Lower Ionosphere Research Articles

Comparison and Verification of the Different Schemes for the Ionization‐Recombination Cycle of the Ionospheric D‐Region

AbstractThis study presents the results of a comparison and verification of three plasma‐chemical models of the lower ionosphere, which describe the dynamics of 4, 5, and 8 charged components under calm conditions and during X‐ray flares of different classes. As a result of verification of the constructed schemes for the ionization‐recombination cycle using data on the propagation of very low frequency signals during 12 X‐ray flares, the best agreement with experimental measurements was obtained with the eight‐component model of the ionospheric D‐region. On two of the four paths, this model successfully simulated the qualitative and quantitative response of the amplitude‐phase characteristics to solar flares in the C, M, and X classes. In contrast to the eight‐component model, four‐ and five‐component models are of limited accuracy which could not be noticeably increased by correcting the ionization rate calculation or the input values of the neutral parameters of the atmosphere.

Отклик ионосферы на прохождение тайфунов по наблюдениям методом СДВ-радиопросвечивания

The response of the lower ionosphere to the passage of several dozen typhoons has been studied using a regional network of VLF stations in the Russian Far East. The experimental data presented in all cases clearly demonstrates wavelike disturbances of the subionospheric VLF signal amplitude and phase during the active stage of typhoons crossing radio paths. With the exception of magnetoactive and seismoactive days, this means that the disturbances generated by a typhoon, when propagating into the upper ionosphere, pass through the lower ionosphere, causing corresponding disturbances in the amplitude and phase of the VLF signal. Spectral analysis shows that the range of the wave disturbances detected corresponds to the periods of atmospheric internal gravity waves (IGW). A mechanism of the action of IGWs on the lower ionosphere is proposed which allows us to interpret the VLF signal phase variations observed. According to this mechanism, the action of IGW on the lower ionosphere is caused by polarization fields arising during the wave motion of plasma in the lower part of the F layer. These fields projected along geomagnetic field lines into the lower ionosphere cause the upper wall of the Earth—ionosphere waveguide to rise or fall.

Ionospheric response to the passage of typhoons observed by subionospheric VLF radio signals

The response of the lower ionosphere to the passage of several dozen typhoons has been studied using a regional network of VLF stations in the Russian Far East. The experimental data presented in all cases clearly demonstrates wavelike disturbances of the subionospheric VLF signal amplitude and phase during the active stage of typhoons crossing radio paths. With the exception of magnetoactive and seismoactive days, this means that the disturbances generated by a typhoon, when propagating into the upper ionosphere, pass through the lower ionosphere, causing corresponding disturbances in the amplitude and phase of the VLF signal. Spectral analysis shows that the range of the wave disturbances detected corresponds to the periods of atmospheric internal gravity waves (IGW). A mechanism of the action of IGWs on the lower ionosphere is proposed which allows us to interpret the VLF signal phase variations observed. According to this mechanism, the action of IGW on the lower ionosphere is caused by polarization fields arising during the wave motion of plasma in the lower part of the F layer. These fields projected along geomagnetic field lines into the lower ionosphere cause the upper wall of the Earth—ionosphere waveguide to rise or fall.

On anomalous wind amplitudes in the lower ionosphere

According to known experiments both the zonal and meridional components of the wind demonstrate a clear increase in amplitude, starting from heights of 80–85 km, and the maximum amplitudes, which are reached at altitudes of 100–110 km. With a further increase in altitude, a gradual decrease in amplitudes begins. The wind maximum amplitudes turn out to be much larger than predicted by the theory of tidal movements in the ionosphere or the empirical Horizontal Wind Model (HWM). We propose a simple two-dimensional model to indicate the cause of abnormal amplitudes of wind motion in the lower ionosphere. The model is based on the existence of a well-established Ekman wind profile at the heights of the mesosphere-thermosphere.

Seasonal and Diurnal Dynamics of Radio Noise for 8–20 MHz Poleward‐Oriented Mid‐Latitude Radars

AbstractBased on ray tracing in a smooth ionosphere described by the IRI‐2012 model we have inferred the seasonal‐diurnal dynamics of radio noise observed by four mid‐latitude high‐frequency (HF) radars. In the calculations, noise is assumed to be homogeneous and stationary, but the main contribution comes from the radar skip zone boundary due to focusing radiowaves effect. Noise absorption along the ray path is simulated from the IRI‐2012 electron density, and from the molecular nitrogen density and electron temperatures obtained from the NRLMSISE‐00 model. Earth magnetic field is not taken into account both in the absorption and ray‐tracing calculations due to insufficient accuracy of the ionospheric model. The model results are compared with experimental radar data, and good agreement between the two is demonstrated. It is shown that experimentally observed seasonal and diurnal dynamics of the noise correlates well with model predictions. We demonstrated saturation effect at low noise levels. The model makes it possible to estimate the amount of absorption in D‐ and E‐layers using noise observations at SuperDARN and SuperDARN‐like poleward‐oriented radars, especially at mid‐latitudes. This is important for the retrieval of long term variations in the electron density in the lower ionosphere, by using wide coverage provided by these radars' network. The model also makes it feasible to interpret vertical absorption by experimental noise observations, thereby significantly expanding the capability of HF radars to monitor the lower ionosphere, and to provide data for joint analysis with other data, obtained by these radars at E‐ and F‐layer heights.

Martian Ionospheric Magnetic Fluctuations Below 200 km

AbstractWe conduct a search for 5–16 Hz magnetic waves below 200 km and within the Martian ionosphere using data from multiple instruments onboard the Mars Atmosphere and Volatile EvolutioN mission spacecraft. We present a case study and an analysis of the 54 identified events to establish trends. Nearly half the wave events occur near the cusps of strong crustal magnetic fields (CMFs). The stronger regions have fewer events and may be a result of stronger CMFs preventing draped field lines from reaching lower altitudes. A majority of the observed magnetic waves occur on the nightside, are associated with greater fluxes of electrons traveling downward along the local magnetic field compared to those traveling upward, and correspond to increases in thermal plasma density. These aspects indicate electron precipitation was present during these wave events. We conclude that the waves are observed under magnetic field conditions favorable for the penetration of electrons and waves into the lower ionosphere, but that the electron precipitation cannot solely account for the waves or plasma changes.

Multi‐Instrument Observations of the Ionospheric Response to the 26 December 2019 Solar Eclipse Over Indian and Southeast Asian Longitudes

AbstractHere, the impact of the 26 December 2019 solar eclipse on the equatorial and low latitude ionosphere has been investigated using ground and space‐based observations over Indian and Southeast Asian longitudes. The high‐resolution Ionosonde observations at Tirunelveli, GPS Total Electron Content (TEC) observations from a chain of GPS receivers along and across the eclipse path, TIMED‐SABER, and Ionospheric Connection Explorer (ICON) satellites were utilized to investigate the eclipse‐induced variations in electron density and thermospheric cooling. We noticed a tremendous increase and decrease in the base height of the F‐layer, resembling the nighttime Pre‐Reversal Enhancement (PRE). Near the eclipse maximum, a strong blanketing sporadic E layer was observed at Tirunelveli with a top frequency of ∼18 MHz for 1 hr and 26 min. Satellite traces (STs) and “U” shaped ionograms were noticed for the first time over Tirunelveli during eclipse maximum and end phases. The “STs” and “U” shaped traces indicate the presence of short‐period gravity waves or TID type of wave perturbations over the Indian region. A maximum of ∼5–7 TECU (30%–40%) decrease in TEC is observed on the eclipse day for iisc, hyde, and tiru stations. Periodogram analyses of TEC data showed the presence of wavelike structures with periodicities of 18–24 min for different stations. Simultaneous observations from the ICON satellite showed an increase and decrease in hmF2 and NmF2 which matches well with the ionosonde observations from Tirunelveli. The temperature profiles from TIMED‐SABER and ICON satellites showed a reduction and enhancement in the lower and upper E regions respectively.

CSES Satellite Observations of 50 Hz Power Line Radiation Over Mainland China and Its Response to COVID‐19

AbstractWe present a low‐altitude satellite survey of power line harmonic radiation (PLHR) at 50 Hz over Mainland China. We analyzed the month‐to‐month variation pattern in PLHR occurrence rate and further analyzed its correlation with some influencing factors (i.e., solar radiation, lightning flashes, and electricity consumption) using CSES satellite electric field data from 2019 to 2021. We also investigate the response of PLHR occurrence rate to COVID‐19. The statistical results show the dayside PLHR occurrence rate decreasing from winter to summer solstice and increasing from summer to winter solstice, which indicates it is controlled by the solar radiation. The nightside variation is more complex, which may be due to many sources that could influence the nightside lower ionosphere. The PLHR occurrence rate significantly decreased over Mainland China in February 2020, which is because of the significant decrease in electricity consumption due to the suspension of industrial production caused by COVID‐19.

Investigation of gravity wave characteristics in the equatorial ionosphere during the passage of the 15 January 2010 solar eclipse over Tirunelveli

Solar eclipses are known to produce gravity wave disturbances in the atmosphere–ionosphere system in addition to density reduction due to temporary changes in solar radiation. The magnetic equator is ideally located to investigate these waves and their coupling to the equatorial ionosphere due to its unique geometry. Accordingly, the response of the equatorial ionosphere to a rare Annular Solar Eclipse (ASE) observed on 15 January 2010 is investigated using high-resolution observations from Canadian Advanced Digital Ionosonde (CADI) located at Tirunelveli which is a magnetic equator and on the eclipse totality path in India. In addition, simultaneous observations of GPS TEC from Tirunelveli, electron density profiles from Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC), and Equatorial Electrojet (EEJ) strength were analysed. The real height analysis has been performed on the ionosonde data using POLynomial ANalysis (POLAN). The isoheight/isofrequency analysis has been performed using real height on eclipse and control days. The results indicate a reduction of ∼33% in the lower ionosphere whereas no change has been noticed close to the F layer peak on the eclipse day. The isoheight analysis further indicates the presence of gravity waves with dominant periods in the range of 5–30 min. Further analyses have been performed on the altitude variation of dominant waves and their amplitudes/phases using ionosonde to identify whether they are generated in situ or propagated from below. The altitude variation of group and phase velocities showed opposite propagation indicating that they were propagated from the below. In addition, the simultaneous presence of gravity waves in the fmin, TEC, and EEJ strength on eclipse day supports our finding that these waves were propagated from the lower atmosphere.

Investigation of the Reaction of Schumann Resonances to Short Transient Geophysical Events Under the Influence of Atmospheric Electromagnetic Noise

AbstractThe interference of electromagnetic signals from lightning discharges in the frequency range below 100 Hz is the source of a global electromagnetic phenomenon in the Earth's atmosphere known as the Schumann resonance (SR). Changes in the parameters of SR signals caused by geophysical disturbances make it possible to study the state and dynamics of the lower ionosphere. When calculating the SR parameters, there are problems associated with the impact of electromagnetic interference of natural and anthropogenic origin. The main natural sources of interference are signals associated with the radiation of nearby lightning discharges, as well as the influence of the Alfvén ionospheric resonator. The paper presents a new method for calculating the SR parameters, which makes it possible to find the spectra distorted by interference, mention above, and exclude them from further processing. The developed technique significantly increased the temporal resolution of the obtained data on the frequency and amplitude of the SR. Due to this, it became possible to study the influence of fast heliogeophysical disturbances (such as solar X‐ray flares) on the lower ionosphere and, as a consequence, on the parameters of the SR. An analysis of the experimental data made it possible to establish a linear dependence of the SR frequency on the logarithm of the X‐ray flux in the range up to 0.2 nm during a class X solar flare.

An Amateur-Radio-Based Open-Source (HW/SW) VLF/LF Receiver for Lower Ionosphere Monitoring, Examples of Identified Perturbations

The ground-based monitoring of the lower ionosphere by studying the perturbations of the subionospheric propagation of very-low-frequency/low-frequency (VLF/LF) signals is important in the research of a wide variety of geophysical and Sun/space extreme phenomena. Such perturbations are identified as anomalies in the signal received from the VLF/LF transmitters operating worldwide for military purposes, time code broadcasting, etc. Especially for the study of local ionosphere-influencing phenomena, such as earthquakes, volcanoes, typhoons, etc., the monitoring of several subionospheric propagation paths is necessary. However, it is very difficult to find in the market (or reproduce) hardware (HW) for wide-band VLF/LF receivers that could receive many different transmitters, while the involved software (SW) is mainly proprietary. Aiming to provide a low-cost and easy-to-build alternative for the scientists involved in this research field, we suggest a VLF/LF receiver setup based on amateur radio open-source HW and SW. Its key components are the so-called “mini-whip” active antenna and the freeware “SpectrumLab” and “GPS2Time”. The full HW schematics and all settings of the employed SW configuration for the proposed VLF/LF receiver setup are provided in the article. To check the reliability of the proposed receiver setup, two almost identical VLF/LF radio receivers were installed in the prefecture of Attica in Greece, in June and September of 2021, respectively. Examples of ionospheric perturbations due to different phenomena (solar flares, earthquakes, and a magnetic storm) are provided to show the ability of the proposed receiver setup to provide reliable data for ionosphere-related research.

Arecibo measurements of D-region electron densities during sunset and sunrise: implications for atmospheric composition

Abstract. Earth's lower ionosphere is the region where terrestrial weather and space weather come together. Here, between 60 and 100 km altitude, solar radiation governs the diurnal cycle of the ionized species. This altitude range is also the place where nanometre-sized dust particles, recondensed from ablated meteoric material, exist and interact with free electrons and ions of the ionosphere. This study reports electron density measurements from the Arecibo incoherent-scatter radar being performed during sunset and sunrise conditions. An asymmetry of the electron density is observed, with higher electron density during sunset than during sunrise. This asymmetry extends from solar zenith angles (SZAs) of 80 to 100∘. This D-region asymmetry can be observed between 95 and 75 km altitude. The electron density observations are compared to the one-dimensional Sodankylä Ion and Neutral Chemistry (SIC) model and a variant of the Whole Atmosphere Community Climate Model incorporating a subset SIC's ion chemistry (WACCM-D). Both models also show a D-region sunrise–sunset asymmetry. However, WACCM-D compares slightly better to the observations than SIC, especially during sunset, when the electron density gradually fades away. An investigation of the electron density continuity equation reveals a higher electron–ion recombination rate than the fading ionization rate during sunset. The recombination reactions are not fast enough to closely match the fading ionization rate during sunset, resulting in excess electron density. At lower altitudes electron attachment to neutrals and their detachment from negative ions play a significant role in the asymmetry as well. A comparison of a specific SIC version incorporating meteoric smoke particles (MSPs) to the observations revealed no sudden changes in electron density as predicted by the model. However, the expected electron density jump (drop) during sunrise (sunset) occurs at 100∘ SZA when the radar signal is close to the noise floor, making a clear falsification of MSPs' influence on the D region impossible.

Numerical modelling of sub-ionospheric Very Low Frequency radio signal anomalies during the Samos (Greece) earthquake (M = 6.9) on October 30, 2020

Lower ionospheric perturbation during earthquake activity is well recognized by the anomalous behavior of Very Low or Low Frequency (VLF/LF) radio signal. In this study, we present the sub-ionospheric VLF signal modulation during the Samos earthquake that took place on October 30, 2020 (M = 6.9). We use the conventional terminator time method to check the seismogenic impression in the VLF signal during the local sunrise and sunset times. VLF signals from two transmitters ISR (Israel) and TBB (Turkey) are used for this analysis and those are recorded in a receiving station UWA in Greece. Both signals show a strong shift in the sunrise and sunset terminator times. The signal profiles are numerically simulated using the Long Wavelength Propagation Capability (LWPC) program by incorporating Wait’s two-component ionospheric parameters (β and h′). The simulation gives highly satisfactory outcomes. The outputs of LWPC are used to compute the electron density profile of the lower ionosphere. It is found that the electron density gets significantly modulated during the maximum shift in the terminator times. The electron density is found to have both increased and decreased from its normal value before the earthquake. The VLF path dependency is strongly observed in the change in the electron density profile. For ISR-UWA, nighttime reflection height has been computed using the modal conversion technique, and it is found to be similar to the LWPC outcomes. The overall condition was geomagnetically quiet, and the results have no contamination due to solar-terrestrial interaction.

Analysis of Pre-Earthquake Space Electric Field Disturbance Observed by CSES

In order to explore the abnormal disturbance of the space electric field caused by earthquakes using the electric field data of the ULF and VLF frequency bands of the electric field observed by the ZH-1 satellite, and taking the Mw7.7 earthquake in the Caribbean Sea in the southern sea area of Cuba on 29 January 2020 as an example, the signal-to-noise ratio of the NAA and NLK artificial source VLF transmitting stations in the Northern Hemisphere and the height of the lower ionosphere was calculated. The disturbance of the electric field in the ULF band was extracted using the S-G filtering method. The results indicate that: (1) The ionospheric anomaly caused by this earthquake appeared 20 days before the earthquake, and before the earthquake, there were significant anomalous changes in all parameters within the pregnant seismic zone. The signal-to-noise ratios of the NAA and NLK artificial source transmitter stations decreased by 30%, and the height of the low ionosphere decreased by 5–10 km, while there were anomalous perturbations in several orbits of the ULF electric field, and the magnitude of the perturbations exceeded three times the standard deviation. (2) The SNR of the artificial source transmitting stations before and after the earthquake was significantly reduced in the third period before the earthquake and recovered after the earthquake. (3) The low ionospheric height appears to be reduced before the earthquake and recovers after the earthquake. (4) The decrease in the S/N ratio occurred simultaneously with the decrease in ionospheric height 15 days–10 days before the earthquake. This provides a reference for extracting pre-earthquake ionospheric precursor anomalies.

Can Radioactive Emanations in a Seismically Active Region Affect Atmospheric Electricity and the Ionosphere?

—Anomalous variations in radon emissions from the soil are sometimes observed before and after strong earthquakes. In this paper, we theoretically analyze the known hypothesis that these variations in radioactive emanations in the surface layer of the atmosphere cause variations in the vertical background current in the atmosphere with subsequent changes in the electron density {{n}_{e}} in the lower ionosphere. For this purpose, we will first assess the relation between radon emission variations and the vertical atmospheric current flowing into the ionosphere. Then we will solve a model problem concerning the spatial distribution of plasma density and electric field perturbations occurring in the E-layer of the ionosphere caused by an inflowing vertical current. It was believed that the current flowing into this layer contains only an electron component and is attenuated only by the recombination of electrons. The estimate of the maximum variation {{n}_{e}} is at least 3–5 orders of magnitude smaller than the observed anomalous variations, which allows us to conclude that this hypothesis is not plausible.

Distinct ionospheric response to three different geomagnetic storms during 2016 using GPS-TEC observations over the Indian equatorial and low latitude sectors

The ionospheric response during three distinct geomagnetic storms occurred in the year 2016 is investigated using GPS-TEC observations in the Indian equatorial and low latitude sectors. The three geomagnetic storms are considered for this study which were occurred on 20 January 2016 (2230 LT), 6 March 2016 (0230 LT) and 13 October 2016 (0530 LT) with minimum Sym-H values of −95 nT, −110 nT and −114 nT respectively. These three geomagnetic storms are different from one another in the sustainment of main and recovery phases and are occurred at three different local times corresponding to the Indian longitudes. This study brings out the major differences of these three geomagnetic storms characteristics and their distinct effects on the equatorial and low latitude ionosphere. Significant changes in the VTEC during main and recovery phases of these three storms are found to be mainly associated with prompt penetration electric fields and thermospheric neutral compositional changes. During the storm of 20 January 2016, positive storm effects during main and recovery phases of the storm are in association with the penetration electric fields. The complete main phase for the 6 March 2016 geomagnetic storm was occurred during night time and no changes in VTEC has been identified, which could be due to the weak background electron density. A positive storm effect is noticed during the recovery phases of the storms of 6 March 2016 and 13 October 2016, due to the storm induced electric fields differences and in particular due to the enhanced [O]/[N2] ratio in thermospheric composition. A strong positive storm effect caused by Co-rotating Interacting Region (CIR) induced disturbances after the 13 October 2016 storm is also discussed.

Unexpected Regional Zonal Structures in Low Latitude Ionosphere Call for a High Longitudinal Resolution of the Global Ionospheric Maps

This study reports unexpected strong longitudinal structures from Global Navigation Satellite System (GNSS) derived total electron content (TEC) observations in the low-latitude ionosphere over Asia. The observations during 2019–2020 show diverse patterns in the zonal difference of regional TEC, even under geomagnetically quiet conditions. The TEC in the northern hemisphere occasionally exhibits drastic zonal gradients. The intense regional gradients in TEC span a longitudinal extent of about 20°. The higher values may appear on the east or the west side. Strong zonal gradients may appear in all seasons, regardless of geomagnetically quiet or active conditions. The 15 December 2019 and 16 March 2020 cases depict an intense zonal differences cluster in the narrow latitudinal band of 16°N to 28°N, spanning a regional scale smaller than the normal longitudinal structures. In contrast, the Global Ionospheric Maps (GIMs) with a longitudinal resolution of 5° show a much flatter zonal picture. Such intense and regional-scale zonal structures in the low-latitude ionosphere call for a high zonal resolution of GIMs in terms of better geographically distributed observations. Notably, no counterpart regional structures are found at the conjugated points in the southern hemisphere during the two cases. Although the physical drivers are not certain, the appearance only in the northern hemisphere possibly excludes the dominant contribution to forming the regional structures from the equatorial electric field.

Dual Sounding Rocket and C/NOFS Satellite Observations of DC Electric Fields and Plasma Density in the Equatorial E- and F-Region Ionosphere at Sunset.

E × B plasma drifts and plasma number density were measured on two NASA rockets launched simultaneously at sunset from Kwajalein Atoll with apogees of 182 and 331 km, with similar, coincident measurements gathered on the Communications/Navigation Outage Forecasting System (C/NOFS) satellite at 390 km. The combined measurements portray a highly dynamic ionosphere in a narrow range of local time and altitude, providing evidence of vortex‐like motions. Although the vertical plasma drift was upwards, its magnitude was not constant, increasing between ∼150 and 250 km altitude where the plasma density was reduced. The zonal plasma drifts displayed a shear with altitude, changing from eastward to westward flow below 270 km, coincident with the larger upward drifts and consistent with the maintenance of the vortex flow. The plasma density on the western flank was highly structured compared to the eastern flank, despite the fact that the western region corresponded to slightly earlier local times. These observations illustrate that the low latitude ionosphere at sunset must be considered as an ensemble of interconnected flows encompassing an evolving “theater,” as opposed to a background that simply unfolds linearly with respect to local time. The observations also underscore how satellites at high altitudes do not capture the highly dynamic ionosphere and thermosphere at the lower altitudes which are critical for understanding the electrodynamics system. Such motions set the stage for large scale plasma instabilities to form later in the evening, as observed by radars at Kwajalein and subsequent passes of the C/NOFS satellite.

Standing Alfvén Waves Within Equatorial Plasma Bubbles

AbstractPlasma depletions in the disturbed equatorial ionosphere are known to be associated with magnetic fluctuations and Alfvén waves. Here, using data from the Swarm B satellite's vector field magnetometer and electric fields instrument at an altitude of ∼500 km, we present evidence of standing Alfvén modes trapped within strong density depletions. Fourier transforms of electric (δE) and magnetic (δB) perturbations reveal harmonic structure with anticorrelated peaks and relative phase shifts approaching ±90°, in agreement with a simple model of standing waves sampled from a moving spacecraft. The mode frequencies allow us to estimate the field‐aligned length of the bubbles, which we find to be in the range of 110–200 km. This value is much smaller than the overall field line length mapped to the two E‐region footprints, indicating that the waves we observe do not couple to the lower ionosphere.

Three‐Dimensional Reconstruction of Tongue of Ionization During the 11 October 2010 Geomagnetic Storm and Evolution Analysis With TIEGCM

AbstractThe three‐dimensional computerized ionospheric tomography (3DCIT) technique that fused multisource data is used to reconstruct the spatial distribution of tongue of ionization (TOI) appeared over Greenland during a moderate geomagnetic storm on 11 October 2010. The reconstruction results are validated with observations from the constellation observing system for meteorology, ionosphere, and climate radio occultations and two ionosonde stations, which show good agreements. The 3DCIT images indicated a zone of high electron density (magnitude of ∼5 TECU) that crossed northern Greenland and electrons were input into the polar region in the anti‐sunward direction after aggregating at midlatitudes, which formed a TOI. The images also revealed that the TOI magnitude was larger in the upper ionosphere ssand lower at 300 and 500 km but still noticeable. Below 300 km, the TOI was difficult to detect. The simulation result of the Thermosphere‐Ionosphere‐Electrodynamic General Circulation Model (TIEGCM) also showed the same TOI structure. Then, we combined the measured ionospheric data and term‐by‐term analysis of the ion continuity formula in TIEGCM to further identify the principal TOI formation mechanisms. We assume that the dominant TOI formation mechanism is electric field transport, which is offset by ambipolar diffusion and neutral wind transport. Furthermore, the uplift of electrons and the insignificant effect of other physical processes explained the insignificant TOI in lower ionosphere.