Electron Density Height Research Articles

Statistical Study of Electron Density Enhancements in the Ionospheric F Region Associated With Pulsating Auroras

AbstractPulsating auroras (PsAs) are considered to be caused by energetic (>a few keV) electron precipitation. Additionally, soft electron precipitation (<a few keV) has often been observed in PsAs. This soft electron precipitation enhances the electron density in the ionospheric F region. However, to date, the relationship between PsAs and soft electron precipitation has not been well understood. In this study, using the data taken by the European incoherent scatter radar and the auroral all‐sky imager at Tromsø, we conducted two case studies to investigate, in detail, the relationship between the electron density height profile and the type of aurora. Additionally, we conducted statistical studies for 14 events to elucidate how often F region electron density enhancement occurs with a PsA. We consequently found that 76% of electron density height profiles showed a local peak in the F region, with electron temperature enhancements. It was also found that 89% of the F region peak altitudes were above the peak altitude of the ionization rate produced by electrons of characteristic energy below 100 eV. The occurrence rate of these profiles in the hourly magnetic local time (MLT) exceeded 80% in the 22–3 MLT sectors. We suggest that the electron density enhancement in the F region would have been caused by electrostatic electron cyclotron harmonic waves in the magnetosphere. Another candidate would have been polar patches that had traveled from the dayside ionosphere.

Reconstruction of Electron-Density Height Profiles Based on Vertical Sounding Data under Multistratification of the E Region

Reconstruction of Electron-Density Height Profiles Based on Vertical Sounding Data under Multistratification of the E Region

Comparison of Low‐Latitude Ionospheric Scintillation Forecasting Techniques Using a Physics‐Based Model

AbstractThe temporal change in height of a specific electron density can be used as a proxy for vertical plasma drift (PVPD) at the magnetic equator. The use of PVPDs as a predictor of low‐latitude ionospheric scintillation during the subsequent evening has previously been shown to have forecasting skill when using ionosonde data. The implementation of this approach using a physics‐based model is proposed to provide greater forecast antecedence without the need for local ionosondes. For the first time, the physics‐based model PVPD method is compared to another forecasting approach that uses a physics‐based model to calculate Rayleigh‐Taylor growth rates (RTGRs). In equinoctial test cases considered, when appropriate scintillation observation thresholds are selected, PVPD forecasting is shown to have skill similar to or better than the RTGR method using the same physics‐based model. PVPD forecasting requires only electron densities and corresponding altitudes. Therefore, this approach could be applied using an ionospheric data assimilation model whereas the majority of these models do not provide output for all variables required for RTGR forecasting. The forecasting skill in these test cases, the simplicity of physics‐based PVPD forecasting, and the suitability of this method for use of ionospheric data assimilation model output make this method attractive as a forecasting tool in an operational setting if skill can be further demonstrated for a wide range of conditions. However, both PVPD and RTGR forecasting skill are shown to be limited during solstitial months with high scintillation activity. This may be improved by using a data assimilation model.

Validating IRI-2016 for quiet-time F2-region peak electron density height (hmF2) at different latitudes during moderate solar activity

• IRI-2016 hmF2 was validated for stations at three different latitudes during moderate solar activity. • All the hmF2 model options (BSE, AMTB, and SHU) show varying strength and weakness. • BSE option could not be jettisoned; thus, the need for a robust ionosonde-derived hmF2 and M(3000)F2 database. The height of the peak electron density (hmF2) is crucial in the study of some ionospheric electrodynamics and for high frequency (HF) radio communication circuit planning. We validated the three hmF2 model options of the 2016 version of the International Reference Ionosphere (IRI) with data from three ionosonde stations, each from different latitudinal ranges. The recent options: Altadill-Magdaleno-Torta-Blanch (AMTB2013) and SHUbin (SHU-2015), seem to be better than the previous one – Bilitza-Sheikh-Eyfrig (BSE-1979), particularly at low- and mid-latitudes. Despite the identified limitations in literature, BSE-1979 seems to be better at some periods and regions, particularly at the mid-latitude and high latitude in the nighttime. The three different options exhibit varying strengths and weaknesses depending on the period of the day, the season, and latitude. The observations suggest that BSE-1979 have important roles to play in hmF2 modeling and that the approach of modeling hmF2 from observed M(3000)F2 cannot be entirely jettisoned. Hence, there is a need for a robust ionosonde-derived hmF2 and M(3000)F2 database, for improved modeling efforts.

Turbulence generated small-scale structures as PMWE formation mechanism: Results from a rocket campaign

Simultaneous measurements of rocket-borne and ground-based instruments in a common volume were performed from Andøya, Norway (69° N, 16° E) in frame of the recent PMWE-project, devoted to clarify the formation mechanism behind polar mesosphere winter echoes (PMWE). This article focuses on measurements of April, 13th 2018. Despite low solar activity, we observe several radar echoes, giving the launch criterion. Combining precise in-situ ionization gauge and wave propagation measurements with ground-based radar measurements on 53.5 and 3.17 MHz, as well as lidar, we were able to measure key parameters of PMWE formation. Carefully analyzing the atmospheric background (i.e., temperature, viscosity, Brunt-Väisälä frequency, and scale heights of electron and neutral density), deriving turbulence parameters by means of radar and rocket, as well as estimating particle sizes of meteor smoke particles (MSP), we got a deep insight into the physical processes behind the PMWE phenomenon. Measurements clearly show that the coherent structures in refractive index variations (forming PMWE) are accompanied by neutral air turbulence, which is reflected in small-scale structures (down to some meters) of neutral and electron density. We analyze and discuss the temporal development of the radar echos by means of spectral width and wind measurements. We show that the behavior of the structures under investigation together with the atmospheric background is consistent with the interpretation, that PMWE were created by turbulence. Furthermore, it becomes clear that charged Meteor Smoke Particles (MSP) and background electron density can only enhance SNR, while turbulence is a prerequisite for their formation.

Reconstruction of Electron-Density Height Profiles Based in the Bottomside Ionosphere on Topside Satellite Sounding Data with the IRI Model

Reconstruction of Electron-Density Height Profiles Based in the Bottomside Ionosphere on Topside Satellite Sounding Data with the IRI Model

On the Altitude Patterns of Photo‐Chemical‐Equilibrium in the Martian Ionosphere: A Special Role for Electron Temperature

AbstractThe ionosphere at Mars is governed by photo‐chemical‐equilibrium (PCE) at and below the height of maximum electron density (∼130 km), while the topside ionosphere blends PCE with other processes (e.g., plasma dynamics). We studied the altitude profile from 135 to 260 km where PCE conditions transition to the non‐PCE domain. Using MAVEN observations of electron density (Ne) and temperature (Te), CO2 densities, and integrated energy flux Fsun(5–93 nm), we tested the PCE relationship (Mendillo et al., 2017, https://doi.org/10.1002/2017ja024366). We found high correlations coefficients (CC = 80–90%) for heights 25–40 km above hmax, and then decreases to CC = 50% (defining partial PCE control). Surprisingly, CCs returned to > 50% in the 160–175 height range. We found the re‐establishment of PCE control occurs where the Te values rise sharply and thereby reduce the plasma recombination rate due to its inverse dependence on electron temperature. Enhancements in the topside ionosphere due to that process were first postulated by Fox and Yeager (2006, https://doi.org/10.1029/2006JA011697) to explain the “shoulder” seen Ne(h) profiles from radio occultation experiments. MAVEN data now provide the first comprehensive set of in situ observations to relate this enigmatic “bulge” to observed PCE parameters. Moreover, MAVEN observations reveal that additional sources are present to account for the Ne enhancements larger than possible from the thermal process alone.

Assessment of IRI-2016 hmF2 model predictions with COSMIC observations over the African region

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.

Study of ionospheric D region changes during solar flares using MF radar measurements

During solar flares, the X-ray radiation suddenly increases, resulting in an increase in the electron density of the atmospheric D region and a strong absorption of short-wave radio waves. Based on Langfang medium frequency (MF) radar, this paper analyzed the variation characteristics of D region in the lower ionosphere from 62 km to 82 km. The analysis focused on multiple C-level and M-level solar flare events before and after the large-scale flare event at 11:53 (UT) on September 6, 2017. The results show that it is difficult to detect the electron density over 70 km in Langfang during solar flares, but the electron density value can be obtained as low as 62 km, and the stronger the flare intensity, the lower the detectable electron density height. Besides, the equal electron density height, the received power of X and O waves will also be significantly reduced during the flares, and the reduction of equal electron density height has a weak linear relationship with flare intensity.

Comparison and evaluation of a bottom-up GPS-RO electron density retrieval for D and E regions using radar observations and models

The lack of reliable global E-region electron density or conductivity measurements has hampered a detailed and quantitative understanding of the E-region electrodynamic processes. The characterization of the global E-region ionospheric irregularities as a function of local time, longitude, and season remains a great challenge. In this study, we evaluate the electron densities retrieved by Wu (2018) in the D and E regions using ground-based radar data and empirical models. Unlike in the conventional top-down retrieval methodology, the new approach avoids the Abel weighting function that carries substantial sensitivity to the electron density residuals from the F-region even after they have been corrected. The new technique uses a bottom-up approach in which the F-region contributions in the excess phase are more effectively removed compared to the Abel inversion, and hence more accurate electron density retrievals in D and E regions are determined. The results are compared and evaluated with two low and mid-latitude incoherent scatter radar observations — the Arecibo Observatory’s 430 MHz radar, located in Puerto Rico (18∘N, 67∘W) and the Millstone Hill Observatory’s 440 MHz radar, located in Massachusetts (42∘N, 72∘W). In addition, the results are also compared with two models — the International Reference Ionosphere model (IRI-2016) and the Faraday International Reference Ionosphere model (FIRI-2018) at these two locations. The comparison of electron density height profiles from GPS-RO retrievals at the two locations show good agreement with radar measurements, as well as the FIRI-2018 model predictions, especially at ∼ 85–100 km. The seasonal and diurnal climatology comparisons of GPS-RO retrieved electron density show good agreement with radar observations at both locations, and also reflect the influence of the solar cycle on E-region electron density. It is noticed that the GPS-RO background electron density at Millstone Hill increases by ∼ 20% at around 105 km from solar minimum to the maximum during cycle 24 which is in agreement with radar observations and FIRI-2018 model predictions.

Validation of International Reference Ionosphere model (IRI-2016) for F-region peak electron density height (hmF2): Comparison with Incoherent Scatter Radar (ISR) and ionosonde measurements at Millstone Hill

In this report, we have evaluated the performance of International Reference Ionosphere (IRI-2016) model in predicting the diurnal variation of F-region peak electron density height (hmF2) at Millstone Hill (MH, 42.6°N, 288.5°E) during the solar cycle 24 for both high and low-solar activity years. The new methodology is adopted to derive hmF2 values from the Incoherent Scatter Radar (ISR) measurements. The hmF2 derived from ISR along with ionosonde measurements operating at MH has been used to evaluate the performance of IRI-2016 model. The IRI-2016 model has three options to predict hmF2, namely, BSE-1979, AMTB-2013, and SHU-2015. The observed hmF2 from ISR and ionosonde are compared with all the three options provided by IRI-2016 to predict hmF2. Results show that hmF2 from IRI-2016, ISR and ionosonde exhibit similar diurnal variation. The deviations between measurements and model predictions were found to increase during nighttime. The SHU-2015 model emerged out to be the best in predicting the hmF2 values over MH as compared to other two options. The BSE-1979 option also provides reasonably better prediction as compared to the relatively latest AMTB-2013 options. Based on this statistical analyses, we recommend SHU-2015 option of IRI-2016 hmF2 model over MH area.

Response of the electron density profiles to geomagnetic disturbances in January 2005

The ionospheric response to geomagnetic storms is usually investigated by considering the variability of the critical frequency of the F2-layer (foF2) or the total electron content (TEC) because these two parameters are directly measured by the ionosonde stations and the Global Navigation Satellite Systems (GNSS). In the present paper, however, the reaction is explored by using the vertical profiles of the electron density, N(h), reconstructed by manually scaled ionosonde measurements at the station Sofia (42.4°N, 23.2°E). The mid-latitude ionosheric response to three geomagnetic storms that occurred in January 2005 is presented as this period has been selected because no major sudden stratospheric warming occurred during this month, and the winter 2005 is given in the literature as an example of a “normal” year. Hence the observed ionospheric response to the considered geomagnetic storms can be attributed mainly to the external forcing. Besides the traditional parameters foF2 and TEC, a particular attention is paid to the variability of the peak electron density height (hmF2). This study reveals for the first time that the main contribution to the response of the midlatitude ionosphere to moderate/intense winter geomagnetic storms is associated with significant enhancements of short-period quasi-diurnal oscillations with period of 6–7 hours observed in both foF2 and hmF2. An explanation of the main mechanisms responsible for the distortion of the diurnal ionospheric variability during these storms is offered. This result is especially important for the ground-based HF radio communications.

Responses of the D region ionosphere to solar flares revealed by MF radar measurements

Electron density (Ne) and effective reflection height (H', where the electron density reaches its peak value) in the D region observed by medium frequency (MF) radar at Kunming (25.6°N, 103.8°E) were utilized to quantitatively study the ionospheric response to solar flares. It was found that the H' and Ne had profound responses to solar flares. The results showed a sharp decrease in the H' from 76 to 80 km during the non-flare period to nearly 58 km with flares, and a sudden increase in the Ne from below 4×108 m3 in non-flare period to 1.8×109 m3 during 13 M-level flares. The behavior of Ne was strongly and positively correlated with the variation of the X-ray flux, with the largest coefficient being 0.93, while the changes of H' exhibited a strongly negative correlation of −0.96 with that of the X-ray flux. Moreover, variations of H' and ΔNe depended on not only the flare level, but also upon the onset time and duration of flare.

Ground-based Observations of the Polar Region Space Environment at the Jang Bogo Station, Antarctica

Jang Bogo Station (JBS), the second Korean Antarctic research station, was established in Terra Nova Bay, Antarctica (74.62°S 164.22°E) in February 2014 in order to expand the Korea Polar Research Institute (KOPRI) research capabilities. One of the main research areas at JBS is space environmental research. The goal of the research is to better understand the general characteristics of the polar region ionosphere and thermosphere and their responses to solar wind and the magnetosphere. Ground-based observations at JBS for upper atmospheric wind and temperature measurements using the Fabry-Perot Interferometer (FPI) began in March 2014. Ionospheric radar (VIPIR) measurements have been collected since 2015 to monitor the state of the polar ionosphere for electron density height profiles, horizontal density gradients, and ion drifts. To investigate the magnetosphere and geomagnetic field variations, a search-coil magnetometer and vector magnetometer were installed in 2017 and 2018, respectively. Since JBS is positioned in an ideal location for auroral observations, we installed an auroral all-sky imager with a color sensor in January 2018 to study substorms as well as auroras. In addition to these observations, we are also operating a proton auroral imager, airglow imager, global positioning system total electron content (GPS TEC)/scintillation monitor, and neutron monitor in collaboration with other institutes. In this article, we briefly introduce the observational activities performed at JBS and the preliminary results of these observations.

Auroral ionospheric E region parameters obtained from satellite-based far ultraviolet and ground-based ionosonde observations: 1. Data, methods, and comparisons.

A large number (~1000) of coincident auroral far ultraviolet (FUV) and ground-based ionosonde observations are compared. This is the largest study to date of coincident satellite-based FUV and ground-based observations of the auroral E region. FUV radiance values from the NASA Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Global Ultraviolet Imager (GUVI) and the Defense Meteorological Satellite Program (DMSP) F16 and F18 Special Sensor Ultraviolet Spectrographic Imager (SSUSI) are included in the study. A method is described for deriving auroral ionospheric E region maximum electron density (NmE) and height of maximum electron density (hmE) from N2 Lyman-Birge-Hopfield (LBH) radiances given in two channels using lookup tables generated with the Boltzmann 3-Constituent (B3C) auroral particle transport and optical emission model. Our rules for scaling (i.e., extracting ionospheric parameters from) ionograms to obtain auroral NmE and hmE are also described. Statistical and visual comparison methods establish statistical consistency and agreement between the two methods for observing auroral NmE, but not auroral hmE. It is expected that auroral non-uniformity will cause the two NmE methods to give inconsistent results, but we have not attempted to quantify this effect in terms of more basic principles, and our results show that the two types of NmE observations are well correlated and statistically symmetrical, meaning that there is no overall bias and no scale-dependent bias.

On the Use of Topside RO‐Derived Electron Density for Model Validation

AbstractIn this work, the standard Abel inversion has been exploited as a powerful observation tool, which may be helpful to model the topside of the ionosphere and therefore to validate ionospheric models. A thorough investigation on the behavior of radio occultation (RO)‐derived topside electron density (Ne(h))‐profiles has therefore been performed with the main purpose to understand whether it is possible to predict the accuracy of a single RO‐retrieved topside by comparing the peak density and height of the retrieved profile to the true values. As a first step, a simulation study based on the use of the NeQuick2 model has been performed to show that when the RO‐derived electron density peak and height match the true peak values, the full topside Ne(h)‐profile may be considered accurate. In order to validate this hypothesis with experimental data, electron density profiles obtained from four different incoherent scatter radars have therefore been considered together with co‐located RO‐derived Ne(h)‐profiles. The evidence presented in this paper show that in all cases examined, if the incoherent scatter radar and the corresponding co‐located RO profile have matching peak parameter values, their topsides are in very good agreement. The simulation results presented in this work also highlighted the importance of considering the occultation plane azimuth while inverting RO data to obtain Ne(h)‐profile. In particular, they have indicated that there is a preferred range of azimuths of the occultation plane (80°–100°) for which the difference between the “true” and the RO‐retrieved Ne(h)‐profile in the topside is generally minimal.

Ionospheric disturbances following the March 2015 geomagnetic storm from GPS observations in China

When strong solar activities and geomagnetic storms happen, satellite communications and navigation system will be strongly disturbed. It is of great significance to monitor ionospheric disturbances, because empirical models cannot capture ionospheric anomalous disturbances well. Nowadays, dual-frequency GPS (Global Positioning System) observations can be used to estimate the ionospheric total electron content, correct the ionospheric delay and analyze the response of the ionosphere to geomagnetic storms. In this paper, the ionospheric response to the geomagnetic storm occurred in March 2015 is investigated using GPS observations provided by Crustal Movement of Observation Network of China. The result shows that this storm increases the electron density in the ionosphere quickly and disrupts the structure of the northern equatorial anomaly region at the beginning. In the main process stage, compared with that in the quite periods, the VTEC (Vertical Total Electron Content) around the longitude of 120°E decreases by 50% and the amount of depletion is larger in the high latitude region than that in the low latitude region. We also find the height of the peak electron density in F2 layer increases during the geomagnetic storm from the electron density profiles derived from GPS occultation mission.

An improved empirical formulation of an ionosphere bottomside electron density profile thickness parameter

An improved empirical formulation for the characterization of the “base point” of the bottomside ionospheric electron density profile is proposed. The “base point” in an ionospheric layer is defined by the electron density profile height where the gradient dN/dh reaches a maximum. The difference between the height of the maximum electron density and the height of the “base point” is proportional to the ionospheric F2 layer thickness parameter B2. The previous empirical formula links the maximum value of dN/dh to foF2 and M(3000)F2 scaled from the ionograms. The new formulation adds a dependence on the solar zenith angle. The use of the new equation improves substantially the calculation of the B2 thickness parameter used in the NeQuick model.

Warm Ionized Medium throughout the Sagittarius–Carina Arm

Abstract Wisconsin H-Alpha Mapper observations of Hα and [S ii] λ6716 emission are used to trace the vertical distribution and physical conditions of the warm ionized medium along the Sagittarius–Carina arm. CO emission, tracing cold molecular gas in the plane of the Galaxy, is used as a guide to isolate Hα and [S ii] λ6716 emission along individual spiral arms. Exponential scale heights of electron density squared (or emission measure) are determined using Hα emission above (below) the midplane to be along the near Sagittarius arm, along the near Carina arm, and along the far Carina arm. The emission measure scale height tends to increase as a function of Galactocentric radius along the Sagittarius–Carina arm for . Physical conditions of the ionized gas are analyzed using the [S ii]/Hα line ratio, which more closely traces I Hα than height above the plane, z, suggesting a stronger relationship with the in situ electron density. We interpret this result as further evidence for the majority of the observed diffuse emission originating from in situ ionized gas as opposed to scattered light from classical H ii regions in the plane.

Diurnal variations of the ionospheric electron density height profiles over Irkutsk: Comparison of the incoherent scatter radar measurements, GSM TIP simulations and IRI predictions

The long-duration continuous Irkutsk incoherent scatter radar (ISR) measurements allowed us to obtain the monthly averaged height-diurnal variations of the electron density in the 180–600km altitudinal range for 4 four seasons (winter, spring, summer, autumn) and for two solar activity levels (low and moderate). Considering these electron density variations as “quiet ionosphere patterns” we compared them with the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) simulations and the International Reference Ionosphere (IRI) predictions. It was found that some observational features revealed from the ISR measurements are reproduced nicely by both the theoretical and empirical models, and some features agree better with the GSM TIP than with IRI. None of the models is able to reproduce a detailed multi-peak behavior of the electron density observed by ISR at ∼300km and above for the spring and autumn under low solar activity, while for the spring the GSM TIP tends to reproduce the morning and daytime peaks at the same local times as they are seen from the ISR observations.