Electron Density Irregularities Research Articles

On the Factors Controlling the Relationship Between Type of Pulsating Aurora and Energy of Pulsating Auroral Electrons: Simultaneous Observations by Arase Satellite, Ground‐Based All‐Sky Imagers and EISCAT Radar

AbstractPulsating Aurora (PsA) is one of the major classes of diffuse aurora associated with precipitation of a few to a few tens of keV electrons from the magnetosphere. Recent studies suggested that, during PsA, more energetic (i.e., sub‐relativistic/relativistic) electrons precipitate into the ionosphere at the same time. Those electrons are considered to be scattered at the higher latitude part of the magnetosphere by whistler‐mode chorus waves propagating away from the magnetic equator. However, there have been no actual cases of simultaneous observations of precipitating electrons causing PsA (PsA electrons) and chorus waves propagating toward higher latitudes; thus, we still do not quite well understand under what conditions PsA electrons become harder and precipitate to lower altitudes. To address this question, we have investigated an extended interval of PsA on 12 January 2021, during which simultaneous observations with the Arase satellite, ground‐based all‐sky imagers and the European Incoherent SCATter (EISCAT) radar were conducted. We found that, when the PsA shape became patchy, the PsA electron energy increased and Arase detected intense chorus waves at magnetic latitudes above 20°, indicating the propagation of chorus waves up to higher latitudes along the field line. A direct comparison between the irregularities of the magnetospheric electron density and the emission intensity of PsA patches at the footprint of the satellite suggests that the PsA morphology and the energy of PsA electrons are determined by the presence of “magnetospheric density ducts,” which allow chorus waves to travel to higher latitudes and thereby precipitate more energetic electrons.

The Impact of Vertical Plasma Motion on the Evolution of Predawn Equatorial Plasma Bubbles on the Dayside

AbstractThis study investigates the impact of vertical ionospheric drift during daytime on the evolution of predawn equatorial plasma bubbles by conducting model simulations using “Sami3 is Another Model of the Ionosphere.” The upward drift of the ionosphere transports bubbles to higher altitudes, where their lifetime is set by the atomic oxygen photoionization rate. While the bubbles generated at predawn persist into dayside, the bubbles generated shortly after sunset diminish before sunrise. Therefore, post‐sunset bubbles do not contribute to daytime electron density irregularities. Bubbles maintain their field‐aligned characteristics throughout the daytime regardless of the vertical ionospheric drift. This property allows bubbles to exist near the magnetic equator despite poleward plasma transport by the fountain process. The shift of irregularity concentration to higher latitudes over time in satellite observations is explained by the combined effect of transport of bubbles to higher altitudes and rapid refilling of depletions near the magnetic equator.

Classification of Ionospheric Scintillations during high Solar Activity and Geomagnetic Storm over Visakhapatnam Region using Machine Learning Approach

The ionospheric plasma disturbances typically correlate with irregularities in electron density and ionospheric scintillations are produced in reaction to these variations generating radio signal fluctuations. Geolocation services and space based communication are endangered due to ionospheric scintillation which promptly produces fluctuations in information collected by Global Navigation Satellite Systems and this is at its strongest when the solar cycle is at its peak. Ionospheric space weather has a significant impact on Global Navigation Satellite Systems (GNSS) and one crucial aspect used in investigating ionospheric characteristics is total electron content (TEC). Due to fluctuations in time and space, the TEC obtained from GNSS signals is nonlinear and nonstationary. In this study, machine learning approaches for Classification of the ionospheric scintillations were used during the high solar activity and geomagnetic storm in the month of July 2023. This approach enables the classification of ionospheric phase scintillations using well-known classifiers: Decision Tree and Support Vector Machine.

Space-based GNSS radio signals to investigate ionospheric plasma changes preceding the 2016 Al Hoceima-Morocco earthquake, Mw=6.4

This paper examines abrupt variations in ionospheric electron density preceding the Al Hoceima earthquake (January 25th, 2016, Mw = 6.4, Northern Morocco). The observed anomalous behavior in the F2-ionospheric region, at about 350 km altitude, raises the possibility of a connection with impending seismic activity of moderate-to-great magnitude, supporting the hypothesis that Total Electron Content (TEC) variations could serve as potential earthquake precursors. For this purpose, we have exploited one of the main ionospheric keys, TEC, through a network of over one hundred dual-frequency Global Positioning System/Global Navigation Satellite Systems (GPS/GNSS) receivers. Through calculation algorithms based on spherical harmonic analysis of GPS/GNSS Observation-Navigation data, we were able to produce local ionospheric maps to restore the GPS-TEC signal and investigate potential ionospheric disturbances associated with this shallow-focus and strong earthquake. Since the ionospheric TEC is a function of the variability and dynamics of the Earth’s ionosphere, mainly time-space and solar-geomagnetic activities, we had to consider each of these disturbing factors separately. In fact, the seismic zone of Al Hoceima (Morocco, North Africa), at about 35°N latitude, belongs to the region of low geographical latitudes. In such regions the variations of the ionospheric layer are slight. Moreover, during the earthquake preparation period, space weather conditions exhibited a calm state characterized by low solar activity and the absence of geomagnetic storms. The adequate effects of these physical conditions allow us, through wavelet transform, to emerge solely signatures of earthquake-related ionospheric disturbances. Based on the seismo-ionospheric combination model, we have highlighted some ionospheric electron density irregularities that decreased abnormally, near the epicenter several days prior to the 2016 Al Hoceima main event. From these findings, we can state that such research provides a promising approach for predicting earthquakes through large fluctuations in the ionized shell of the Earth’s atmosphere, thereby offering the prospect of a life-saving seismic alarm.

Two‐Component Phase Scintillation Spectra in the Auroral Region: Observations and Model

AbstractThe random amplitude and phase fluctuations observed in trans‐ionospheric radio signals are caused by the presence of electron density irregularities in the ionosphere. Ground‐based measurements of radio wave signals provide information about the medium through which these signals propagate. The Canadian High Arctic Ionospheric Network (CHAIN) Global Position System (GPS) receivers record radio signals emitted by the GPS satellites, enabling the study of their spectral characteristics. This study presents examples of phase spectra with two power‐law components. These components exhibit steeper spectral slopes at higher frequencies and shallower ones at lower frequencies. To be more specific, we conducted a spectral characterization of sixty one (61) events recorded by the CHAIN Churchill GPS receiver, which is located in the auroral oval. When fluctuations above the background level are only observed in the phase, the spectra tend to be systematically steeper. Conversely, the power increase in higher frequency fluctuations accompanying amplitude scintillation tends to result in shallower spectra. A basic yet powerful model of radio wave propagation through a turbulent ionosphere, characterized by a power law electron density spectrum, can help to explain the two power laws observed in the scintillation events presented in this study by identifying the role played by small‐scale ionospheric irregularities in diffraction.

Multi‐Instrument Observations of Various Ionospheric Disturbances Caused by the 6 February 2023 Turkey Earthquake

AbstractIn this work, we investigate various types of ionospheric disturbances observed over Europe following the earthquake that occurred in Turkey on 6 February 2023. By combining observations from Doppler sounding systems, ionosondes, and GNSS receivers, we are able to discern different types of disturbances, propagating with different velocities and through different mechanisms. We can detect co‐seismic ionospheric disturbances close to the epicenter, as well as ionospheric signatures of acoustic waves propagating as a consequence of propagating seismic waves. Unlike the vast majority of past ionospheric co‐seismic disturbance studies that are primarily based on Total Electron Content variations, reflecting disturbances propagating around the F‐region peak, the focus of the present study is the manifestation of disturbances at different ionospheric altitudes by exploiting complementary ionospheric remote sensing techniques. This is particularly highlighted through ionospheric earthquake‐related signatures established as specific ionogram deformations known as multiple‐cusp signatures which appear as additional cusps at the base of the F‐region attributed to electron density irregularities generated by Rayleigh surface waves that generate acoustic waves propagating up to the ionosphere. Therefore this study underlines the advantage that multi‐instrument investigations offer in identifying the propagation of earthquake‐related ionospheric disturbances at different ionospheric altitudes and distances from the earthquake epicenter.

On the In Situ Observations of Irregularities During Rocket Flights From Thumba for Different Geophysical Conditions and the Associated Causative Mechanisms

AbstractElectron density and Neutral Wind (ENWi) probe and/or Langmuir probe were flown on three different rocket flights from equatorial station Thumba (8.5°N, 77°E), during daytime, eclipse time, and post sunset time respectively, of low solar activity period, to study ionization irregularities in the E region of the ionosphere. The spectral characteristics observed using the payloads were analyzed during the three different rocket flights. The 15 January 2010 solar eclipse event and “SOUREX 1” wind and electron density measurements confirm the validity of the wind shear theory for equatorial regions during the eclipse and post sunset periods, when electrojet is weak, using wind and electron density irregularity measurements from the same instrument (ENWi) for the first time. The spectral indices in the range of −1.2 to −1.78 and the strong wind shear due to gravity wave winds during the eclipse time as well as the post sunset time, confirm the role of neutral turbulence in the generation of irregularities in the 95–112 km altitude region. The spectral index of −2.0 to −2.7 and the presence of irregularities in the negative gradient regions establishes the role of wind‐driven gradient drift instability (GDI) in generating irregularities during the SOUREX 1 post sunset flight for altitudes below 93 km. Further, the role of gradient drift instability in triggering ionization irregularities during the daytime on 14 January 2010 is unraveled by the spectral index of −2.03 and the presence of irregularities in the positive gradient regions alone.

Spectral Characteristics of Phase Fluctuations at High Latitude

AbstractIt has long been established that ionospheric electron density irregularities cause random rapid amplitude and phase fluctuations in trans‐ionospheric radio signals. Various types of ground‐based measurements, including radar and Global Navigation Satellite System (GNSS) receivers, have been utilized to gain insights into the plasma mechanisms that could lead to the development of these ionospheric irregularities. The spectral characteristics of radio wave signals emitted by GNSSs and detected by the Canadian High Arctic Ionospheric Network Global Positioning System (GPS) receivers are analyzed to try and identify the spectral signatures of the ionospheric plasma irregularities. In the polar region, we have confirmed that phase fluctuations in the GPS signal are not always accompanied by amplitude fluctuations. For the first time, a systematic comparison is conducted on the spectral properties of phase‐fluctuation events in the absence and presence of amplitude scintillations, respectively. More specifically, a spectral characterization is performed on 41 events recorded by three receivers positioned within the auroral oval. When fluctuations above the background level are solely observed in the signal's phase, the spectrum of phase variations exhibits a consistent steepness. Conversely, the presence of amplitude scintillation is accompanied by an increase in power at higher frequencies, resulting in shallower spectra. This analysis provides yet another physical element suggesting that the rapid fluctuations observed in the signal's amplitude may be caused by Fresnel‐scale irregularities arising from a gradient‐drift‐like instability while the phase variations seem to be consistent with a refractive mechanism caused by large‐scale ionospheric structures.

Simultaneous equatorial plasma bubble observation using amplitude scintillations from GNSS and LEO satellites in low-latitude region

This study estimates the scale sizes of the plasma density irregularities and the longitudinal width associated with equatorial plasma bubbles (EPBs) in equatorial and low-latitude regions. By analyzing amplitude scintillation S4 indices and total electron content (TEC) measured from low earth orbit (LEO) satellite’s beacon signals with 400 MHz and Global Navigation Satellite System (GNSS) L1/E1 signals with 1575.42 MHz, recorded by receivers at the KMITL station in Bangkok, Thailand (geographic; 13.73° N, 100.77°E, magnetic: 7.26°N), we investigate the characteristics of these irregularities. We collected data of 154 LEO satellite pass events during nighttime on 21 disturbed days in four equinoctial months in 2021. Based on the presence or absence of the scintillation effects on GNSS and LEO beacon signals, the events are categorized into four classes to estimate the scale size of the plasma density irregularities. The analysis suggests that events with both GNSS and LEO scintillations, as well as events with GNSS scintillation alone, occur predominantly before midnight assuming the presence of the small-scale size of the irregularities within EPB. However, events with only LEO scintillation occur throughout the whole night and some events are observed before the events with both GNSS and LEO scintillations. Post-sunset LEO scintillation alone may be attributed to the onset of EPBs developing at low altitude, while post-midnight LEO scintillation events near the magnetic equator, observed during periods of low GNSS Rate of TEC Index (ROTI) values, are associated with bottom-side ionospheric irregularities but are not linked with EPB. The findings are consistent with previous researches on the generation and decay of electron density irregularities within plasma bubbles. However, this study provides new insights by using specific data sets and analysis techniques, offering a more comprehensive understanding of the association of LEO scintillations with bottom-side ionospheric irregularities near the magnetic equator, not observed in the ROTI map.Graphical

Transformation of the Spatial Spectrum of Scattered Radio Waves in the Conductive Equatorial Ionosphere

The oblique radio wave incidence on a turbulent equatorial conductive collision plasma layer is considered. The “Compensation Effect” has been discovered by us. A complex refractive index of the equatorial terrestrial ionosphere has been derived for the first time. Second-order statistical moments of the spatial power spectrum (SPS) of scattered radio waves are obtained for the first time using the WKB method, taking into account the asymmetry of the problem: the inclined incidence of the wave on a plasma boundary and the asymmetry of the magneto-ionic parameters. It was established for the first time that a certain direction exists along which the inclined incidence radio wave on a plasma layer and the anisotropy parameters of a magnetoplasma compensate each other. This result will have great practical application in communication. In this case, the SPS of scattered radio waves neither widens nor is its maximum displaced. The behavior of this spectrum versus distance propagated by radio waves in the conductive equatorial ionosphere is analyzed numerically for different penetration angles and anisotropy factors of asymmetric anisotropy electron density irregularities. It was shown that the anisotropy factor of elongated plasmonic structures has a substantial influence on the “Compensation Effect” of scattered ordinary and extraordinary waves penetrating in the conductive collision ionospheric plasma the slab. Numerical calculations are carried out for the anisotropic Gaussian correlation function applying IRI experimental data.

Morphological and Spectral Features of Ionospheric Structures at E- and F-Region Altitudes over Poker Flat Analyzed Using Modeling and Observations

Electron density irregularities in the ionosphere modify the phase and amplitude of trans-ionospheric radio signals. We aim to characterize the spectral and morphological features of E- and F-region ionospheric irregularities likely to produce these fluctuations or "scintillations". To characterize them, we use a three-dimensional radio wave propagation model-"Satellite-beacon Ionospheric scintillation Global Model of upper Atmosphere" (SIGMA), along with the scintillation measurements observed by a cluster of six Global Positioning System (GPS) receivers called Scintillation Auroral GPS Array (SAGA) at Poker Flat, AK. An inverse method is used to derive the parameters that describe the irregularities by estimating the best fit of model outputs to GPS observations. We analyze in detail one E-region and two F-region events during geomagnetically active times and determine the E- and F-region irregularity characteristics using two different spectral models as input to SIGMA. Our results from the spectral analysis show that the E-region irregularities are more elongated along the magnetic field lines with rod-shaped structures, while the F-region irregularities have wing-like structures with irregularities extending both along and across the magnetic field lines. We also found that the spectral index of the E-region event is less than the spectral index of the F-region events. Additionally, the spectral slope on the ground at higher frequencies is less than the spectral slope at irregularity height. This study describes distinctive morphological and spectral features of irregularities at E- and F-regions for a handful of cases performed using a full 3D propagation model coupled with GPS observations and inversion.

Interpretation of Radio Wave Scintillation Observed through LOFAR Radio Telescopes

Abstract Radio waves propagating through a medium containing irregularities in the spatial distribution of the electron density develop fluctuations in their intensities and phases. In the case of radio waves emitted from astronomical objects, they propagate through electron density irregularities in the interstellar medium, the interplanetary medium, and Earth’s ionosphere. The LOFAR radio telescope, with stations across Europe, can measure intensity across the VHF radio band and thus intensity scintillation on the signals received from compact astronomical objects. Modeling intensity scintillation allows the estimate of various parameters of the propagation medium, for example, its drift velocity and its turbulent power spectrum. However, these estimates are based on the assumptions of ergodicity of the observed intensity fluctuations and, typically, of weak scattering. A case study of single-station LOFAR observations of the strong astronomical source Cassiopeia A in the VHF range is utilized to illustrate deviations from ergodicity, as well as the presence of both weak and strong scattering. Here it is demonstrated how these aspects can lead to misleading estimates of the propagation medium properties, for example, in the solar wind. This analysis provides a method to model errors in these estimates, which can be used in the characterization of both the interplanetary medium and Earth’s ionosphere. Although the discussion is limited to the case of the interplanetary medium and Earth’s ionosphere, its ideas are also applicable to the case of the interstellar medium.

The Occurrence Climatology of Equatorial Plasma Bubbles: A Review

Electron density irregularities in the equatorial ionosphere at night are understood in terms of plasma bubbles, which are produced by the transport of low-density plasma from the bottomside of the F region to the topside. Equatorial plasma bubbles (EPBs) have been detected by various techniques on the ground and from space. One of the distinguishing characteristics of EPBs identified from long-term observations is the systematic seasonal and longitudinal variation of the EPB activity. Several hypotheses have been developed to explain the systematic EPB behavior, and now we have good knowledge about the key factors that determine the behavior. However, gaps in our understanding of the EPB climatology still remain primarily because we do not yet have the capability to observe seed perturbations and their growth simultaneously and globally. This paper reviews the occurrence climatology of EPBs identified from observations and the current understanding of its driving mechanisms.

Multicomponent Diffusion of Dusty Plasma in PMSE Including the Growth of Dust Particles

AbstractDusty plasma diffusion was applied to model the plasma response to perturbations in dust density, which yields small‐scale irregularities in electron density that are responsible for Polar Mesosphere Summer Echos. Previous diffusion models treated aerosols either as fixed‐charge dust or as multiple‐charge‐state dust using chemical rate equations. The growth of aerosol particles was previously considered in the study of layered structures in mesospheric clouds, but it has not been incorporated into dust diffusion. In this paper, a multicomponent diffusion of a dusty plasma, consisting of electrons, ions, and charged aerosols, is developed, accounting for the growth of the aerosols. It is shown that, for typical parameters in polar mesopause region, the evolution of the density structures of the dusty plasma undergoes an initial charging process (approximately 100 s), then an ambipolar diffusion process on ion time scale (approximately hundreds of seconds), and the aerosol diffusion on dust time scale (>104 s). Furthermore, the growth of the aerosols retards the dust diffusion and causes the transition from anticorrelation to correlation between the electron and ion density perturbations (contrary to only anticorrelation or correlation as in the case without considering the growth). The growth also bends the density profiles from upward shifting to downward sedimentation. In addition, larger initial grain radius and the width of the initial perturbation result in slower diffusion. The diffusion is much faster at 88 km than at 82 km.

Temporal Spectrum of a Scattered Electromagnetic Waves in the Conductive Collision Turbulent Magnetized Plasma

Using WKB method the peculiarities of the temporal spectrum of an ordinary and extraordinary electromagnetic wave scattered in a weakly randomly inhomogeneous three-dimensional nonstationary and conductive magnetized plasma are investigated. On the basis of the stochastic differential transport equation for the frequency fluctuation the broadening and the displacement of the temporal spectrum for both waves are obtained for the polar terrestrial ionosphere. These statistical characteristics contains anisotropic parameters: velocity of a plasma stream, conductivities of the ionosphere, elongated electron density irregularities are characterized by the anisotropy factor and inclination angle with respect to the geomagnetic lines of forces. The analysis of the power spectrum of the waves as a function of the propagation distance and the nondimensional frequency parameter containing the carrier frequency and characteristic temporal scale of electron density fluctuations are carried out. Analytical and numerical calculations have shown that the terrestrial conductivity and anisotropy factors exert a substantial influence on evaluation of the temporal spectrum than the inclination angle. It was found that the wave spectrum increases initially as the square root of the propagation distance, but at large distances it approaches a limiting value. Statistical moments of a scattered ordinary and extraordinary waves do not depend on an absorption sign and valid for both absorptive and active media.

Multipoint Measurement of Fine‐Structured EMIC Waves by Arase, Van Allen Probe A, and Ground Stations

AbstractWe examined the growth and propagation of fine‐structured electromagnetic ion cyclotron (EMIC) waves related to time‐varying density irregularities using multipoint measurement data observed by Arase, Van Allen Probe A, and two ground‐based induction magnetometers (Gakona and Dawson) during a field line conjunction event on April 18, 2019. We analyzed the wave data obtained by the aforementioned spacecraft and stations, and found that the appearance of fine structures in the observed EMIC waves clearly coincided with the ambient electron density irregularities in the magnetosphere, which can cause periodic wave growth and waveguiding on their propagation. Furthermore, we found that the latitudinal widths of the EMIC wave activity region and the wave propagation duct were ∼185 km and less than 80 km at an auroral altitude of 100 km, respectively. We also found thermal ion heating ( eV/q) during the EMIC wave activity.

Spread F echoes variability along solar flux and seasonality conditions over the 50-MHz radar on Christmas Island/ Espalhe a variabilidade dos ecos de F ao longo do fluxo solar e das condições de sazonalidade no radar de 50 MHz na Ilha Christmas

Perturbations in the amplitude (or phase) of radio signals are caused by irregularities in the ionospheric electron density. Ionospheric structures can disrupt the propagation of radio waves, and are commonly observed, for instance, by ionospheric vertical radio sounders (ionosondes). For historical reasons, the signatures of ionospheric irregularities in different types observations (optical, radio, in-stu ) are referred to as equatorial spread F (ESF). Previous studies show that the occurrence rate can be greatly affected by solar and magnetic conditions. Observations during the period of 2003 to 2012 of nighttime echoes made from the 50-MHz radar on Christmas Island (2.0 o N, 157.4 o W) have revealed time and altitude pattern distribution along the descending phase of solar cycle 23 and the recent extended solar minimum phase. We present the study of spread F echoes as a function of solar flux conditions and seasonality in order to quantify their variability. Under higher solar flux conditions, echoes reach higher altitudes but decay earlier. Only during solar minimum conditions the echoes exist throughout the whole night, since the post?reversal anti?zonal background electric field is weaker. Thus, irregularities during solar maximum will be dominated by dynamics near the time of the PRE. Since the population of irregularities during solar minimum exists throughout the whole night, post?reversal ionospheric conditions may play a role in the morphology of plasma irregularities, especially with the coincidentally weaker PRE during solar minimum. Peak time occurrence of echoes along the current period show a well defined pattern, meanwhile the peak altitude occurrence of echoes show a slight regular pattern.

An EISCAT UHF/ESR Experiment That Explains How Ionospheric Irregularities Induce GPS Phase Fluctuations at Auroral and Polar Latitudes

AbstractA limitation to the use of Global Navigation Satellite System (GNSS) for precise and real‐time services is introduced by irregularities in the ionospheric plasma density. An EISCAT UHF/ESR experiment was conducted to characterize the effect of electron density irregularities on temporal fluctuations in TEC along directions transverse to GPS ray paths in the high latitudes ionosphere. Two representative case studies are described: Enhancements in temporal TEC fluctuations originating (a) in the auroral ionosphere following auroral particle precipitation and (b) in the polar ionosphere following the drift of a polar patch as well as particle precipitation. The results indicate that the origin of enhancements in TEC fluctuations is due to the propagation through large‐to‐medium scale irregularities (i.e., ranging from few kilometres in the E region to few tens of kilometres in the F region) and occurring over spatial distances of up to approximately in the E region and up to approximately in the F region with a patchy distribution. Furthermore, the results indicate that enhancements in TEC fluctuations produced by polar plasma patches and particle precipitation occur over similar temporal scales, thus explaining the overall observation of higher phase scintillation indices in the high‐latitude ionosphere. The similarity in the temporal scales over which enhancements in TEC fluctuations occur in the presence of both particle precipitation and plasma patches suggests an intrinsic limitation in the monitoring and tracking of plasma patches through ground GNSS observations.

Ionospheric Scintillation Prediction on S4 and ROTI Parameters Using Artificial Neural Network and Genetic Algorithm

Irregularities in electron density usually correlate with ionospheric plasma perturbations. These variations causing radio signal fluctuations, in response, generate ionospheric scintillations that frequently occur in low-latitude regions. In this research, the combination of an artificial neural network (ANN) with the genetic algorithm (GA) was implemented to predict ionospheric scintillations. The GA method was considered for obtaining the ANN model’s initial weights. This procedure was applied to GNSS observations at GUAM (13.58°E, 144.86°N, 201.922H) station for the daily prediction of ionospheric amplitude scintillations via predicting the signal-to-noise ratio (S4) or via prediction of the rate of TEC index (ROTI). Thirty-day modeling was carried out for three months in January, March, and July, representing different seasons of the winter solstice, equinox, and summer solstice during three different years, 2015, 2017, and 2020, with different solar activities. The models, along with ionospheric physical data, were used for the daily prediction of ionospheric scintillations for the consequent day after the modeling. The prediction results were evaluated using S4 derived from GNSS observations at GUAM station. The designed model has the ability to predict daily ionospheric scintillations with an accuracy of about 81% for the S4 and about 80% for the ROTI.

Global Distribution of Nighttime MSTIDs and Its Association With E Region Irregularities Seen by CHAMP Satellite

AbstractWe investigate the correlation of sporadic E (Es) with the occurrence of medium‐scale traveling ionospheric disturbances (MSTIDs) at night in middle latitudes (25°–40°N and 25°–40°S magnetic latitudes) by examining their occurrence climatology. The occurrence climatology of Es and MSTIDs is derived using the Challenging Minisatellite Payload satellite data acquired in 2001–2008 and 2001–2009, respectively. Electron density irregularities and radio scintillations are used as the detection proxies of MSTIDs and Es, respectively. The occurrence rate of MSTIDs shows a semi‐annual variation with the primary peak during June solstices and the secondary peak during December solstices in both hemispheres. However, the occurrence rate of Es shows a seasonal variation with a pronounced peak in summer in both hemispheres. The occurrence of MSTIDs during local summer and equinoxes is correlated with the occurrence of local Es, but the high occurrence rate of MSTIDs in local winter is not correlated with local winter hemisphere Es. MSTIDs in the winter hemisphere are correlated with magnetically conjugate MSTIDs in the summer hemisphere; these summer hemisphere MSTIDs are correlated with the occurrence of Es in the summer hemisphere. The occurrence rate of MSTIDs clearly shows an increase with decreasing solar activity, but the solar cycle dependence of Es is not obvious from the data. This observation suggests that the generation of MSTIDs is significantly affected by factors other than Es such as the growth rate of the Perkins instability, atmospheric gravity waves, and the F region conductance.