Medium-scale Traveling Ionospheric Disturbances Research Articles

Interaction of Oppositely Traveling Medium‐Scale Traveling Ionospheric Disturbances Observed in Low Latitudes During Geomagnetically Quiet Nighttime

AbstractIn this study, an unusual event of medium‐scale traveling ionospheric disturbances (MSTIDs) that propagated in opposite directions was observed by multi‐instruments (all‐sky imager, global positioning system (GPS), and digisonde) in low latitudes during geomagnetically quiet nighttime. These MSTIDs had wavefronts aligned from northwest to southeast. One MSTID propagated southwestward and another propagated northeastward. They encountered and interacted with each other. Some MSTIDs structures merged into one and disappeared after the interaction. Furthermore, an eastward moving plasma bubble also encountered the MSTIDs and then gradually dissipated during the propagation process. The MSTIDs traveling in opposite directions should be related to ionospheric plasma motion and their trigger mechanisms. The interactive process of MSTIDS involved in plasma drifts and polarization electric fields. Meanwhile, the interaction with an ionospheric irregularity structure can change some of the MSTID characteristics.

Solar activity dependence of medium-scale traveling ionospheric disturbances using GPS receivers in Japan

In order to reveal solar activity dependence of the medium-scale traveling ionospheric disturbances (MSTIDs) at midlatitudes, total electron content (TEC) data obtained from a Global Positioning System (GPS) receiver network in Japan during 22 years from 1998 to 2019 were analyzed. We have calculated the detrended TEC by subtracting the 1-h running average from the original TEC data for each satellite and receiver pair, and made two-dimensional TEC maps of the detrended TEC with a spatial resolution of 0.15° × 0.15° in longitude and latitude. We have investigated MSTID activity, defined as delta I/overline{I}, where delta I and overline{I} are standard deviation of the detrended TEC and the average vertical TEC within the area of 133.0°–137.0° E and 33.0°–37.0° N for 1 h, respectively. From each 2-h time series of the detrended TEC data within the same area as the MSTID activity, auto-correlation functions (ACFs) of the detrended TEC were calculated to estimate the horizontal propagation velocity and direction of the MSTIDs. Statistical results of the MSTID activity and propagation direction of MSTIDs were consistent with previous studies and support the idea that daytime MSTIDs could be caused by atmospheric gravity waves, and that nighttime MSTIDs were caused by electro-dynamical forces, such as the Perkins instability. From the current long-term observations, we have found that the nighttime MSTID activity and occurrence rate increased with decreasing solar activity. For the daytime MSTID, the occurrence rate increased with decreasing solar activity, whereas the MSTID activity did not show distinct solar activity dependence. These results suggest that the secondary gravity waves generated by dissipation of the primary gravity waves propagating from below increase under low solar activity conditions. The mean horizontal phase velocity of the MSTIDs during nighttime did not show a distinct solar activity dependence, whereas that during daytime showed an anticorrelation with solar activity. The horizontal phase velocity of the daytime MSTIDs was widely distributed from 40 to 180 m/s under high solar activity conditions, whereas it ranged between 80 and 200 m/s, with a maximum occurrence at 130 m/s under low solar activity conditions, suggesting that gravity waves with low phase velocity could be dissipated by high viscosity in the thermosphere under low solar activity conditions.

Study of Medium Scale Travelling Ionospheric Disturbances Using Navic Signals

The Medium Scale Travelling Ionospheric Disturbances (MSTIDs) are the most commonly occurring irregularity phenomena in the F region of the ionosphere. MSTIDs appear as oscillating wavelike disturbances and can be observed as the temporal and spatial fluctuations in the ionospheric Total Electron Content (TEC). In this paper we determine the TEC by observing the carrier phase at L5 and S-band frequencies from a geostationary satellite of the Indian Regional Navigation Satellite System (IRNSS) constellation,also known as Navigation with Indian Constellation (NavIC). The TEC so determined exhibits a broad diurnal variation, superimposed on which the temporal fluctuations due to MSTIDs manifest themselves. We have used a network of three such stations to study the horizontal propagation of the MSTIDs. We present, for the first time preliminary results of the TID occurrences and their characteristics, such as – period, amplitude and horizontal phase velocity,obtained using NavIC signals for a low latitude station Bangalore (12.90°N, 77.36°E).

Equatorial Plasma Bubbles and Medium-Scale Traveling Ionospheric Disturbance Interaction Observed by OI 630 nm airglow imaging at Bom Jesus de Lapa, Brazil

OI 630.0 nm airglow observations, from a new observatory at Bom Jesus de Lapa, were used to study the interaction between EPBs (Equatorial Plasma Bubbles) and the MSTID (Medium-Scale Traveling Ionospheric Disturbance) over the Northeast region in Brazil. On the night of September 16 to 17, 2020, an EPB was observed propagating eastward, in an apparent fossil stage, until it interacted with a dark band electrified MSTID (eMSTID). After the interaction, four EPBs merged, followed by an abrupt southward development and bifurcations. Analysis of the data suggests that an eastward polarization electric field, induced by the dark band eMSTID, forced the EPB into an upward drift, growing latitudinally along the magnetic field lines and then bifurcating.

Review of ionospheric irregularities and ionospheric electrodynamic coupling in the middle latitude region

This paper briefly reviews ionospheric irregularities that occur in the E and F regions at mid-latitudes. Sporadic E (ES) is a common ionospheric irregularity phenomenon that is first noticed in the E layer. ES mainly appears during daytime in summer hemispheres, and is formed primarily from neutral wind shear in the mesosphere and lower thermosphere (MLT) region. Field-aligned irregularity (FAI) in the E region is also observed by Very High Frequency (VHF) radar in mid-latitude regions. FAI frequently occurs after sunset in summer hemispheres, and spectrum features of E region FAI echoes suggest that type-2 irregularity is dominant in the nighttime ionosphere. A close relationship between ES and E region FAI implies that ES may be a possible source of E region FAI in the nighttime ionosphere. Strong neutral wind shear, steep ES plasma density gradient, and a polarized electric field are the significant factors affecting the formation of E region FAI. At mid-latitudes, joint observational experiments including ionosonde, VHF radar, Global Positioning System (GPS) stations, and all-sky optical images have revealed strong connections across different scales of ionospheric irregularities in the nighttime F region, such as spread F (SF), medium-scale traveling ionospheric disturbances (MSTID), and F region FAI. Observations suggest that different scales of ionospheric irregularities are generally attributed to the Perkins instability and subsequently excited gradient drift instability. Nighttime MSTID can further evolve into small-scale structures through a nonlinear cascade process when a steep plasma density gradient exists at the bottom of the F region. In addition, the effect of ionospheric electrodynamic coupling processes, including ionospheric E-F coupling and inter-hemispheric coupling on the generation of ionospheric irregularities, becomes more prominent due to the significant dip angle and equipotentiality of magnetic field lines in the mid-latitude ionosphere. Polarized electric fields can map to different ionospheric regions and excite plasma instabilities which form ionospheric irregularities. Nevertheless, the mapping efficiency of a polarized electric field depends on the ionospheric background and spatial scale of the field.

Multi-instrument observations of SCIPS: 1. ISR and GPS TEC results

An uninterrupted multi-day (6–8 May 2013) ionospheric F-region event with features indicative of medium-scale traveling ionospheric disturbances (MSTIDs) was detected with the Millstone Hill (MH) incoherent scatter radar (ISR). It was later identified, with the addition of Global Positioning System total electron content (GPS-TEC) imaging, as a novel ionospheric phenomenon. This phenomenon is herein termed semi-coherent ionospheric pulsing structures (SCIPS). The presumptive-MSTIDs in this multi-day event had a ~1 h period and were observed during calm-to-minor geomagnetic conditions using both the vertical-looking (Zenith) and steerable (Millstone Hill Steerable Antenna, or MISA) MH ISR systems. To image the MH MSTID events on a larger horizontal scale than is possible with ISR systems alone, a dense network of GPS TEC receivers was leveraged. The ISR-observed event was located in the GPS-TEC data geographically centered on the MH location with a ~100 km resolution (pixel size). However, keogram analysis of the GPS-TEC data revealed that the event had coherency across the continental United States. The same technique additionally exposed similar events occurring globally throughout the observing period. Our multi-instrument approach allows us to conclude that the event was comprised of large-scale and continuously forced, semi-coherent ionospheric pulsing structures (SCIPS) that masqueraded as MSTIDs when viewed locally. The GPS-TEC images show that the SCIPS were stationary in longitude on a global scale, but appeared to propagate in a southward direction in the Northern Hemisphere. It was not possible to obtain direct imaging in the southern hemisphere due to the smaller number of receivers. The SCIPS appear to originate at high latitudes and, in several instances, were coherent across over 10,000 km. The apparent high latitude source location, ubiquity, and large-scale coherence of the SCIPS suggest unexpected impulsive auroral oval sources containing enough energy to continually force the observed MSTID-like structures even during low geomagnetic activity periods.

Characteristics of Medium-Scale Traveling Ionospheric Disturbances and Ionospheric Irregularities at Mid-Latitudes Revealed by the Total Electron Content Associated With the Beidou Geostationary Satellite

In this study, we characterized the variations in ionospheric irregularities and medium-scale traveling ionospheric disturbances (MSTIDs) simultaneously at mid-latitudes over central China based on high-fidelity observations of the total electron content (TEC) from a Beidou geostationary satellite and explored their quantitative relationships during 2016–2017. Ionospheric irregularities generally occurred during 20:00–03:00 local time (LT) in summer and reached a peak rate of ~30% at night; during the daytime in summer, the irregularities had a weak occurrence peak of not more than ~10%. The occurrence rate of nighttime MSTIDs showed a major peak of ~45% in summer and a secondary peak of ~20% in winter, whereas the main peak in winter was ~30% during the daytime. Additionally, the period, velocity, wavelength, and propagation direction of nighttime MSTIDs were different from those of daytime MSTIDs. There was a strong correlation between ionospheric irregularities and MSTIDs at night when the rate of ionospheric irregularities occurring during MSTIDs reached 90%. However, the situation during the daytime was different; the rate of ionospheric irregularities associated with MSTIDs did not exceed ~20%. These results indicate that nighttime MSTIDs could play an important role in producing ionospheric irregularities, but daytime MSTIDs do not. The different diurnal relationships between ionospheric irregularities and MSTIDs can be attributed to the different generation processes of MSTIDs. Our results from Beidou GEO TEC observations provide a new perspective for understanding ionospheric irregularities and MSTIDs and their quantitative relationships.

Interaction Between a Southwestward Propagating MSTID and a Poleward Moving WSA‐Like Plasma Patch on a Magnetically Quiet Night at Midlatitude China Region

AbstractIn this paper, we first investigate the effects of a postevening Weddell Sea Anomaly (WSA)‐like plasma patch on a southwestward propagating medium‐scale traveling ionospheric disturbance (MSTID) over Xinglong, China (40.4°N, 117.6°E; Mlat. ~30.4°N). We found that some of this kind of WSA‐like plasma patches moved northward from the equatorial ionization anomaly (EIA) regions to midlatitudes, as they traveled westward into China. During 2012–2016, these plasma patches frequently occurred during the period of May–August with a monthly occurrence rate of over 20%, causing nighttime plasma density enhancements (NPDEs) in midlatitudes of China. Over 50% of these structures were accompanied by concurrent MSTID and Es. We propose that an intense polarization electric field (PEF) associated with an MSTID/Es from the more northern regions of EIA could frequently drive these plasma patches poleward. On the night of 27 June 2014 (Kp < 2−), either an MSTID and an intense Es layer (the maximum foEs >12 MHz) occurred at the onset of the poleward motion of a WSA‐like plasma patch, lending credence to this possibility. The observed plasma patch was pushed poleward to interact with the observed MSTID, causing some poleward extending C‐shaped airglow depletions/enhancements of the MSTID in a transition region where the ionosphere changed from a collapse region to an uplifted one. We attributed those poleward extending airglow depletions to the interaction between the MSTID and the plasma patch because of the secondary gradient drift instability and those of airglow enhancements to the redistribution of plasma.

Equatorial Plasma Bubble Occurrence Under Propagation of MSTID and MLT Gravity Waves

AbstractWe observed a signature of equatorial plasma bubbles (EPBs) followed by a medium‐scale traveling ionospheric disturbance (MSTID) crossing the solar terminator over the geomagnetic equator during the period of post‐sunset rise (PSSR) of the F layer. Simultaneous observations of the EPBs and the MSTIDs by ground‐based Global Navigation Satellite System receivers and OI 630‐nm imagers, ionospheric parameters by ionosondes, and mesosphere–lower thermosphere (MLT) gravity waves (MLT‐GWs) by OH airglow imagers have been carried out in the equatorial and low‐latitude region of Brazil. On 16–17 September 2015, MSTIDs with very fast horizontal phase speeds, propagating toward northeast (NE), were observed over the latitude region of 0–30°S in the afternoon to evening time zone. It was geomagnetically quiet time (Kp: 2–3). An EPB development was observed after one of the MSTIDs crossed the solar terminator at 22:00 UT. Large‐scale MLT‐GWs with slower phase speeds were also observed both at São João do Cariri (7.5°S, 35.0°W) propagating from southwest (SW) to NE and Cachoeira Paulista (22.7°S, 45.0°W) propagating northward. This is to report on what we consider as a signature of direct seeding of EPBs by an MSTID that was likely induced by a secondary GW from tropospheric deep cloud convections to the south. This study highlights a possible dynamical process from the troposphere to ionosphere via this vertical coupling process over the 2,500 km of horizontal distance.

Estimation of frequency and duration of ionospheric disturbances over Turkey with IONOLAB-FFT algorithm

One of the more common methods of observation of variability of the Earth’s ionosphere is based on total electron content (TEC) estimated from ground-based dual-frequency Global Positioning System (GPS) receivers. Variations in solar, geomagnetic and seismic activity cause depletions or enhancements in the ionospheric electron concentrations that can be detected as disturbances. Some of these disturbances have wave-like characteristics, where frequency of oscillation can be used to identify and classify the disturbance. In this study, the frequency of such periodic disturbances is estimated using a fast Fourier transform (FFT)-based method, namely IONOLAB-FFT, in the spectral domain. IONOLAB-FFT, which was initially developed to be used on slant TEC (STEC), is modified to be applied to TEC in the local zenith direction of the receiver. The algorithm is tested using literature data on disturbances generated by a geomagnetic activity, a solar flare, a medium-scale traveling ionospheric disturbance (MSTID), a large-scale TID (LSTID) and an earthquake. An accordance with these known disturbances is observed in running IONOLAB-FFT, and the main frequencies and durations of the disturbances are estimated. IONOLAB-FFT method is applied to TEC computed from Turkish Permanent GPS Network (TNPGN-Active) which lies in mid-latitude region to detect the any wave-like oscillations, sudden disturbances and other irregularities during December, March, June and September months for 2010, 2011 and 2012 years. It is observed that a large number of the estimated frequencies are accumulated between 0.08 and 0.14 MHz corresponding to periods of 3.5 h to 2 h. The significant frequencies are grouped less than 0.28 MHz. A large number of the durations of the oscillations are between 425 and 550 min in 2010, 300 and 550 min in 2011 and 350 and 400 min in 2012. The longest duration (around 800 min: 13.33 h) is observed in December months, and the shortest duration (around 2 h) is observed in September months.

Spatial Characteristics on the Occurrence of the Nighttime Midlatitude Medium‐Scale Traveling Ionospheric Disturbance at Topside Ionosphere Revealed by the Swarm Satellite

AbstractUsing 6 years collecting of electron density (Ne) data from the Swarm A satellite, this study portrays comprehensive maps of the occurrence of medium‐scale traveling ionospheric disturbance (MSTID) at middle latitudes, which is characterized by the in situ absolute Ne fluctuations above a certain threshold. Two interesting spatial preferences on the occurrence of MSTID as well as their dependence on local time and solar cycle are captured, that is, (1) regional preference near Weddell Sea Anomaly (WSA) to its west during December solstice, MSTID in this region appears even at very low latitudes (at least to 10°N in magnetic latitude) and (2) preference at middle latitudes with a wide zonal extension, which is similar to the recently disclosed nighttime midlatitude plasma band‐like enhancement (NMPBE) of the background plasma density (Zhong et al., 2019, https://doi.org/10.1029/2018JA026059). The first preference of MSTID occurring near WSA region can be understood as the effects of horizontal neutral wind contribution to the Perkins instability, with the principal requirement of sporadic E occurrence via ionospheric E‐F region coupling. The fundamental mechanism of the second preference of MSTID occurring includes the interhemispheric coupling that the MSTID can also develop in the winter hemisphere where the local growth rate of Perkins instability is low. Besides, the presence of NMPBE during low solar activity years sets up a favorable environment for the appearance of MSTID with considerable fluctuation amplitude.

Coupling Between E Region Quasi‐Periodic Echoes and F Region Medium‐Scale Traveling Ionospheric Disturbances at Low Latitudes

AbstractE region quasi‐periodic (QP) echoes from a VHF coherent backscatter radar, sporadic E (Es) layer from a digisonde, and F region medium‐scale traveling ionospheric disturbances (MSTIDs) from global navigation satellite systems receivers were simultaneously observed at low latitudes. The results on the night of 3 March 2018 show that the QP echoes in radar height‐time intensity maps were clustered into groups, coinciding with the periods of MSTIDs and strong Es layer. The MSTIDs had phase fronts elongating in the northwest‐southeast direction and propagated southwestward from middle to low latitudes. Similar to the propagation direction of MSTIDs, the low‐latitude Es layers also propagated southwestward. For the QP echoing clusters, a westward drift was seen from the radar multibeam observations. The Doppler velocities of QP echoes show beam dependence, with significantly enhanced positive values (motion away from the radar) in the westernmost beam. Based on a preliminary statistical analysis during the period March–June 2018, it was found that out of a total of 102 nights, there are 32 nights when QP echoes were generated. The simultaneous occurrences of QP echoes and MSTIDs were observed on six nights. We suggest that when the MSTIDs coming from middle latitudes approach low latitudes, the polarization electric fields associated with the MSTIDs could modulate the E region plasma instability producing QP echoes at low latitudes through the E‐F region electrodynamic coupling.

The Persistent Ionospheric Responses Over Japan After the Impact of the 2011 Tohoku Earthquake

AbstractIn this study, we report the persistent impacts of the 2011 Tohoku earthquake/tsunami on the ionosphere using the ground‐based Global Navigation Satellite System and FORMOSAT‐3/COSMIC total electron content. Multiple unusual ionospheric phenomena, such as ionospheric irregularities, nighttime medium‐scale traveling ionospheric disturbances (MSTIDs), and planar traveling ionospheric disturbances (TIDs), were observed after the emergence of tsunami‐induced concentric gravity waves. The ionospheric irregularities initially developed over the Hokkaido region following the interference of gravity waves at ~8:45 UT. Remarkably, the Perkins‐type nighttime MSTIDs accompanying the planar TIDs were discernible over Japan following the irregularities. By comparing with the tsunami model simulation and ocean buoy observations, it is determined that these planar TIDs, lasting for about 10 hr, were likely related to tsunami ocean waves reflected by seamounts, ridges, islands, and seafloor topography in the Pacific Ocean. Due to the absence of sporadic E layers, we suggest that the coupling between the tsunami‐generated gravity waves and the Perkins instability plays an essential role in initiating the equinoctial nighttime MSTIDs. The long‐lasting tsunami can continuously impact the ionosphere, affecting the nighttime ionospheric electrodynamics and making the conditions conducive for the development of midlatitude nighttime ionospheric irregularities and instabilities.

Multievent Analysis of Oscillatory Motion of Medium‐Scale Traveling Ionospheric Disturbances Observed by a 630‐nm Airglow Imager Over Tromsø

AbstractWe present a comprehensive investigation on the propagation characteristics of duskside medium‐scale traveling ionospheric disturbances (MSTIDs) using 630.0‐nm airglow emissions over Tromsø (69.6°N, 19.2°E; magnetic latitude: 66.7°N). The unique points of our observation are (1) duskside MSTIDs primarily exhibited eastward motion under quiet conditions but turned to the westward direction associated with geomagnetic disturbances, (2) the westward moving MSTIDs again turned to the eastward direction when the geomagnetic disturbance ceased, (3) the turning of MSTIDs to the westward direction was invariably associated with an increase of the northward component of the magnetic field observed by the local ground‐based magnetometers and with the equatorward expansion of the auroral oval, and (4) the Super Dual Auroral Radar Network convection maps revealed that the location of Tromsø was inside (outside) the duskside convection cell during the time of appearance of westward (eastward) moving MSTIDs. The average eastward and westward velocities of MSTIDs were ~25–80 and ~40–140 m/s, respectively. The Doppler shift measurement of the 630‐nm airglow by a Fabry‐Perot interferometer at Tromsø showed that northeastward winds were predominant during the appearance of eastward moving MSTIDs. These experimental evidences suggest that the oscillatory motion of MSTIDs over high latitudes is driven by the convection electric field. The MSTIDs tend to move eastward under geomagnetically quiet conditions but show westward motion under the influence of convection electric field associated with auroral activities in the duskside of two‐cell convection pattern.

Wavenumber Spectra of Atmospheric Gravity Waves and Medium‐Scale Traveling Ionospheric Disturbances Based on More Than 10‐Year Airglow Images in Japan, Russia, and Canada

AbstractWe have studied atmospheric gravity waves (AGWs) and nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) by applying three‐dimensional spectral analysis technique to 557.7‐ and 630.0‐nm airglow images at Shigaraki (SGK) (35°N, 136°E, 1999–2017) and Rikubetsu (RIK) (44°N, 144°E, 1999–2017), Japan, Athabasca (ATH), Canada, (55°N, 247°E, 2005–2017), and Magadan (MGD), Russia (60°N, 151°E, 2008–2017), focusing on their horizontal wavenumber spectra. For the AGWs in 557.7‐nm images, the power spectra in summer are stronger than in other seasons, probably due to stronger tropospheric convection. The highest energy content of the waves are mostly at wavelengths between 20 and 300 km at MGD, ATH, and RIK, while it is above 200 km at SGK. The largest power spectral density is obtained at RIK at wavelengths of 30–100 km and then ATH. The slopes of the horizontal wavenumber spectra varies from −2.77 to −3.22. From the MSTIDs in 630.0‐nm images, the power spectra in summer at RIK and SGK are stronger than those in other seasons regardless of solar activity. The power spectra in solar quiet time are stronger than those in solar active time at all four stations. These features can be explained by the Perkins instability with coupling between sporadic E and F layers. The spectral slope decreases with increasing latitudes. Weak positive correlations were obtained between the daily wave power of AGWs in 557.7‐nm images and MSTIDs in 630.0‐nm images, suggesting that the MSTIDs in the thermosphere may be partially generated by the AGWs from the mesopause region.

Understanding Inter-Hemispheric Traveling Ionospheric Disturbances and Their Mechanisms

Traveling ionospheric disturbances (TIDs) are wave-like disturbances in ionospheric plasma density. They are often observed during both quiet (medium-scale TID) and geomagnetically disturbed (large-scale TID) conditions. Their amplitudes can reach double-digit percentages of the background plasma density, and their existence presents a challenge for accurate ionosphere specification. In this study, we examine TID properties using observations obtained during two geomagnetically disturbed periods using multiple ground and space-borne instruments, such as magnetometers, Global Navigation Satellite System (GNSS) receivers, and the SWARM satellite. Reference quiet time observations are also provided for both storms. We use a thermosphere–ionosphere–electrodynamics general circulation model (TIEGCM) results to properly interpret TID features and their drivers. This combination of observations and modeling allows the investigation of variations of TID generation mechanisms and subsequent wave propagation, particularly as a function of different plasma background densities during various geophysical conditions. The trans-equatorial coupling of TIDs in the northern and southern hemispheres is also investigated with respect to attenuation and propagation characteristics. We show that TID properties during trans-equatorial events may be substantially affected by storm time background neutral wind perturbation.

Impact of medium-scale traveling ionospheric disturbances on network real-time kinematic services: CATNET study case

Medium-scale traveling ionospheric disturbances (MSTIDs) are fluctuations in the plasma density that propagate through the upper layer of the atmosphere at velocities of approximately 100 m/s and periods reaching some tens of minutes. Due to their wavelengths, MSTIDs can degrade the performance of differential positioning techniques, such as real-time kinematics (RTK) or network-RTK (NRTK). This paper defines a novel methodology as a tool for relating the errors in NRTK positioning based on an MSTIDs indicator using the second difference in time of the slant total electron content (STEC). The proposed methodology performs integer ambiguity resolution (IAR) on the undifferenced measurements instead of using double-differenced carrier-phase measurements, as it is usual in RTK and NRTK. Statistical tests are applied to evaluate the degradation in the position errors caused by the impacts of MSTIDs on RTK and NRTK positioning over a data set spanning one year gathered from the CATNET network; a dual-frequency network of fixed permanent GNSS receivers located at the mid-latitudes of northeastern Spain. With the development of the proposed methodology for measuring the position degradation, another results of the present research are the establishment of thresholds for the proposed MSTIDs index, which can be used to monitor the positioning solution and to warn users when the measurements are affected by MSTIDs events, relating the position error to MSTIDs that affect not only the user receivers but also of the reference receivers within the network.

An overview of methodologies for real-time detection, characterisation and tracking of traveling ionospheric disturbances developed in the TechTIDE project

The main objective of the TechTIDE project (warning and mitigation technologies for travelling ionospheric disturbances effects) is the development of an identification and tracking system for travelling ionospheric disturbances (TIDs) which will issue warnings of electron density perturbations over large world regions. The TechTIDE project has put in operation a real-time warning system that provides the results of complementary TID detection methodologies and many potential drivers to help users assess the risks and develop mitigation techniques tailored to their applications. The TechTIDE methodologies are able to detect in real time activity caused by both large-scale and medium-scale TIDs and characterize background conditions and external drivers, as an additional information required by the users to assess the criticality of the ongoing disturbances in real time. TechTIDE methodologies are based on the exploitation of data collected in real time from Digisondes, Global Navigation Satellite System (GNSS) receivers and Continuous Doppler Sounding System (CDSS) networks. The results are obtained and provided to users in real time. The paper presents the achievements of the project and discusses the challenges faced in the development of the final TechTIDE warning system.

Propagation of Nighttime Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) During High and Low Solar-Activity Conditions

Propagation of Nighttime Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) During High and Low Solar-Activity Conditions

Залежність просторового періоду рухомих іоносферних збурень від їхньої відносної амплітуди

The relationship between the horizontal spatial period L and the relative amplitude Ad of traveling ionospheric disturbances (TID) at various levels of solar (SA) and geomagnetic (GA) activity is experimentally studied. In the vast majority of cases, the TIDs observed during our study were generated by high-latitude sources. It was found that the period L and amplitude Ad of the medium-scale (MS) TIDs (L = 100 – 800 km) are related by a linear dependence, which does not depend upon the SA level. For large-scale (LS) TID with L = 1000 – 4000 km, the linear approximation of the function L(Ad) at low and high SA levels are increasing or decreasing functions, respectively. For global-scale (GM) TIDs with L = 5000 – 35000 km at low SA levels, the linear approximation L(Ad) is an increasing function. The function L(Ad) for TIDs of all spatial scales does not depend upon the GA level. The data were collected at the radio-physical observatory of V. N. Karazin Kharkiv National University (j = 49.63°N, l = 36.32°E) in 1999—2010 with the ionosphere radio sounding by using coherent radio waves at frequencies of about 150 and 400 MHz radiated by low-orbit navigation satellites Parus and Cicada orbiting at circular near-polar orbit with a height of about 1000 km. The experimental dependence of the horizontal period L of TID upon their relative amplitude Ad is explained based on the global prognostic semi-empirical model of the generation and propagation of acoustic-gravitational waves and traveling ionospheric disturbances.