Time-dependent Ionospheric Model Research Articles

Minimizing NeQuick TEC prediction error via data ingestion at three African equatorial stations

NeQuick model is a three dimensional and time dependent ionospheric electron density model that gives as output electron density profile N(h) and via integration the slant TEC (sTEC) for any particular locations on the globe. The model requires as input solar ionizing index in addition to the coordinates of the ray points. The index being used as a proxy to the EUV which is responsible for the ionization of the upper atmosphere is either the smoothed sunspot numbers (R12) or the 10.7 cm solar radio noise flux (F10.7 ). The closer the values of the proxy index to the EUV value, the better the performance of the NeQuick model. We have therefore investigated the improvement of NeQuick via optimization of the F10.7 index using GPS sTEC derived data from three stations in the equatorial region of the African sector. In order to achieve this, the root mean square of the difference between the modeled and the observed sTEC values were calculated for a range of values of F10.7, and via optimization, the effective F10.7 index (i.e. the one that gives the minimum root mean square error or the one that minimizes the error between the observed and the modeled) was obtained for a particular day and for a particular station. The value obtained (i.e. F10.7 effective ), which is a station based value, is then used as ionization index into the NeQuick model for the next two consecutive days. The results obtained showed an improvement in the model performance for these two days although that of the first day, in most cases, is better than that of the second day.

How uncertainty in the neutral wind limits the accuracy of ionospheric modeling and forecasting

AbstractOne of the most important input fields for an ionospheric model is the horizontal neutral wind. The primary mechanism by which the neutral wind affects ionospheric densities is the inducement of an upward or downward ion drift along the magnetic field lines; this affects the rate at which ions are lost through recombination. The magnitude of this effect depends upon the dip angle of the magnetic field; for this reason, the impact of the neutral wind is somewhat less in polar regions than at mid‐latitudes. It is unfortunate that observations of the neutral wind are relatively scarce, as compared for example with observations of the Earth's electric field or auroral precipitation, and that the existing climatological models of the neutral wind are thus sharply limited in theirresolution. The observational data base of thermospheric winds is not sufficient to adequately constrain a three‐dimensional model across a variety of conditions such as solar cycle, season, geomagnetic activity, and so on. Using the physics‐based Time Dependent Ionospheric Model (TDIM) of Utah State University, we look for a quantitative answer to this question: How severe is the limitation imposed on ionospheric models by an uncertain specification of the neutral wind? We find that ionospheric modeling depends upon a detailed specification of the neutral wind to the extent that, if a climatologically averaged wind model is being used as a driver, this will lead to unavoidable uncertainties of 20‐30% in the modeled F‐region densities or Total Electron Content (TEC).

Sources of uncertainty in ionospheric modeling: The neutral wind

AbstractThe neutral wind is a critical input parameter for physics‐based ionospheric models, affecting both the height of the F layer and the total electron content. Unfortunately, the currently available models of the thermospheric wind do not seem to represent it very accurately, and this places a serious limitation on the effectiveness of ionospheric modeling and forecasting. We make use of several decades' worth of midlatitude ionosonde observations of the F region peak, in order to compare the effectiveness of several neutral wind models when used as drivers for an ionospheric model. We check the simulation results against the ground truth of the ionosonde observations using the technique of forecast skill scores. We find that with the ionospheric model in use here (the Utah State University Time Dependent Ionospheric Model (TDIM)), a very simple neutral wind pattern outperforms the more complex models. Increases in skill scores as high as 50% are obtained, relative to the reference case of zero wind; also, in some cases, there are similarly large decreases in skill scores. We view this as a sensitivity study, rather than an effort to identify the best wind model in an absolute sense, because any ionospheric model is an assemblage of algorithms, boundary conditions, and drivers that are themselves imperfect. We identify reasons for the large variability in skill scores with respect to season, longitude, and solar cycle level. We close with a brief discussion of other parameters in ionospheric modeling that are similarly uncertain, e.g., a downward electron flux and the Burnside factor.

Ionospheric model‐observation comparisons: E layer at Arecibo Incorporation of SDO‐EVE solar irradiances

AbstractThis study evaluates how the new irradiance observations from the NASA Solar Dynamics Observatory (SDO) Extreme Ultraviolet Variability Experiment (EVE) can, with its high spectral resolution and 10 s cadence, improve the modeling of the E region. To demonstrate this a campaign combining EVE observations with that of the NSF Arecibo incoherent scatter radar (ISR) was conducted. The ISR provides E region electron density observations with high‐altitude resolution, 300 m, and absolute densities using the plasma line technique. Two independent ionospheric models were used, the Utah State University Time‐Dependent Ionospheric Model (TDIM) and Space Environment Corporation's Data‐Driven D Region (DDDR) model. Each used the same EVE irradiance spectrum binned at 1 nm resolution from 0.1 to 106 nm. At the E region peak the modeled TDIM density is 20% lower and that of the DDDR is 6% higher than observed. These differences could correspond to a 36% lower (TDIM) and 12% higher (DDDR) production rate if the differences were entirely attributed to the solar irradiance source. The detailed profile shapes that included the E region altitude and that of the valley region were only qualitatively similar to observations. Differences on the order of a neutral‐scale height were present. Neither model captured a distinct dawn to dusk tilt in the E region peak altitude. A model sensitivity study demonstrated how future improved spectral resolution of the 0.1 to 7 nm irradiance could account for some of these model shortcomings although other relevant processes are also poorly modeled.

Benefit of the NeQuick Galileo Version in GNSS Single-Point Positioning

The GNSS measurements are strongly affected by ionospheric effects, due to the signal propagation through ionosphere; these effects could severely degrade the position; hence, a model to limit or remove the ionospheric error is necessary. The use of several techniques (DGPS, SBAS, and GBAS) reduces the ionospheric effect, but implies the use of expensive devices and/or complex architectures necessary to meet strong requirements in terms of accuracy and reliability for safety critical application. The cheapest and most widespread GNSS devices are single frequency stand-alone receivers able to partially correct this kind of error using suitable models. These algorithms compute the ionospheric delay starting from ionospheric model, which uses parameters broadcast within the navigation messages. NeQuick is a three-dimensional and time-dependent ionospheric model adopted by Galileo, the European GNSS, and developed by International Centre for Theoretical Physics (ICTP) together with Institute for Geophysics, Astrophysics, and Meteorology of the University of Graz. The aim of this paper is the performance assessment in single point positioning of the NeQuick Galileo version provided by ESA and the comparison with respect to the Klobuchar model used for GPS; the analysis is performed in position domain and the errors are examined in terms of RMS and maximum error for the horizontal and vertical components. A deep analysis is also provided for the application of the exanimated model in the first possible Galileo only position fix.

Central Venous Catheter Insertion by Registered Professional Nurses in the United States: Scope of Practice, Education, Training, and Credentialing Considerations

The USU time-dependent ionospheric model (TDIM) simulated the northern (winter) and southern (summer) ionospheres as they responded to the changing solar wind and geomagnetic activity on 14 January 1988. This period began with moderately disturbed conditions, but as the IMF turned northward, the geomagnetic activity decreased. By 1400 UT, the IMF By component became strongly negative with Bz near zero; and eventually Bz turned southward. This began a period of intense activity as a magnetic storm developed. The magnetospheric electric field and auroral electron precipitation drivers for these simulations were obtained from the Naval Research Laboratories (NRL) Magnetohydrodynamic (MHD) magnetospheric simulation for this event.The F-region ionospheric simulations contrast the summer–winter hemispheres. Then, the difference in how the two hemispheres respond to the geomagnetic storm is related to the differences in magnetospheric energy deposition in the two hemispheres. This also emphasizes the role played by the E-region in the magnetosphere–ionosphere (M–I) coupling and subsequent lack of conjugacy in the two hemispheres. The F-region’s response to the changing geomagnetic conditions also demonstrates a striking lack of conjugacy. This manifests itself in a well-defined ionospheric morphology in the summer hemisphere and a highly irregular morphology in the winter hemisphere. These differences are found to be associated with the differences in the magnetospheric electric field input.

Dayside midlatitude ionospheric response to storm time electric fields: A case study for 7 September 2002

[1] With the storm of 7–8 September 2002 as a study case, we demonstrate that an ionospheric model driven by a suitable storm time convection electric field can reproduce the F region dayside density enhancements associated with the ionospheric storm positive phase. The ionospheric model in this case is the Utah State University Time Dependent Ionospheric Model (TDIM); the electric field model is the University of Michigan's Hot Electron and Ion Drift Integrator (HEIDI). Extensive ground truth is available throughout the study period from two independent sources: ground-based vertical TEC and ionosonde stations; our simulation results are in good agreement with these observations. We address the question of what is the source of the high-density plasma that is seen during the positive storm phase and show that in this case a magnetospheric electric field with an eastward component that penetrates to midlatitudes increases local production on the dayside to a degree that is sufficient to account for the storm time density increases that have been observed.

Storm time density enhancements in the middle‐latitude dayside ionosphere

Enhancements of the total electron content (TEC) in the middle‐latitude dayside ionosphere have often been observed during geomagnetic storms. The enhancements can be as large as a factor of 2 or more, and many sightings of such structures have occurred over the United States. Here we investigate the effectiveness of an expanded convection electric field as a mechanism for producing such ionospheric enhancements. As a test case, we examine the storm period of 5–7 November 2001, for which observations from the DMSP F13 are used to drive the Time Dependent Ionospheric Model (TDIM). Our findings indicate that at favorable universal times, the presence of the expanded electric field is sufficient to create dayside TEC enhancements of a factor of 2 or more. The modeled enhancements consist of locally produced plasma; we do not find it necessary to transport high‐density plasma northward from low latitudes.

A new version of the NeQuick ionosphere electron density model

NeQuick is a three-dimensional and time dependent ionospheric electron density model developed at the Aeronomy and Radiopropagation Laboratory of the Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy and at the Institute for Geophysics, Astrophysics and Meteorology of the University of Graz, Austria. It is a quick-run model particularly tailored for trans-ionospheric applications that allows one to calculate the electron concentration at any given location in the ionosphere and thus the total electron content (TEC) along any ground-to-satellite ray-path by means of numerical integration. Taking advantage of the increasing amount of available data, the model formulation is continuously updated to improve NeQuick capabilities to provide representations of the ionosphere at global scales. Recently, major changes have been introduced in the model topside formulation and important modifications have also been introduced in the bottomside description. In addition, specific revisions have been applied to the computer package associated to NeQuick in order to improve its computational efficiency. It has therefore been considered appropriate to finalize all the model developments in a new version of the NeQuick. In the present work the main features of NeQuick 2 are illustrated and some results related to validation tests are reported.

Anomalous F region response to moderate solar flares

Ionograms recorded with a dynasonde at Bear Lake Observatory, Utah, during moderate solar x‐ray flares exhibit characteristic enhancements to the E and F1 region ionosphere. However, during these same flares, the peak electron density of the ionosphere (NmF2) unexpectedly decreases, recovering after the flare ends. In order to reconcile this anomalous behavior with expected increases to the total electron content (TEC), we undertake a modeling effort using the Time‐Dependent Ionospheric Model (TDIM) developed at Utah State University. For solar input, a simple flare time irradiance model is created, using measurements from the Solar EUV Experiment instrument on the TIMED spacecraft. TDIM simulations show that the anomalous NmF2 response can be explained by assuming a rapid electron temperature increase, which increases the O+ scale height, moving plasma to higher altitudes. The model results are able to reproduce both the decreasing NmF2 as well as the expected TEC enhancement.

Recent developments in ionosphere–thermosphere modeling with an emphasis on solar-variability

The Utah State University modeling developments have led to new results in several areas of ionospheric research. This review will present the most recent of these results and their synergisms with both ground-based and satellite-based observations. Particular attention is given to new results associated with solar variability, a central theme to the TIGER program. The effect on the ionosphere of differences in solar X-EUV spectra will be demonstrated by studies using the time-dependent ionospheric model, while their effect on the coupled thermosphere–ionosphere system will be shown using a new model, the global average ionosphere thermosphere model. How the dayside solar-produced plasma contributes to sub auroral polarization streams, storm enhanced densities, tongues of ionization, plasma patches, polar wind jets, and polar cap scintillations, will be described via recent modeling results from a variety of coupled or driven thermosphere, ionosphere, and magnetosphere models. The review will indicate the need for improved solar output specification, whether via observations or models. These improvements need to be over the flare through solar cycle time scale, with particular attention to the short wavelength end of the spectrum.

Polar F-layer model-observation comparisons: a neutral wind surprise

Abstract. The existence of a month-long continuous database of incoherent scatter radar observations of the ionosphere from the EISCAT Savlbard Radar (ESR) at Longyearbyen, Norway, provides an unprecedented opportunity for model/data comparisons. Physics-based ionospheric models, such as the Utah State University Time Dependent Ionospheric Model (TDIM), are usually only compared with observations over restricted one or two day events or against climatological averages. In this study, using the ESR observations, the daily weather, day-to-day variability, and month-long climatology can be simultaneously addressed to identify modeling shortcomings and successes. Since for this study the TDIM is driven by climatological representations of the magnetospheric convection, auroral oval, neutral atmosphere, and neutral winds, whose inputs are solar and geomagnetic indices, it is not surprising that the daily weather cannot be reproduced. What is unexpected is that the horizontal neutral wind has come to the forefront as a decisive model input parameter in matching the diurnal morphology of density structuring seen in the observations.

A modeling study of the F-region response to SAPS

Sub-auroral polarization stream (SAPS) is the name given to an enhanced westward plasma flow in the night-time mid-latitude ionosphere during geomagnetically disturbed conditions. A description of the SAPS electric field, based on observations from the Millstone Hill incoherent scatter radar, is used here to create a driver for the Utah State University time-dependent ionospheric model in order to assess the effect of the SAPS on the mid-latitude night-time F-region. Tests are conducted for various effective durations of the SAPS, up to 7 h , as well as for different background convection patterns. A longitudinal, or UT, dependence of the ionospheric response is examined. It is found that within the SAPS region, much density structuring occurs, including both enhancements and depletions; in some cases the difference in N m F 2 is as large as a factor of 10.

A mid-latitude space weather hazard driven directly by the magnetosphere

This study revisits and attempts to quantify the effects of high-latitude electric field penetration on the mid-latitude ionosphere. These penetration electric fields (PEFs) are strongest during geomagnetically dynamic and disturbed conditions. The consequences of PEFs arise principally from the induced vertical drift of the F-layer from the eastward electric field component. Both positive and negative storm phases are associated with the PEF. Although no readily available description of the PEF exists, observational and modeling results are combined to provide a crude model. The largest uncertainty arises from a lack of knowledge of whether PEFs are always short lived (less than 1 h ) or are a persisting feature of disturbed conditions. According to simulations with the Utah State University time dependent ionospheric model (TDIM), under K p=3 conditions the PEF readily generates a factor of 2 increase in the pre-midnight ionosphere F-layer density (positive storm phase). For K p=5 conditions this positive phase is further enhanced to produce almost an order of magnitude increase in F-region density. Negative storm phases, F-layer density decreases, are also present in the pre-dawn and pre-noon sectors. The pre-dawn negative storm phase can reach a factor of 10 for K p=5 conditions while the pre-noon depletions are a few 10s of percent. These large density changes have operational impact on systems using coordinate registration based upon Global Positioning Satellite (GPS) measurements. GPS satellite-to-ground radio paths pass through the ionosphere at different angles relative to the zenith and hence have different propagation corrections dependent upon the paths total ionospheric electron content. Factors of 2 change in electron density corresponds to tens of centimeters to meters correction errors in coordinate registration position finding. Corrections this large are a potentially insurmountable obstacle for the GPS based wide area augmentation system (WAAS) designed to provide the airline industry over the USA position accuracy of only a few centimeters. Examples of mid-latitude ray tracing at 5 and 9 MHz are used to demonstrate the frequency sensitivity and coordinate registration dependence upon these factors of 2 ionospheric density changes. Operational systems such as the over-the-horizon (OTH) radar is very sensitive to such dependences and hence upon the mid-latitude PEF.

A theoretical model study of F-region response to high latitude neutral wind upwelling events

Neutral wind upwelling events are well documented in both the northern and southern high latitude ionosphere. The vertical winds in the F-region frequently exceed 100 m/ s , and winds in excess of 200 m/ s have been observed. These upwelling events occur in a latitudinal band of 4°–6° width that extends in local time in the midnight-morning sector; this band always lies poleward of the auroral precipitation. Using the time dependent ionospheric model (TDIM), a series of sensitivity simulations are carried out, based on observational constraints provided by the spectacular upwelling event seen at both the Mawson and Davis stations in the Antarctic on 08 June 1997 (Innis et al., 1999). The model simulations indicate that the F-layer density at any given point may either increase or decrease during an upwelling event, depending upon the past history of the plasma flux tube. Because this past history of the F-layer convection is unknown for the specific upwelling events a detailed case study cannot be undertaken. Instead a series of sensitivity simulations based upon a range of possible convection histories will be studied to determine the relative effect of the upwelling. The absolute density is not dependent upon solar EUV production because of winter conditions, but is sensitive to the auroral electron precipitation. The best F-layer indicator of the upwelling is the height of the layer, h m F 2. For upwelling events with vertical drifts of 100 m/ s h mF 2 can be increased by 100 km in 10 min . Upon leaving an upwelling region, the h m F 2 almost as rapidly decreases to its normal height. Resulting from this lifting of the O + layer is the reduction in O + recombination and 630-nm emission; this latter consequence is observed as a standard feature of the upwelling events. In the topside ionosphere the electron density is responsive to the upwelling. The total electron content (TEC) is not, in general, sensitive to the uplifting events, however, low elevation slant path GPS TEC measurements might well detect the rapid uplifting of the F-layer. The upwelling event observations are insufficient to constrain our understanding of their impact upon the ionosphere. This model study does imply that upwelling events can modify the F-layer height severely. Such layer height modification can have measurable effects on radio frequency ray paths through the ionosphere. To quantify such effects a fuller description of the upwelling events as well as the past history of ionospheric plasma is needed. Experiments with higher time resolution of both the neutral parameters and F-region at multiple locations are necessary to unravel these complex events.

Driving the high-latitude ionosphere with variable time resolution “ K-like” geomagnetic indices

The 3-h K p index is widely used as a measure of geomagnetic activity for ionospheric studies. Specifically, it is the planetary index used to determine the geomagnetic dependence of statistical auroral patterns and the convection electric field for certain models. Its quasi anti-logarithm, the A p index, is similarly used in statistical models of the neutral atmosphere and neutral wind. Physics-based ionospheric models, such as the Utah State University (USU) Time-Dependent Ionospheric Model (TDIM), use these statistical models as magnetospheric and thermospheric inputs. However, the 3-h time interval between index computations is now considered a shortfall with regard to specifying and forecasting phenomena known to have faster time constants, e.g., auroral electrojet variations during a substorm. Therefore, these indices have been targeted for high-time resolution development; we have developed such indices in Della-Rose et al. (1999). We now use our 15-minute station “ K-like” index to determine the effect of introducing high-time resolution magnetic fluctuations into the TDIM inputs. This study represented the high-latitude ionosphere by a grid of 1484 locations, and was carried out for a geomagnetic storm period during solar maximum and “simulated” winter solstice conditions. We found that, for fixed Interplanetary Magnetic Field (IMF) B y / B z ratio, driving the TDIM with our 15-minute “ K-like” index altered the average high-latitude N m F 2 value by as much as 8% (vs. the average N m F 2 obtained using a 3-h index to drive the TDIM). More significantly, the standard deviation of the N m F 2 variations was up to 35%. Under some conditions, the average N m F 2 was changed by up to 30% with a standard deviation of over 60%. However, the effect of selecting different convection patterns that represented three southward IMF B z orientations led to larger effects. The high-latitude average N m F 2 changed by 10% or less, but the spread in the distribution always ranged from standard deviations of 29 to 68%. These results indicate that there is a substantial need to consider both short-term magnetic fluctuations and inclusion of real-time IMF data in the inputs to ionospheric models.

Interhemispheric comparison of TDIM E- and F-region ionospheres on 14 January 1988

The USU time-dependent ionospheric model (TDIM) simulated the northern (winter) and southern (summer) ionospheres as they responded to the changing solar wind and geomagnetic activity on 14 January 1988. This period began with moderately disturbed conditions, but as the IMF turned northward, the geomagnetic activity decreased. By 1400 UT, the IMF B y component became strongly negative with B z near zero; and eventually B z turned southward. This began a period of intense activity as a magnetic storm developed. The magnetospheric electric field and auroral electron precipitation drivers for these simulations were obtained from the Naval Research Laboratories (NRL) Magnetohydrodynamic (MHD) magnetospheric simulation for this event. The F-region ionospheric simulations contrast the summer–winter hemispheres. Then, the difference in how the two hemispheres respond to the geomagnetic storm is related to the differences in magnetospheric energy deposition in the two hemispheres. This also emphasizes the role played by the E-region in the magnetosphere–ionosphere (M–I) coupling and subsequent lack of conjugacy in the two hemispheres. The F-region’s response to the changing geomagnetic conditions also demonstrates a striking lack of conjugacy. This manifests itself in a well-defined ionospheric morphology in the summer hemisphere and a highly irregular morphology in the winter hemisphere. These differences are found to be associated with the differences in the magnetospheric electric field input.

Gradient drift instability growth rates from global‐scale modeling of the polar ionosphere

The winter polar ionosphere, under southward interplanetary magnetic field (IMF) conditions, experiences irregularity development leading to consequences such as scintillation on transionospheric communication links. These irregularities are associated with antisunward convecting polar ionospheric patches. The gradient drift instability (GDI) has been considered a primary candidate for the generation of these irregularities, or at least the long‐wavelength energy source of the irregularity‐wave cascade process. The Utah State University time‐dependent ionospheric model (TDIM) enables the polar cap ionosphere and its patches to be modeled on a large scale in a time‐evolving manner. Hence, at each point in space and time, the TDIM has adequate information to compute the growth rate of the gradient drift instability. The spatial gradients are based on a 92×92 km TDIM grid resolution, while the time resolution can be as short as 30 s. In this study, we present results of the GDI linear growth rate calculations for the F region. For a first time, snapshots of the instantaneous GDI linear growth rates over the polar ionosphere are shown. These show, in part, the correlation of the GDI with polar cap patches. Then we present the time evolution of the linear growth rate as plasma flux tubes convect. It is shown that a flux tube of plasma can, in fact, change between being unstable and stable to the GDI as the plasma convection pattern switches in response to changing IMF conditions. These convective results are essential information if an assessment of whether or not a plasma flux tube is stable to the gradient drift mechanism is to be made.

Comparison of measured high latitude F-region ion composition climatological variability with models

Satellite measurements of the global F-region ion composition morphology, due to orbit-to-orbit variations in space and time, are most effectively examined statistically, taking into consideration the ranges of variability in the data. Simple averages of the measurements do not clearly delineate narrow and time varying features such as density troughs/holes, sharp ionospheric layers, or even auroral region enhancements of electron temperature/molecular ion concentrations. These in fact are the most prominent features seen along individual satellite passes and are features which have prominent climatological variations To explore how well current ionosphere models fare with reality at middle and high latitudes, the entire ensemble of available solar minimum satellite ion composition measurements (predominantly from Atmosphere Explorer C and D) are sorted into spatial, temporal and magnetic/solar activity indices bins. Ion concentrations obtained from multiple runs of the International Reference Ionosphere (IRI) and the Utah State University Time Dependent Ionosphere model (TDIM), sorted into bins similar to those used for the satellite data sets are compared to the measurements. As currently configured the IRI model does not make a good match with the middle and high latitude topside ionosphere ion composition measurements. The TDIM is a better match to the measurements but does not reproduce the deepest high latitude ionospheric troughs and auroral-cusp molecular ion enhancements.

Effects of thermospheric gravity waves on the polar ionosphere

One of the results of the European, United States, and Japanese efforts to establish extensive polar cap observational facilities will be the generation of simultaneous and complementary two-dimensional ionosphere and thermosphere data bases. In anticipation of these extensive data sets, this paper considers the coupling between the thermosphere and ionosphere in the polar region from a theoretical point of view, aided by the USU Time Dependent Ionospheric Model (TDIM). To date, we have used statistical climatology thermospheric drivers; these being the Hedin neutral atmosphere (MSIS) and neutral wind models (Hedin et al., 1991). These inputs do not contain gravity waves. The question of prime interest in this paper is: What will a gravity wave do to the high-latitude ionosphere and can these new data sets capture enough of the two-dimensional time evolution of the phenomenon to unambiguously identify the perturbations? Our modeling results indicate that an antisunward propagating gravity wave with a phase velocity that is the same as the plasma convection velocity will experience a constant vertical force from the thermosphere, which amplifies the effect of the gravity wave.