Bottomside Electron Density Profiles Research Articles

A storm-time global electron density reconstruction model in three-dimensions based on artificial neural networks

We present results of a dedicated global storm-time model for the reconstruction of ionospheric electron density in three-dimensions. Using the storm criterion of |Dst|⩾50 nT and Kp⩾4, the model is constructed using a combination of radio occultation and ionosonde data during the periods of 2006–2021 and 2000–2020, respectively. From the ionosonde data, only the bottomside electron density profiles up to the maximum height of the F2 layer (hmF2) are considered. In addition to the selection of storm-time data only for the model development, we have investigated the inclusion of time history for the geomagnetic storm indicator Kp at 9 and 33 h in an attempt to take into account the delay of physical processes related to atmospheric gravity waves or traveling ionospheric disturbances and thermospheric composition changes which drive varying ionospheric storm effects during storm conditions. Based on incoherent scatter radar data and in comparison with the IRI 2020 model, the developed storm-time model provides foF2 modelling improvement of above 50% during the storm main phase over Millstone Hill (42.6°N, 71.5°W) and Tromsø (69.6°N, 19.2°E) for the storm periods of 3–6 November 2021 and 23–25 March 2023, respectively. Modelled results for Jicamarca (11.8°S, 77.2°W) show that the storm-time model estimates foF2 by an improvement of over 20% during the main phase of the 07–10 September 2017 storm period. As the ionospheric conditions return to quiet time levels, the IRI 2020 model perform better than the constructed storm -time model

Construction and Application of Global Middle- and Low-Latitude Bottomside Electron Density Profile Model Based on Multisource Satellite Geodetic Data and International Reference Ionosphere Model

Construction and Application of Global Middle- and Low-Latitude Bottomside Electron Density Profile Model Based on Multisource Satellite Geodetic Data and International Reference Ionosphere Model

A Regional Model of Topside Ionospheric Effective Scale Heights Derived From Ionosonde and GNSS TEC

AbstractIonospheric scale height is critical for the structure of electron density profile in the ionosphere. However, mostly, the effective scale heights (fitted with mathematical functions) instead of topside ionospheric scale heights were used to reconstruct the topside profile. In this study, a new method was proposed to estimate topside ionospheric effective scale heights from ionosonde and Global Navigation Satellite System (GNSS) vertical total electron content (TEC). First, the bottomside electron density profile can be estimated from ionograms. Then, combined the parameters of the F2 layer and effective scale heights, topside electron density profile can be estimated by Epstein Layer. Furthermore, ionosonde TEC can be compared with GNSS vertical TEC by adjusting effective scale heights to obtain best‐fit ionosonde TEC and effective scale heights. In this study, ionosonde and GNSS TEC data recorded at Zhangye station (39.40°N, 100.13°E) were used to test the performance. Results show that diurnal and seasonal characteristics of effective scale heights are consistent with previous studies. Furthermore, the Empirical Orthogonal Function technique was used to build a regional and empirical model of effective scale heights. Results show that the accuracy (between ±2.5 TECU) of ionosonde TEC are about 91.26% by comparing with GNSS TEC. Considered that the traditional methods mostly underestimated TEC, it indicates that the accuracy of ionosonde TEC can be improved significantly by the new model of effective scale heights. Furthermore, results show that the topside electron densities estimated by the proposed method are comparable with in situ observations measured by Swarm B.

Comparison of bottomside ionospheric profile parameters (B0 and B1) extracted from FORMOSAT-7/COSMIC-2 GNSS Radio occultations with Digisondes and IRI-2016 model

The bottomside thickness (B0) and shape (B1) are two important parameters considered in the bottomside electron density profile (EDP) specification of the International Reference Ionosphere (IRI) model that is the most widely accepted global empirical ionospheric model. In the present study, we investigated B0 and B1 as derived from least-square fitting of FORMOSAT-7/COSMIC-2 (F7/C2) radio occultation (RO) profiles by employing certain quality constraints in accordance to coincident Digisonde soundings. We performed a comparative analysis of the local time diurnal, seasonal and latitudinal behaviour of B0 and B1 parameters from a huge database of F7/C2 profiles accumulated during the last two years (2020 and 2021) with estimations from the IRI-2016 submodels: Bil-2000, Gul-1987, and ABT-2009, referring to the bottomside profile characteristics during the low solar activity period of 25th solar cycle. The results reveal daytime underestimation and nighttime overestimation features of IRI submodels. The typical pre-sunrise enhancement in B0 is clearly discernible in the F7/C2 observations which could not be reproduced in any of the IRI submodels. Moreover, the equatorial bottomside thickness anomaly (EBTA) presenting hemispheric asymmetry is not evidenced in the observed as well as modelled parameters. The sharp changeover in B0 magnitude from summer to winter solstice hemisphere and spring to fall equinox hemisphere in Gul-1987 indicates its inability to accurately represent the B0 variation at the equatorial and low latitude sector. Despite the fact that ABT-2009 performs relatively better than Gul-1987 sub-model based on F7/C2 and Digisonde datasets in different seasons, we demonstrate that there is room for possible improvement in terms of B0 and B1 representation.

Adaptation of the bottomside electron density profile of the IRI model to data of topside radiosounding

A method is proposed for reconstructing the electron density profiles N(h) of the IRI model from ionograms of topside satellite sounding of the ionosphere. An ionograms feature is the presence of traces of signal reflection from the Earth's surface. The profile reconstruction is carried out in two stages. At the first stage, the N(h) –profile is calculated from the lower boundary of the ionosphere to the satellite height (total profile) by the method presented in this paper using the ionogram. In this case, the monotonic profile of the topside ionosphere is calculated by the classical method. The profile of the inner ionosphere is represented by analytical functions, the parameters of which are calculated by optimization methods using traces of signal reflection, both from the topside ionosphere and from the Earth. At the second stage, the profile calculated from the ionogram is used to obtain the key parameters: the height of the maximum hmF2 of the F2 layer, the critical frequency foF2, the values of B0 and B1, which determine the profile shape in the F region in the IRI model. The input of key parameters, time of observation, and coordinates of sounding into the IRI model allows obtaining the IRI-profile corrected to real experimental conditions. The results of using the data of the ISIS-2 satellite show that the profiles calculated from the ionograms and the IRI profiles corrected from them are close to each other in the inner ionosphere and can differ significantly in the topside ionosphere. This indicates the possibility of obtaining a profile in the inner ionosphere close to the real distribution, which can significantly expand the information database useful for the IRTAM (IRI Realmax Assimilative Modeling) model. The calculated profiles can be used independently for local ionospheric research.

A Bottomside Parameterization for the Empirical Canadian High Arctic Ionospheric Model

AbstractIn this study, we present a bottomside model representation to be used by the Empirical Canadian High Arctic Ionospheric Model (E‐CHAIM). This model features a new approach to modeling the bottomside electron density; namely, instead of modelling electron density directly, E‐CHAIM models the altitude profile of the scale thickness of a single bottomside layer. In this approach, the curvature in the bottomside associated with the E region and F1 layer is represented in the scale thickness domain as a peak function centered at the layer peak altitude. The use of this approach ensures the production of explicitly doubly differentiable bottomside electron density profiles and directly avoids issues known to exist within current standards, such as the International Reference Ionosphere (IRI), which has discontinuities in space, time, and in the vertical electron density gradient. In terms of performance, after removing the impacts of hmF2 and NmF2, the new E‐CHAIM profile function generally performs comparably to the IRI, with bottomside TEC from both models within 2.0 TECU (1 TECU = 1016 e/m3) of observations. More specifically, the E‐CHAIM bottomside is demonstrated to outperform the IRI bottomside function in the F region during low solar activity periods with respect to incoherent scatter radar observations. At high latitudes, E‐CHAIM tends to outperform the IRI during winter months by between 10% and 40% of NmF2 while being outperformed by the IRI by between 10% and 25% of NmF2 during summer periods, mainly during the daytime at high solar activity.

Response of Ionospheric Profile Parameters to Equatorial Electrojet Over Peruvian Station

AbstractThe response of the ionospheric bottomside electron density profile parameters of the F2 layer, namely, the maximum electron density (NmF2), the maximum height of F2 layer (hmF2), and bottomside thickness (B0) parameter to the equatorial electrojet (EEJ) current is examined for a Peruvian location at the Jicamarca station (12 °S, 76.9 °W) in the South American sector. The results of the analysis show that both hmF2 and B0 increase for ~2 h before sunrise and exhibit a postsunset peak during the equinoctial and summer months. The increase in the peak height, hmF2, is observed to terminate before midday, while B0 continued to increase throughout the daytime. The apparent midday and postnoon peaks in NmF2 occur in all the seasons under study. It was demonstrated that a relationship exists between EEJ and the profile parameters hmF2 and B0 during low and moderate solar conditions. Conversely, the correlation coefficient between EEJ and NmF2 is statistically significant only during solar minimum conditions but correlates poorly, if at all, with EEJ during moderate solar activity.

A Data Assimilated Regional Ionosphere Model Using the Total Electron Content from the Korean GPS Network

In this study, we develop a time-dependent three-dimensional regional ionosphere model over the Korean peninsula (32° N - 42° N, 122° E - 132° E, and 100 - 1000 km in altitude) by using data assimilation technique. Slant total electron content (STEC) data from 80 global positioning system (GPS) receiver stations on the Korean peninsula are assimilated into International Reference Ionosphere (IRI) 2016 as a background model. The assimilated results are validated with independent sources of electron density information: 1) GPS STEC not used in the assimilation and 2) f o F2 and bottom side electron density profiles from two ionosondes. Results show that data assimilation estimates the observations with a 3 - 41% improvement over the climatic IRI 2016 model.

Bottom side profiles for two close stations at the southern crest of the EIA: Differences and comparison with IRI-2012 and NeQuick2 for low and high solar activity

Bottom side electron density profiles for two stations at the southern crest of the Equatorial Ionization Anomaly (EIA), São José dos Campos (23.1°S, 314.5°E, dip latitude 19.8°S; Brazil) and Tucumán (26.9°S, 294.6°E, dip latitude 14.0°S; Argentina), located at similar latitude and separated by only 20° in longitude, have been compared during equinoctial, winter and summer months under low (year 2008, minimum of the solar cycle 23/24) and high solar activity (years 2013–2014, maximum of the solar cycle 24) conditions. An analysis of parameters describing the bottom side part of the electron density profile, namely the peak electron density NmF2, the height hmF2 at which it is reached, the thickness parameter B0 and the shape parameter B1, is carried out. Further, a comparison of bottom side profiles and F-layer parameters with the corresponding outputs of IRI-2012 and NeQuick2 models is also reported. The variations of NmF2 at both stations reveal the absence of semi-annual anomaly for low solar activity (LSA), evidencing the anomalous activity of the last solar minimum, while those related to hmF2 show an uplift of the ionosphere for high solar activity (HSA). As expected, the EIA is particularly visible at both stations during equinox for HSA, when its strength is at maximum in the South American sector. Despite the similar latitude of the two stations upon the southern crest of the EIA, the anomaly effect is more pronounced at Tucumán than at São José dos Campos. The differences encountered between these very close stations suggest that in this sector relevant longitudinal-dependent variations could occur, with the longitudinal gradient of the Equatorial Electrojet that plays a key role to explain such differences together with the 5.8° separation in dip latitude between the two ionosondes. Furthermore at Tucumán, the daily peak value of NmF2 around 21:00 LT during equinox for HSA is in temporal coincidence with an impulsive enhancement of hmF2, showing a kind of “elastic rebound” under the action of the EIA. IRI-2012 and NeQuick2 bottom side profiles show significant deviations from ionosonde observations. In particular, both models provide a clear underestimation of the EIA strength at both stations, with more pronounced differences for Tucumán. Large discrepancies are obtained for the parameter hmF2 for HSA during daytime at São José dos Campos, where clear underestimations made by both models are observed. The shape parameter B0 is quite well described by the IRI-2012 model, with very good agreement in particular during equinox for both stations for both LSA and HSA. On the contrary, the two models show poor agreements with ionosonde data concerning the shape parameter B1.

Regional 3‐D ionospheric electron density specification on the basis of data assimilation of ground‐based GNSS and radio occultation data

AbstractIn this paper, a regional 3‐D ionospheric electron density specification over China and adjacent areas (70°E–140°E in longitude, 15°N–55°N in latitude, and 100–900 km in altitude) is developed on the basis of data assimilation technique. The International Reference Ionosphere (IRI) is used as a background model, and a three‐dimensional variational technique is used to assimilate both the ground‐based Global Navigation Satellite System (GNSS) observations from the Crustal Movement Observation Network of China (CMONOC) and International GNSS Service (IGS) and the ionospheric radio occultation (RO) data from FORMOSAT‐3/COSMIC (F3/C) satellites. The regional 3‐D gridded ionospheric electron densities can be generated with temporal resolution of 5 min in universal time, horizontal resolution of 2° × 2° in latitude and longitude, and vertical resolution of 20 km between 100 and 500 km and 50 km between 500 and 900 km. The data assimilation results are validated through extensive comparison with several sources of electron density information, including (1) ionospheric total electron content (TEC); (2) Abel‐retrieved F3/C electron density profiles (EDPs); (3) ionosonde foF2 and bottomside EDPs; and (4) the Utah State University Global Assimilation of Ionospheric Measurements (USU‐GAIM) under both geomagnetic quiet and disturbed conditions. The validation results show that the data assimilation procedure pushes the climatological IRI model toward the observation, and a general accuracy improvement of 15–30% can be expected. Thecomparisons also indicate that the data assimilation results are more close to the Center for Orbit Determination of Europe (CODE) TEC and Madrigal TEC products than USU‐GAIM. These initial results might demonstrate the effectiveness of the data assimilation technique in improving specification of local ionospheric morphology.

F region electron density profile inversion from backscatter ionogram based on international reference ionosphere

Ionospheric backscatter sounding transmits HF (3–30MHz) radio wave obliquely into ionosphere and receives echoes backscattered from remote ground. Due to the focusing effect, the echoes form leading edge on the swept frequency backscatter ionogram (BSI). This kind of backscatter ionogram contains plentiful ionospheric information, such as electron density, radio wave propagation modes and maximum usage frequency (MUF). By inversion algorithm, the backscatter ionogram can provide two-dimensional electron density profile (EDP) down range. In this paper, we propose an ionospheric F2 region EDP inversion algorithm. By utilizing the F2 bottomside electron density profile represented by the International Reference Ionosphere (IRI) model and ray tracing techniques, this approach inverts the leading edge of the backscatter ionogram to two dimensional F region EDP. Results of validation experiments demonstrate that the inverted ionospheric EDPs show good agreement with the results of vertical ionosonde and provide reliable information of ionosphere. Thus the proposed inversion algorithm provide an effective and accurate method for achieving large scale and remote ionospheric electron density structure.

Vertical electron density and topside effective scale height (<I>H</I><sub>T</sub>) variations over the Indian equatorial and low latitude stations

Abstract. Understanding the vertical electron density profile, which is the altitudinal variation of ionospheric electron density distribution is an important aspect for the ionospheric investigations. In this paper, the bottom-side electron density profiles derived from ground based ionosonde data and the ROCSAT-1 in-situ electron density data were used to determine the estimates of the topside electron density profiles using α-Chapman function over an equatorial station Trivandrum (8.47° N, 76.91° E) and a low latitude station Waltair (17.7° N, 83.3° E) in the Indian region. The reconstructed electron density profiles are compared with IRI (2007) model derived vertical electron density profiles which resulted in significant deviations between the two different profiles. Both the reconstructed electron density profiles and the IRI model derived profiles are integrated independently to derive the Total Electron Content (TEC) values which are compared with GPS derived TEC values. TEC values derived from the reconstructed electron density profiles give better estimates with the GPS-TEC compared to those of IRI model derived TEC values. Compared to the GPS-TEC, the IRI model is underestimating the TEC values during day-time and is overestimating during night-time at both the stations. The percentage deviations of IRI derived TEC from GPS-TEC are larger compared to those between reconstructed profile derived TEC and GPS-TEC. F2-layer peak electron density, peak height and electron density at ROCSAT altitudes (≈600 km) are used to derive the effective scale heights (HT) of the topside ionosphere during the period from July 2003 to June 2004. The diurnal and seasonal variations of HT and E×B drift velocities are presented in this paper. The diurnal variation of the effective scale height (HT) shows peak values around noon hours with higher values during day-time and lower values during night-time both at Trivandrum and Waltair. The E×B drift velocities at both the places also have shown a clear diurnal variation with a negative peak around 04:00 LT and maximum during day-time hours. The higher and lower values of HT seem to be associated with positive and negative phases of the E×B drift velocities, respectively.

Midday bottomside electron density profiles during moderate solar activity and comparison with IRI-2001

Bottomside electron density (Ne-h) profiles during midday (10–14 h) are analyzed using modern digital ionosonde observations at a low-middle latitude station, New Delhi (28.6N, 77.2E, dip 42.4N), for the period from January 2003 to December 2003, pertaining to moderate solar activity (MSA). Each individual profile is normalized with respect to the peak height and density (hmF2, NmF2) of the F2-region. These profiles are compared with those obtained from the International Reference Ionosphere (IRI-2001) model. Bilitza [Bilitza, D. International Reference Ionosphere 2000. Radio Sci. 36 (2), 261–275, 2001] using both the options namely: Gulyaeva’s model [Gulyaeva, T.L. Progress in ionospheric informatics based on electron density profile analysis of ionograms. Adv. Space Res. 7 (6) 39–48, 1987] and B0 Tab. option [Bilitza, D., Radicella, S.M., Reinisch, B.W., Adeniyi, J.O., Mosert Gonzalez, M.E., Zhang, S.R., Obrou, O. New B0 and B1 models for IRI. Adv. Space Res. 25 (1), 89–95, 2000]. The study reveals that during summer and equinox, the IRI model with B0 Tab. option in general, produces better agreement with the observed median profiles, while the IRI predictions using Gulyaeva’s option, overestimate the electron density distribution at all the heights below the F2-peak. However, during winter, in general, the IRI model, using both the options, reveals shows fairly good agreement with the observations.

Spatial distribution of ionization in the equatorial and low‐latitude ionosphere of the Indian sector and its effect on the pierce point altitude for GPS applications during low solar activity periods

The equatorial and low‐latitude ionosphere is characterized by dynamic changes in the spatial distribution of F region electron density. The in situ density data from Indian SROSS C2 satellite was used in conjunction with the international reference ionosphere (IRI) to demonstrate how the median models have limitations to represent the spatial gradients in the equatorial and subtropical latitudes in the Indian sector. The ground‐based ionosonde data was used to derive the bottomside electron density profiles which were matched with IRI to derive the complete F region electron density profile for different times to show the variability in the centroid of ionization mass distribution due to the equatorial plasma dynamics associated with Appleton ionization anomaly. The study brings out that a uniform ionospheric pierce point altitude cannot be assumed for GPS applications in this sector. However, during low sunspot activity periods, the GPS‐derived total electron content (TEC) using 2 × 2 grid point data indicates that spatial gradients in TEC are not too significant in meridian transects and that the assumption of homogeneous distribution is valid for the conversion of slant to vertical TEC even in the equatorial latitudes during solar minimum. Keeping this in view, a qualitative study has been carried out on the possible variability in ionospheric pierce point altitude at representative subtropical latitude in the Indian sector and the results are discussed in light of diurnal and seasonal features of the equatorial ionosphere.

Configuration of the upper boundary of the ionosphere

Variations of the upper boundary of the ionosphere (UBI) are investigated based on three sources of information: (i) ionosonde-derived parameters: critical frequency foF2, propagation factor M3000F2, and sub-peak thickness of the bottomside electron density profile; (ii) total electron content (TEC) observations from signals of the Global Positioning System (GPS) satellites; (iii) model electron densities of the International Reference Ionosphere (IRI*) extended towards the plasmasphere. The ionospheric slab thickness is calculated as ratio of TEC to the F2 layer peak electron density, NmF2, representing a measure of thickness of electron density profile in the bottomside and topside ionosphere eliminating the plasmaspheric slab thickness of GPS-TEC with the IRI* code. The ratio of slab thickness to the real thickness in the topside ionosphere is deduced making use of a similar ratio in the bottomside ionosphere with a weight Rw. Model weight Rw is represented as a superposition of the base-functions of local time, geomagnetic latitude, solar and magnetic activity. The time-space variations of domain of convergence of the ionosphere and plasmasphere differ from an average value of UBI at ∼1000 km over the earth. Analysis for quiet monthly average conditions and during the storms (September 2002, October–November 2003, November 2004) has shown shrinking UBI altitude at daytime to 400 km. The upper ionosphere height is increased by night with an ‘ionospheric tail’ which expands from 1000 km to more than 2000 km over the earth under quiet and disturbed space weather. These effects are interposed on a trend of increasing UBI height with solar activity when both the critical frequency foF2 and the peak height hmF2 are growing during the solar cycle.

Diurnal and seasonal variation of B0,B1 parameters during high solar activity period at low mid-latitude and their comparisons with IRI-2001 model

Diurnal and seasonal variations of bottom side electron density profile shape parameters B0, B1, representing the bottom side F2-layer thickness and shape, are examined using modern digital ionosonde observations at a low-middle latitude station, New Delhi (28.6 °N, 77.2 °E, dip 42.4 °N) for high solar activity (HSA) (2001–2002). Median values of these parameters are obtained at each hour during different seasons and compared with the predictions of the latest version of the international reference ionosphere (IRI), IRI-2001 model using both the options namely: IRI (Gulyaeva) and IRI (B0 Tab.). Results show in general, a large variability in B0, and B1 parameters during all the seasons, the variability is larger during nighttime than by daytime. The diurnal variation of median B0, in general, show more or less similar trends with diurnal maximum occurring around noontime, except during summer, when it occurs between 09 and 10 LT. Variation pattern of B1 in general, is identical in all the seasons with lower values of B1 by daytime than by night. Comparative studies of B0 with those obtained with the IRI model show that in general, IRI (B0 Tab.) option reveals better agreement with the observations during all the seasons for local times from about 10 LT to about 16 LT, while outside this time period IRI (Gulyaeva) matches well with the observations. The predicted B1 parameter, using IRI (B0 Tab.) is close to observations in terms of diurnal variation, while B1 using IRI (Gulyaeva) option, assumes a fixed value of 3 at all local times irrespective of season.

A study of the ionogram derived effective scale height around the ionospheric <I>hm</I>F2

Abstract. The diurnal, seasonal, and solar activity variations of the ionogram derived scale height around the ionospheric F-layer peak (Hm) are statistically analyzed at Wuhan (114.4° E, 30.6° N) and the yearly variations of Hm are also investigated for Wuhan and 12 other stations where Hm data are available. Hm, as a measure of the slope of the topside electron number density profiles, is calculated from the bottomside electron density profiles derived from vertical sounding ionograms using the UMLCAR SAO-Explorer. Results indicate that the value of median Hm increases with increasing solar flux. Hm is highest in summer and lowest in winter during the daytime, while it exhibits a much smaller seasonal variation at night. A common feature presented at these 13 stations is that Hm undergoes a yearly annual variation with a maximum in summer during the daytime. The annual variation becomes much weaker or disappears from late night to pre-sunrise. In addition, a moderate positive correlation is found between Hm with hmF2 and a strong correlation between the bottomside thickness parameter B0 and Hm. The latter provides a new and convenient way for empirical modeling the topside ionospheric shape only from the established B0 parameter set.

Predicting the ionospheric F layer using neural networks

A new neural network (NN) based ionospheric model for the bottomside electron density profile over Grahamstown, South Africa (33.3°S, 26.5°E) has been developed and is referred to as the LAM model. This paper discusses the development of the F layer contribution to the LAM model. Archived data from the Grahamstown ionospheric station have been presented to various NNs, which have been trained to predict the parameters required to produce an electron density profile. Since the dataset was only made up of Grahamstown data, the model is currently a single station model. The input space designed for the F layer contribution to the LAM model consisted of various combinations of the following parameters: day number (DN), hour (HR), a measure of the solar activity, and a measure of the magnetic activity. The solar activity input was represented by a 2‐month running mean value of the sunspot number (R2), while the magnetic activity variable was represented by either a 24‐hour or 48‐hour running mean of the magnetic ak value (A8 or A16). The outputs from the NNs were the peak parameters and Chebyshev coefficients required to describe the shape and location of the F profile. This paper also discusses how NNs have been employed to provide an effective mechanism for determining the probability of the existence of an F1 layer. An F1 layer can exist in one of the following three states; F1 exists, no F1, or F1 exists in L condition state. A special NN was trained to provide the probability of F1 layer existence in each of these states. An L algorithm is applied to determine the shape and location of the profile under L condition state. In addition, a smoothing technique was designed to deal with discontinuities across the F1‐F2 boundary. It is shown that the NN‐based LAM model can successfully predict descriptions for the shape and location of the average profile for a given input set, and, in addition, that NNs can be employed to provide solutions to previously difficult prediction tasks such as the probability of F1 layer existence.

A statistical study of ionospheric profile parameters derived from Millstone Hill incoherent scatter radar measurements

Diurnal, seasonal, and solar activity variations of the bottomside electron density profile parameters B0 and B1, representing the F2 layer thickness and shape, are studied using a large incoherent scatter radar dataset for Millstone Hill covering the period 1976–2002. These results are compared with the latest IRI model. Our statistical study is characterized by morning and afternoon falls in the diurnal variation of B0 for seasons other than summer and a ∼15% change in B1 over a solar cycle, features not fully well represented by the standard IRI model. The standard IRI B1, however, is very close to observations in terms of the diurnal variation.

Recent approaches to modeling ionospheric weather

The ionosphere is a complex and dynamic medium that exhibits weather features at all latitudes and longitudes. The weather features are driven by internal processes as well as by interplanetary and magnetospheric phenomena. Because ionospheric weather can have a detrimental effect on both ground-based and space-based systems, a large international effort has been devoted to developing both specification and forecast models, with the aim of predicting the occurrence, duration, and intensity of weather features. Currently, the most promising ionospheric weather models are the physics-based data-driven models that use Kalman filter data assimilation techniques. The data assimilation is used both to obtain the inputs needed by the physics-based models and to adjust the model outputs, i.e., the calculated electron density distribution. The data sources used in the physics-based assimilation models include ground-based GPS/TEC data, bottomside electron density profiles obtained from digisondes, in situ DMSP satellite measurements, satellite-to-satellite occultation data, TECs obtained from satellites with radio beacons, and UV data obtained via remote sensing. The status of the modeling will be reviewed.