterized by SABER-derived NO + (v) 4.3 lm Volume Emission Rates (VER). A storm-time E-region electron density correction factor is defined as the ratio of storm-enhanced NO + (v) VER to a quiet-time climatological average NO + (v) VER, which will be fit to a geomagnetic activity index in a future work. The purpose of this paper is to demonstrate the feasibility of our technique in two ways. One, we compare storm-to-quiet ratios of SABER-derived NO + (v) VER with storm-to-quiet ratios of electron densities measured by Incoherent Scatter Radar. Two, we demonstrate that NO + (v) VER can be parameterized by widely available geomagnetic activity indices. The storm-time correction derived from NO + (v) VER is applicable at high-latitudes.

The paper describes the method and initial results of assimilating the auroral peak E-region density (NmE) and the auroral equatorward boundary (EB) into the International Reference Ionosphere (IRI). The NmE and EB are obtained using a FUV based auroral model or FUV measurements in near real-time. Initial results show that the auroral NmE is often significantly larger than the NmE due to the solar EUV. This indicates the importance of including the contribution of precipitating electrons in IRI. The global equatorial boundary helps to improve the specification of the sub-auroral ionosphere trough in IRI. An IDL software package has been developed to interactively display the IRI parameters with assimilated NmE and EB. It can serve as an operational tool for space weather monitoring.

The ionospheric characteristics of the F2 layer peak have been measured with ionosondes from the ground or with satellites from space. The most common characteristics are the F2-peak density NmF2 and peak height hmF2. In addition to these two parameters this paper studies the F2-peak scale height. Comparing the median values of hmF2 and NmF2 obtained from topside and bottomside sounding shows good agreement in general. The Chapman scale height values for the F2 layer peak derived from topside profiles, Hm,top, are generally several times larger than Hm,bot derived from bottomside profiles.