Effects Of Ionospheric Disturbances Research Articles

IONOSPHERIC TEMPORAL-SPATIAL CORRELATION ANALYSIS USING GNSS NETWORKS OVER CHINA

Abstract. The Global Navigation Satellite System (GNSS) is well recognized as a valuable tool for studying ionospheric variation, providing a means to measure variations in the Total Electron Content (TEC) of the ionosphere. In this manuscript, we focus specifically on the use of GNSS networks to study ionospheric diurnal variation over China, highlighting some of the key findings and challenges in this area. We begin by describing the basic principles of GNSS-based TEC measurements. We then analyze ionospheric diurnal variation using about 320 GNSS stations in China, including the Southern, Middle, and Northern areas. We also discuss some of the challenges associated with GNSS-based TEC measurement and analysis, such as the effects of receiver and satellite biases and understanding of spatial–temporal TEC variation. Finally, we highlight the sunset enhancement and scintillation of GNSS-based ionospheric diurnal variation research. Overall, this abstract provides a valuable overview of the use of GNSS networks for studying ionospheric diurnal variation and its potential applications for improving space weather forecasting and mitigating the effects of ionospheric disturbances on GNSS-based navigation systems.

A new model for total electron content based on ionospheric continuity equation

With the development of the Global Navigation Satellite System (GNSS), the accuracy and reliability requirements on observations are constantly increasing. The effect of ionospheric disturbance is not negligible, especially for accurate GNSS applications. To reduce the influence of ionospheric delay and disturbance, this study uses the Ionospheric Continuity Equation (ICE) to establish a new model for Total Electron Content (TEC), which takes both photochemical and transportation processes into account and named ICE model. Experimental results show that the ICE model achieves accuracies higher than Spherical Harmonic (SH) and polynomial models on geomagnetism quiet and disturbance days, and more prominent advantages appear at nighttime. By the test of Satellite Differential Code Bias (SDCB) estimation, the deviations of the polynomial and the ICE models are nearly the same whatever the geomagnetic field is quiet or disturbance; however, the estimation accuracy of the ICE model is slightly better than the polynomial model. Spatial and temporal adaptability tests indicate that the ICE model can achieve accuracies of 0.5 TECU and 1 TECU on time scales of approximately 25 min and 100 min, respectively. On the weak disturbance or quiet day, these accuracies can be achieved on the spatial scales of approximately 200 km and 600 km. The credibility of the ICE model is evaluated by Nash–Sutcliffe efficiency. The evaluation results assigned that the ICE model has higher credibility than the SH and polynomial models and better immunity to geomagnetic disturbance.

Comparison between ionospheric disturbances caused by barium and cesium

After being released in the ionosphere, alkali-metal atoms will be rapidly photoionized by solar UV, producing positive ions and electrons, and forming artificial plasma cloud. Based on a three-dimensional two-species fluid model, considering both the loss of barium atoms due to photoionization and oxidation and the influence of horizontal wind field in the release region, the spatial-temporal evolution of the artificial plasma cloud is discussed. By taking into account the electromagnetic field force, pressure gradient, particle collisions and ion inertia, the ionospheric disturbance effects caused by barium and cesium are compared with each other. The simulation results show that the alkali metal rapidly expands after being released in the ionosphere, and the generated plasma cloud gradually forms an ellipsoidal structure from the inside to the outside under the constraint of magnetic field with considering no wind. Meanwhile, the expanded plasma cloud pushes away the background oxygen ions, forming an oxygen ion density hole in the release center and two symmetrical density bumps on both sides. In the absence of neutral wind, the plasma cloud is dominated by the movement along magnetic field, while considering the background neutral wind, the plasma cloud and background disturbance area will move along the direction of wind, so that the density gradient of plasma cloud becomes steepening on the upwind side. Although the movement of ion cloud across the magnetic field is constrained, the neutrals can pass through the magnetic field freely, so the ion cloud and neutral cloud will separate from each other slowly. Also, the presence of horizontal wind field will make a greater disturbance to the background oxygen ion. By comparing the simulation results of barium and cesium we can see that, qualitatively, the expansion characteristics of Cs<sup>+</sup> and Ba<sup>+</sup> as well as their effects on the background O<sup>+</sup> are similar. Due to the small diffusion coefficient of cesium, the barium cloud expands more rapidly and the coverage area of Ba<sup>+</sup> cloud is wider. Because of the large photoionization rate of cesium, the ionization yield of cesium is higher than that of barium when the same mass is released. In addition, the snowplow effect of Cs<sup>+</sup> is stronger than that of Ba<sup>+</sup>, and the oxygen ion density holes and bumps caused by Cs<sup>+</sup> are also larger.

Numerical Simulation of Ionospheric Disturbance Effects by Chemical H<sub>2</sub>O Release

为充分研究化学物质在电离层释放的扰动效应和后期发展效果，基于化学物质在电离层的扩散模型、化学反应和电离层扩展F的控制模型，通过电离层H₂O的释放，研究电子e，H₂O，O⁺和H₂O⁺共4种粒子的分布状态，分析点源、多源和线源释放对电离层的扰动效果，比较不同高度、不同量和不同时间释放的影响结果，模拟夜间释放后期所激发的扩展F发展差异.结果表明，H₂O在电离层释放后，能有效耗散背景电子形成空洞，O⁺和H₂O⁺数密度呈椭圆形分布；点源、多源和运动目标线源等不同释放方式对电离层的扰动效果不同，证实了人工影响一定形态和区域电离层的可能性；H₂O释放扰动幅度，低层大于高层，白天强于夜晚，释放量越多扰动越突出；夜间化学释放能激发扩展F，并且释放量越多，激发效果越好.

Meteorological effects of ionospheric disturbances from vertical radio sounding data

We studied ionospheric disturbances caused by the wave-like processes in the middle atmosphere. The ionospheric data were obtained from continuous measurements with the DPS-4 vertical sounding ionosondes in Irkutsk and Norilsk over 2008–2010. The ionospheric disturbances were considered as deviations of the F2 layer peak density variations from the daily average values. We also used ECMWF ERA-Interim reanalysis data for the middle atmosphere dynamics analysis, and the Aura MLS data on the atmospheric temperature at the stratosphere and upper mesosphere heights obtained within the above period. The analysis allowed us to reveal periods of middle-scale wave motions in the stratosphere and lower mesosphere during winter seasons in the Northern Hemisphere. The wave motions observed in the study were associated with the jet streams at the stratosphere/lower mesosphere heights localized mainly between 50 and 80°N. The middle-scale waves in the stratosphere were compared with ionospheric disturbances over two ionosonde stations in Irkutsk and Norilsk. A noticeable increase in the wave activity was found at the F2 layer heights during the periods of stratospheric wave activity. For both stations, the maximal variability in the ionosphere F2 layer parameters was observed in winter with the minimal variability observed in summer. The summer–winter difference was more pronounced in the case of the high-latitude ionosonde in Norilsk.

Assessment and Mitigation of Ionospheric Disturbance Effects on GPS Accuracy and Integrity

Ionospheric disturbances affect Global Positioning System (GPS) performance in terms of accuracy and integrity, especially over the equatorial region. During the period of the disturbances, GPS receivers suffer from a high noise level. Not taken into account by the current stochastic model, the ionospheric disturbances degrade GPS positioning accuracy. In addition, non-Gaussian tails are observed in the distribution of the noise during the period of the disturbances; therefore the integrity of GPS can also be affected. This paper develops a statistical solution that is able to mitigate effects of ionospheric disturbances on GPS accuracy and integrity using a commercial dual frequency receiver. The Rate of Total Electron Content (TEC) change Index (ROTI), a parameter derived from the dual frequency receiver, is used to group the levels of ionospheric disturbances. The standard deviations of the pseudorange noise under different groups are evaluated. By incorporating both the ROTI and the satellite elevation, a modified stochastic model is proposed to reduce the effect of the disturbed observation on the positioning accuracy. The performance of the model is evaluated by a test and an inflated sigma for each group is recommended for over-bounding anomalies of observations to protect the user against threats from ionospheric disturbances. This technique, together with results in this paper, can be applied to mitigate the effects of ionospheric disturbances on GPS.

태양폭풍에 의한 전리층 교란이 신속정지측위 정확도에 미치는 영향

There exists a high correlation between the ionospheric delays and the integer ambiguity in GPS observation equation, so that the sufficient time span is required to revolve the integer ambiguity. This means that the ambiguity resolution plays a key role especially in rapid-static positioning mode. To analyze the effect of ionospheric disturbances on the positioning accuracy, 02/19/2011 day of dataset was selected processed in rapid-static positioning mode. The total of 141 30-minute sessions were processed, i.e., the estimation procedure started every 10 minutes, and the time-to-fix information of each data interval is obtained. In this study, the analysis is performed by comparing the time-to-fix with the magnitudes of ionospheric delays. The computed correlation coefficient between the time-to-fix and the magnitudes of ionospheric delays is 0.31, which indicates the ionospheric disturbances affect the positioning accuracy in rapid-static positioning mode. Therefore, it is required to collect and process sufficient data when the GPS surveying is performed in unfavorable ionospheric conditions.

Density Perturbations in the Upper Atmosphere Caused by the Dissipation of Solar Wind Energy

The upper atmosphere constitutes the outer region of the terrestrial gas envelope above about 100 km altitude. The energy budget of this outer gas layer is partly controlled by the dissipation of solar wind energy. Since this energy input is largely irregular, the resulting density changes are considered as perturbations. The properties and physics of such density perturbations are reviewed here. Besides being an important link in the complex chain of solar-terrestrial relations, such disturbances are also of practical interest because they affect the orbits of satellites and space stations and are responsible for ionospheric disturbance effects.

F layer postsunset height rise due to electric field prereversal enhancement: 1. Traveling planetary wave ionospheric disturbance effects

An ionospheric sounding station is operational at Palmas (10.2°S, 48.2°W, dip latitude 5.5°S), Brazil, since 2002. Observations of F layer virtual height day‐to‐day variations during evening hours (1800 LT to 2000 LT) show a strong variability, even during geomagnetically quiet periods. From the ionospheric multifrequency virtual height variations (at 3, 4, 5, 6, 7, and 8 MHz), observed from July 2003 to May 2004, it is found that the virtual height day‐to‐day variability presents oscillations with periods of days during the evening hours. The thermospheric wind component perpendicular to the magnetic meridian (zonal wind) is one of the primary sources that generate the F region dynamo near sunset, which causes the zonal electric field prereversal enhancement (PRE) that induces the E × B vertical F layer postsunset height rise. Therefore, the planetary wave (PW) component that flows superposed on the thermospheric wind induces a traveling planetary wave ionospheric disturbance (TPWID) on the vertical F layer displacement. This indicates that the postsunset ionospheric height rise can be strongly modulated by TPWID oscillations. Our study shows that TPWIDs with periods of several days control the strength of the electric field PRE and, therefore, slowly push the F layer heights up or down, according to the TPWID phase. Also, simultaneous virtual height variations at Sao José dos Campos (low latitude) and Palmas (equatorial region) for October and November show similar behavior. This suggests that TPWID oscillation is a manifestation of atmospheric equatorial Kelvin waves that modulate the thermospheric wind.

Climatology of GPS ionospheric scintillations over high and mid-latitude European regions

Abstract. We analyze data of ionospheric scintillation in the geographic latitudinal range 44°–88° N during the period of October, November and December 2003 as a first step to develop a "scintillation climatology" over Northern Europe. The behavior of the scintillation occurrence as a function of the magnetic local time and of the corrected magnetic latitude is investigated to characterize the external conditions leading to scintillation scenarios. The results shown herein, obtained merging observations from four GISTM (GPS Ionospheric Scintillation and TEC Monitor), highlight also the possibility to investigate the dynamics of irregularities causing scintillation by combining the information coming from a wide range of latitudes. Our findings associate the occurrences of the ionospheric irregularities with the expected position of the auroral oval and ionospheric troughs and show similarities with the distribution in magnetic local time of the polar cap patches. The results show also the effect of ionospheric disturbances on the phase and the amplitude of the GPS signals, evidencing the different contributions of the auroral and the cusp/cap ionosphere.

Updating the IRI ionospheric model for effects of substorms

The effect of ionospheric disturbances occurring during a substorm or a sequence of substorm is modeled as an additive correction to the quiet IRI foF2 and hmF2 values which depends on the time since the onset of the substorm and on the maximum AE-index value reached in it. This can reduce the changes of hmF2 from 30 – 40% to 10 – 15%; the disturbed electron density profile is reproduced quite satisfactory too.

Polar ionospheric disturbance effects on NNSS satellite positioning

From the analysis of the United States Navy navigation satellite system (NNSS) positioning data of about 10000 passes, it is clearly found that polar ionospheric disturbance affects the positioning. The positioning error increases with increasing geomagnetic disturbance level (local K-index), and the pass number of position fixes decreases by one or two per day when the K-index is large. These effects may arise from the spatial gradients of electron density and/or the radio wave scattering due to well-developed ionospheric irregularities inherent to the disturbed auroral ionosphere.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Broadside excitation of ELF by a horizontal dipole beneath a sporadic E environment: Theory

A simple surface propagation model is commonly used to estimate the effects of ionospheric disturbances on extremely low frequency (ELF) propagation. Though often adequate, one shortcoming of the model is its failure to allow for excitation by the broadside component of a horizontal electric dipole. That excitation can be quite significant in a sporadic E environment because the modal polarization can then contain a substantial mixture of transverse electric component. This is demonstrated by considering a flat earth geometry with a vertical geomagnetic field superimposed on a laterally homogeneous, cylindrically symmetric disturbance centered over the transmitter. The method utilizes normal mode decomposition. Matching equations at the boundary of the disturbance are developed by evaluating height gain integrals, and it is shown that this method is tantamount to simply matching the ground vertical electric and azimuthal magnetic fields at the boundary. Results for a sporadic E type environment indicate substantial departures from other model predictions.

Magnetic storm associated perturbations of the upper atmosphere: Recent results obtained by satellite‐borne gas analyzers

This review summarizes some of the recent results on the disturbed upper atmosphere obtained by satellite‐borne gas analyzers. According to these measurements, magnetospheric activity leads to the development of two different disturbance zones. The high‐ and middle‐latitude region is characterized by an increase in the heavier constituents Ar, N2, and O2, by a height‐dependent behavior of O, and by a significant decrease of He. The reaction time of the atmosphere is much smaller than one orbital period. At lower latitudes a moderate increase of all constituents is observed. A comparison between atmospheric and ionospheric data demonstrates that, in contrast to positive effects, negative ionospheric storms are closely coupled to changes in the neutral composition. In addition, model calculations fully support a causal relation between both phenomena. Given this correlation, atmospheric and negative ionospheric disturbance effects have certain variations in common. These include systematic changes with the magnetic storm intensity, with magnetic position, with local time, and with season. Whereas the presently available empirical and theoretical models are quite capable of reproducing the basic properties of the observed atmospheric perturbations, these algorithms are not sophisticated enough for a more detailed description of the data.

Results of ionospheric drift measurements in the f region

Results of ionospheric drift measurements at Banaras (geographic latitude 25.31° N, geographic longitude 83° E) during night hours for the years 1957-59 are reported. The seasonal and diurnal variations in the apparent velocity and the apparent direction obtained by similar-fade analysis are shown with the help of histograms and polar diagrams. The effect of ionospheric disturbances on the drift measurement is discussed. Assuming that the isometric irregularities are deformed into a characteristic ellipse, the axial ratio and the orientation of the characteristic ellipse are calculated. Using these parameters, the true velocity and the true direction of the drift is determined. Results are shown with the help of histograms and polar diagrams. The field alignment of the irregularities is discussed.

Backscatter experiments during the total eclipse of October 2, 1959

Backscatter records taken at 19.39 Mc/s with a rotating antenna were investigated in order to determine how the returns were affected by the total eclipse of October 2, 1959. At the frequency chosen, ground backscatter via F-layer reflection sets in before sunrise at the location of observation. On normal days before and after the eclipse, it appears first in the east and south-east and then, 2 or 3 hours later, in the west. On the eclipse day, the signal from the east was delayed by several hours and appeared after the return from the west had been received. Graphical representations of details of the backscatter records show not only the eclipse effect but also the effect of ionospheric disturbances on days before and after the eclipse. These disturbances make it nearly impossible to formulate a standard of average behavior that may be quantitatively compared with the eclipse day. The long duration of the eclipse effect indicates its complicated nature, which probably involves dynamic properties of the F2 layer.

A new index of solar activity based on ionospheric measurements

The monthly mean relative sunspot number ( R M ) is assumed to contain a component ( R v ) which has a one-to-one correlation with the critical frequency of the F 2-layer in an undisturbed ionosphere and which is, therefore, an idealized index of solar activity. The residual component ( R x ) may be regarded as an error which has a Standard Deviation of about 20 per cent. A new index ( I F 2) has been constructed for the period 1938–1954; like R M , it can also be regarded as giving an approximate value of R v , but its residual error component ( R z ) has an S.D. which is only about one tenth that of R x . The magnitude of I F 2, for a given month is computed from the mean noon critical frequencies in the F 2-layer at Slough, Huancayo, and Watheroo, which are normally available within a few weeks of the end of each month. The index is based, in effect, on a calibration of the F 2-layer critical frequencies at these observatories in terms of R v , using data extending back as far as possible. Precautions have been taken to reduce to negligible proportions the effects of ionospheric disturbances on the magnitude of the new index.

A review of present knowledge of the ionospheric propagation of very-low, low- and medium-frequency waves

The paper deals with the ionospheric propagation of waves of frequencies less than 3 Mc/s and is confined mainly to transmission over medium and long distances (greater than 500 km). The results of investigations on low and very-low frequencies (less than 300 kc/s) are summarized under the headings of field strength, phase and polarization measurement, the effects of ionospheric disturbances, the study of local ionospheric characteristics and theoretical studies. Since our knowledge of medium-frequency propagation was adequately summarized in a report64 in 1937, only work done since that date has been considered here. An important item of the recent work is the study of ionospheric cross-modulation. The paper concludes with a summary of our present knowledge of the subject and recommendations for further studies.

Some developments in commercial point-to-point radiotelegraphy

Developments in point-to-point radiotelegraphy have been concerned chiefly with the improvement of reliability to facilitate the introduction of time-division multiplex systems using direct-printing equipment, and to ensure continuous communication over difficult circuits such as those to the antipodes.Methods of reception using frequency-shift keying are discussed in relation to distortion, interference and multi-path effects; figures are given for the results of tests with this system compared with those of the on/off keying system. In one case, the lost capacity due to poor radio conditions was reduced by 39%.Radiotelegraph relays are described which cover interruption of direction communication, and charts are included to show the recovery of lost time. Owing to the introduction of radio relay stations at Barbados and Colombo, the periods when no communication is possible between this country and Australia have been reduced to negligible proportions. The effects of ionospheric disturbances on the London–Montreal route have also been greatly reduced by the use of radio relay stations at Ascension and Barbados; the station at Ascension has been in use since 1939.Equivalent phase modulation of short-wave transmitters is discussed or use with long-distance facsimile circuits.Concerning aerials, the development of horizontal-dipole receiving arrays to augment the vertical broadside-beam array, is dealt with; also a review of wideband coupling devices for coupling balanced aerials to coaxial feeders. Mention is made of the advantages of remotely controlled and unattended radio transmitters in reducing congestion on radio-station sites and in minimizing personnel.The paper also deals with telegraph printing systems; the doublecurrent cable-code system is described, and compared with 5-and 7-unit systems for undetectable errors and flexibility of operation.A frequency-modulated v.f. system for the control of radio stations is described.Finally, under the general heading of miscellaneous telegraph equipment, the paper contains a description of a high-speed photo-electric morse transmitter and an electronic keying device.

Emission of Light by Solid Nitrogen and the Origin of the Auroral Spectrum

The monthly mean relative sunspot number (RM) is assumed to contain a component (Rv) which has a one-to-one correlation with the critical frequency of the F2-layer in an undisturbed ionosphere and which is, therefore, an idealized index of solar activity. The residual component (Rx) may be regarded as an error which has a Standard Deviation of about 20 per cent. A new index (IF2) has been constructed for the period 1938–1954; like RM, it can also be regarded as giving an approximate value of Rv, but its residual error component (Rz) has an S.D. which is only about one tenth that of Rx. The magnitude of IF2, for a given month is computed from the mean noon critical frequencies in the F2-layer at Slough, Huancayo, and Watheroo, which are normally available within a few weeks of the end of each month. The index is based, in effect, on a calibration of the F2-layer critical frequencies at these observatories in terms of Rv, using data extending back as far as possible. Precautions have been taken to reduce to negligible proportions the effects of ionospheric disturbances on the magnitude of the new index.