Ionospheric Disturbances Research Articles

A Tropical Cyclone or Typhoon as an Element of the Earth–Atmosphere–Ionosphere–Magnetosphere System: Theory, Simulations, and Observations

The premise has been validated that a tropical cyclone (TC, typhoon, hurricane), one of the most powerful large-scale formations systematically arising in the atmosphere, is an element of the ocean–atmosphere–ionosphere–magnetosphere system. The TC plays a crucial role with regard to a global-scale mass and energy exchange in this system. The study of this system encompasses a broad spectrum of physical phenomena occurring and processes operating within the system components, as well as the mechanisms of their interactions. The problem under discussion pertains to interdisciplinary science. Its scope ranges from different Earth sciences to geospace sciences, which comprise the physics of the ocean, meteorology, the physics of the Earth’s atmospheric and space environment, etc. Observations of the ionospheric response to the impact of a number of unique typhoons made using multifrequency multiple path oblique incidence ionospheric sounding have confirmed the definitive role that the internal gravity waves and infrasound play in producing atmospheric–ionospheric disturbances. It has been demonstrated that these disturbances are capable of significantly affecting the characteristics of high-frequency radio waves.

Periodic oscillations of Doppler frequency excited by the traveling ionospheric disturbances associated with the Tonga eruption in 2022

The explosive eruption of the Hunga Tonga-Hunga Ha’apai volcano on 15 January 2022 generated atmospheric waves traveling around the Earth, which caused ionospheric disturbances on various spatio-temporal scales. A HF Doppler sounding system in Japan detected characteristic ionospheric disturbances showing periodic oscillations in the Doppler frequency with a period of ~ 4 min. In this study, such periodic oscillations were examined by comparing Doppler frequency data with Total Electron Content data obtained by Global Navigation Satellite System. The observed periodic oscillations in the Doppler frequency were characterized by a sawtooth or S-letter shaped variation, implying the passage of the traveling ionospheric disturbances through the reflection points of the HF Doppler sounding system. It was also found that the periodic oscillations occurred prior to the arrival of the tropospheric Lamb wave excited by the Tonga eruption. From the total electron content data, the traveling ionospheric disturbances causing the periodic oscillations were excited by the tropospheric Lamb waves at the conjugate point in the southern hemisphere, namely, the electric field perturbations due to the Lamb waves in the southern hemisphere mapped onto the sensing area of the HF Doppler sounding system in the northern hemisphere along the magnetic field lines. The periodic oscillations were observed only in the path between Chofu transmitter and Sarobetsu receiver, whose the radio propagation path is almost aligned in the north–south direction. This suggests that the traveling ionospheric disturbance has a structure elongating in the meridional direction. The variation in the Doppler frequency was reproduced by using a simple model of the propagation of the traveling ionospheric disturbances and the resultant motion of the reflection point. As a result, the vertical motion of the reflection point associated with the periodic oscillations was estimated to be about 1 km. It is known that 4-min period variations are sometimes observed in association with earthquakes, which is due to resonances of acoustic mode waves propagating between the ground and the lower ionosphere. Therefore, a similar resonance structure in the southern hemisphere is a plausible source of the traveling ionospheric disturbances detected in the northern hemisphere.Graphical

Using real GNSS data for ionospheric disturbance remote sensing associated with strong thunderstorm over Wuhan city

Using real GNSS data for ionospheric disturbance remote sensing associated with strong thunderstorm over Wuhan city

The method of GPS monitoring of small-scale inhomogeneities of the ionosphere and its application for predicting the noise immunity of satellite communication systems

A method has been developed for GPS monitoring of small-scale fluctuations in the total electronic content of the ionosphere and using its results to predict changes in the noise immunity of satellite communication systems under ionospheric disturbances. To this end, the software of the GPStation-6 receiver of the global navigation satellite system was modified in the direction of replacing the code measurements of the total electronic content of the ionosphere with combined (code-phase) measurements, which practically eliminates the "noise" component of the measurement error. To separate small-scale fluctuations of the total electronic content from large-scale ones, it is proposed to use a 6th-order digital Butterworth filter, which in the transmission frequency range (1-10 Hz) at a sampling frequency of 50 Hz provides an amplitude-frequency response close to ideal and introduces a delay not exceeding the permissible value. An expression is obtained for calculating the output samples of this digital filter. The obtained results of estimating small-scale fluctuations of the total electron content of the ionosphere at the output of the digital filter allow us to estimate the standard deviation of these fluctuations. On this basis, the results of calculating the ionospheric flicker index of the received signals of satellite communication systems are obtained. This makes it possible to predict the probability of their erroneous reception at a given average value of the signal-to-noise ratio at the input of the satellite receiver. Analysis of the obtained results of predicting the noise immunity of satellite communication systems shows that in the conditions of an undisturbed mid-latitude ionosphere, the probability of erroneous reception may exceed the permissible value for 30 seconds. This confirms the assumption that with small-scale disturbances of the ionosphere, the probability of error in satellite communication systems may exceed the permissible value for a long time.

Studying the Fixing Rate of GPS PPP Ambiguity Resolution Under Different Geomagnetic Storm Intensities

AbstractGlobal Positioning System (GPS) Precise Point Positioning (PPP) with correct fixing ambiguity resolution (AR) can reach cm‐mm level positioning accuracy. However, this accuracy can be degraded by the geomagnetic storm effects. To comprehensively investigate the ambiguity resolved percentage (ARP) of GPS kinematic PPP, referred to as PPP‐ARP, under different intensities of geomagnetic storms, based on the Natural Resources Canada's Canadian Spatial Reference System (CSRS) PPP, this study for the first time gives the correlation between the PPP‐ARP and storm intensity using 67 storms occurred in the past 5 years of 2018–2022. Experimental results indicate that the PPP‐ARP decreases gradually as the increase of geomagnetic storm intensity. Under quiet and low geomagnetic conditions (Dstmin > −50 nT), the PPP‐ARP of global GNSS stations can achieve more than 96%, while these during strong storms (Dstmin ≤ −100 nT) are generally lower than 90.0%, especially for the PPP‐ARP of some stations located at low latitudes which are lower than 40.0%. The mechanism of PPP‐ARP decrease under geomagnetic storms is mainly due to the cycle slips and even loss of lock of GNSS signals caused by the storms induced ionospheric disturbances and scintillations. In addition, different from many previous studies, we found that the CSRS‐PPP with AR can achieve good positioning accuracy (3D RMS <0.2 m) even under strong geomagnetic storms.

Secondary Gravity Waves From the Tonga Volcano Eruption: Observation and Modeling Over New Zealand and Australia

AbstractThe biggest volcanic eruption since 1991 happened on 15 January 2022 on the island of Hunga Tonga‐Hunga Haʻapai (20.6°S; 175.4°W) in the South Pacific between 4:00 and 4:16 UT. The updrafts from the eruption reached 58 km height. In order to observe its ionospheric effects, approximately 750 GNSS receivers in New Zealand and Australia were used to calculate the detrended total electron content (dTEC). Traveling ionospheric disturbances (TIDs) were observed over New Zealand 1.0–1.5 hr after the volcano eruption, with a horizontal wavelength () of 1,525 km, horizontal phase velocity () of 635 m/s, period (τ) of 40 min, and azimuth (α) of 214°. On the other hand, TIDs were observed 2–3 hr after the eruption in Australia with , , τ, and α of 922 km, 375 m/s, 41 min, and 266°, respectively. Using reverse ray tracing, we found that these GWs originated at z > 100 km at a location ∼500 km south of Tonga, in agreement with model results for the location of a large amplitude body force created from the breaking of primary GWs from the eruption. Thus, we found that these fast GWs were secondary, not primary GWs from the Tonga eruption.

Daytime Medium Scale Traveling Ionospheric Disturbances (MSTIDS) Over the Andes Mountains at Equatorial and Low Magnetic Latitudes

AbstractWe analyze daytime quiet‐time MSTIDs between 2013 and 2015 at the geomagnetic equatorial and low latitude regions of the Chilean and Argentinian Andes using keograms of detrended total electron content (dTEC). The MSTIDs had a higher occurrence rate at geomagnetic equatorial latitudes in the June solstice (winter) and spring (SON). The propagation directions changed with the season: summer (DJF) [southeast, south, southwest, and west], winter (JJA) [north and northeast], and equinoxes [north, northeast, south, southwest, and west]. In addition, the MSTIDs at low latitudes observed between 8:00 and 12:00 UT occur more often during the December solstice and propagate northwestward and northeastward. After 12:00 UT, they are mostly observed in the equinoxes and June solstice. Their predominant propagation directions depend on the season: summer (all directions with a preference for northeastward), autumn (MAM) [north and northeast], winter (north and northeast), and spring (north, northeast, and southwest). The MSTID propagation direction at different latitudes was explained by the location of the possible sources. Besides, we calculated MSTIDs parameters at geomagnetic low latitudes over the Andes Mountains and compared them with those estimated at the geomagnetic equatorial latitudes. We found that the former is smaller on average than the latter. Also, our observations validate recent model results obtained during geomagnetically quiet‐time as well as daytime MSTIDs during winter over the south of South America. These results suggest that secondary or high‐order gravity waves (GWs) from orographic forcing are the most likely source of these MSTIDs.

Geomagnetic Storm Associated D‐Region Anomalies Estimated From VLF Observations at a Low‐Latitude Station, Suva, Fiji

AbstractA comprehensive analysis of subionospheric Very Low Frequency (VLF) signals from transmitters with call‐signs NWC, NPM, and NLK monitored at a low‐latitude station, Suva, Fiji, has been carried out to determine the D‐region effects of the intense geomagnetic storms for a period of 7 years (2011–2016 and 2018). The periods of 2011–2016 and 2018 fall under the 24th solar cycle with yearly mean sunspot numbers 80.8–39.8 and 7.0, respectively. Seven out of 12 geomagnetic storms revealed VLF anomalies during the storm main phase day and storm recovery phase days. A pronounced decrease in the VLF amplitude and phase for the storms having main phase onset in the nighttime was found. Out of seven geomagnetic storms, a storm of St Patrick's Day of 17–18 March 2013 is presented as a case study and the same analysis was done for all the storms. The anomalies in the VLF amplitude and phase have been modeled using Long‐Wave Propagation Capability code V2.1 to obtain the changes in Wait parameters (reference height, H′ and sharpness factor, ꞵ) and changes in the D‐region electron density. In most cases of storms, an increase in the H′ and a decrease in the ꞵ during the storm main and recovery phases were obtained which for the 17–18 March 2013 storm increased by 7.4–7.6 km and decreased from 0.03 to 0.07 km−1, respectively. Wavelet analysis of signal anomalies showed clear wave‐like spectra (0.05–0.18 mHz) of atmospheric gravity waves indicating traveling ionospheric disturbances propagating toward low latitudes due to storm‐associated Joule heating at high latitudes.

Influence of geomagnetic disturbances on scintillations of GLONASS and GPS signals as observed on the Kola Peninsula

We have compared effects of geomagnetic disturbances during magnetic storms of various types (CME and CIR) and during an isolated substorm on scintillations of GLONASS and GPS signals, using a Septentrio PolaRx5 receiver installed in Apatity (Murmansk Region, Russia). We analyze observational data for 2021. The magnetic storms of November 3–4, 2021 and October 11–12, 2021 are examined in detail. The November 3–4, 2021 magnetic storm was one of the most powerful in recent years. The analysis shows that the scintillation phase index reaches its highest values during nighttime and evening substorms (σϕ≈1.5–1.8), accompanied by a negative bay in the magnetic field. During magnetic storms, positive bays in the magnetic field, associated with an increase in the eastward electrojet, lead, however, to quite comparable values of the phase scintillation index.
 An increase in phase scintillations during nighttime and evening disturbances correlates with an increase in the intensity of ULF waves (Pi3/Pc5 pulsations) and with the appearance of aurora arcs. This confirms the important role of ULF waves in forming the auroral arc and in developing ionospheric irregularities. The predominance of the green line in the spectrum of auroras indicates the contribution of disturbances in the ionospheric E layer to the scintillation increase. Pulsating auroras, associated with ionospheric disturbances in the D layer, do not lead to a noticeable increase in phase scintillations. Analysis of ionospheric critical frequencies according to ionosonde data from the Lovozero Hydrometeorological Station indicates the contribution of the sporadic Es layer of the ionosphere to jumps in phase scintillations.
 The difference between phase scintillation values on GLONASS and GPS satellites during individual disturbances can be as great as 1.5 times, which may be due to different orbits of the satellites. At the same time, the level of GLONASS/GPS scintillations at the L2 frequency is higher than at the L1 frequency. We did not find an increase in the amplitude index of scintillations during the events considered.

Влияние геомагнитных возмущений на сцинтилляции сигналов ГЛОНАСС и GPS спутников по данным наблюдений на Кольском полуострове

We have compared effects of geomagnetic disturbances during magnetic storms of various types (CME and CIR) and during an isolated substorm on scintillations of GLONASS and GPS signals, using a Septentrio PolaRx5 receiver installed in Apatity (Murmansk Region, Russia). We analyze observational data for 2021. The magnetic storms of November 3–4, 2021 and October 11–12, 2021 are examined in detail. The November 3–4, 2021 magnetic storm was one of the most powerful in recent years. The analysis shows that the scintillation phase index reaches its highest values during nighttime and evening substorms (σϕ≈1.5–1.8), accompanied by a negative bay in the magnetic field. During magnetic storms, positive bays in the magnetic field, associated with an increase in the eastward electrojet, lead, however, to quite comparable values of the phase scintillation index.
 An increase in phase scintillations during nighttime and evening disturbances correlates with an increase in the intensity of ULF waves (Pi3/Pc5 pulsations) and with the appearance of aurora arcs. This confirms the important role of ULF waves in forming the auroral arc and in developing ionospheric irregularities. The predominance of the green line in the spectrum of auroras indicates the contribution of disturbances in the ionospheric E layer to the scintillation increase. Pulsating auroras, associated with ionospheric disturbances in the D layer, do not lead to a noticeable increase in phase scintillations. Analysis of ionospheric critical frequencies according to ionosonde data from the Lovozero Hydrometeorological Station indicates the contribution of the sporadic Es layer of the ionosphere to jumps in phase scintillations.
 The difference between phase scintillation values on GLONASS and GPS satellites during individual disturbances can be as great as 1.5 times, which may be due to different orbits of the satellites. At the same time, the level of GLONASS/GPS scintillations at the L2 frequency is higher than at the L1 frequency. We did not find an increase in the amplitude index of scintillations during the events considered.

Simultaneous Global Ionospheric Disturbances Associated With Penetration Electric Fields During Intense and Minor Solar and Geomagnetic Disturbances

AbstractA new observational phenomenon, named Simultaneous Global Ionospheric Density Disturbance (SGD), is identified in GNSS total electron content (TEC) data during periods of three typical geospace disturbances: a Coronal Mass Ejection‐driven severe disturbance event, a high‐speed stream event, and a minor disturbance day with a maximum Kp of 4. SGDs occur frequently on dayside and dawn sectors, with a ∼1% TEC increase. Notably, SGDs can occur under minor solar‐geomagnetic disturbances. SGDs are likely caused by penetration electric fields (PEFs) of solar‐geomagnetic origin, as they are associated with Bz southward, increased auroral AL/AU, and solar wind pressure enhancements. These findings offer new insights into the nature of PEFs and their ionospheric impact while confirming some key earlier results obtained through alternative methods. Importantly, the accessibility of extensive GNSS networks, with at least 6,000 globally distributed receivers for ionospheric research, means that rich PEF information can be acquired, offering researchers numerous opportunities to investigate geospace electrodynamics.

Investigation of the Pre- and Co-Seismic Ionospheric Effects from the 6 February 2023 M7.8 Turkey Earthquake by a Doppler Ionosonde

During the catastrophic M7.8 earthquake in Turkey on 6 February 2023, anomalous effects were revealed in the ionosphere associated with various propagation mechanisms of seismogenic disturbance from the lithosphere up to the height of the ionosphere. Seventeen minutes after the main shock, a co-seismic disturbance was detected by a Doppler ionosonde on an inclined, 3010 km long, two-hop radio path “Kuwait—Institute of Ionosphere (Almaty)”. An appearance of acoustic waves at the height of 232 km in the ionosphere was fixed 568 s after arrival of the surface Rayleigh wave to the sub-ionospheric point, and such a delay agrees with the calculated propagation time of a vertically moving acoustic wave. The disturbance lasted 160 s, and its double amplitude was above 2 Hz, which noticeably exceeds the background fluctuation of Doppler frequency. The best coincidence between the waveforms of the Doppler signal and of the surface seismic wave was observed over the duration of the two leading periods, with correlation coefficients of 0.86 and 0.79, correspondingly. Pre-seismic effects in the ionosphere were revealed 8 days before the main shock both in the variations of the Doppler frequency and of the critical frequency f0F2. The probable origination mechanism of the pre-seismic ionospheric disturbances above the region of the earthquake preparation determined by the Dobrovolsky radius may be considered in accordance with the concept of lithospheric–atmospheric–ionospheric coupling.

Large-scale traveling ionospheric disturbances over central and eastern Europe during moderate magnetic storm period on 22–24 September 2020

We present the results of ground based remote sensing observations of large-scale traveling ionospheric disturbances (LSTIDs) occurring during the moderate magnetic storm evolution (22–24 September 2020) over central and eastern Europe. Three ionosondes located in Juliusruh, Pru˚honice and near Kharkiv, and the Kharkiv incoherent scatter radar were employed to study temporal and spatial LSTID signatures in ionospheric F2 peak density and height and electron density variations at the heights of 100–300 km. Two types of LSTIDs are detected, which are originated during enhancement in auroral activity (2 events) and local sunrise terminator passage (3 events) from the ionosonde data. The magnetic storm-related LSTIDs exhibit equatorward propagation with the horizontal phase velocities of 546 m/s and 576 m/s, similar dominant periods of 135–150 min and 165–180 min over all three sites and a longitudinal dependence in fractional (relative) amplitudes of electron density perturbation. The solar terminator induced LSTIDs demonstrate the variety in both relative amplitudes and dominant periods over different locations. They have a westward apparent horizontal phase velocities of 288–345 m/s, which are close to the solar terminator velocity at ionospheric heights. Employment of incoherent scatter data enabled the detection of additional LSTIDs over Ukraine with the periods in a broader range of 41–168 min, an establishment of phase and onset differences for the oscillations in the ionospheric F2 peak electron density and height.

Analysis of Ionospheric Disturbances during X-Class Solar Flares (2021–2022) Using GNSS Data and Wavelet Analysis

The influence of solar activity on the ionosphere, a critical area of investigation due to its relevance to the Sun–Earth relationship, has been extensively examined through various methodologies. The ability of solar events to induce disturbances in both the ionosphere and the geomagnetic field is widely acknowledged. This specific study focused on sporadic incidents resulting from X-class solar flares that occurred between 2021 and 2022. Utilizing a methodology that involved analyzing data at 5Hz intervals using wavelet algorithms, the data from the GNSS stations of the National Autonomous University of Mexico (UNAM) were investigated. The primary emphasis was on deducing the Total Electron Content (TEC) within the ionosphere. Subsequently, this parameter for each satellite during instances of solar flares was analyzed. The approach uncovered disruptions in the ionosphere triggered by solar flares, even in cases where events transpired at the periphery of the solar disk and were of magnitudes smaller than X2.

Driving Source of Change for Ionosphere before Large Earthquake -Vertical Ground Motion-

This paper discusses the relationship between the vertical ground motion and ionospheric disturbances before the Kumamoto earthquake on 16 April 2016, in Kyushu, Japan, using the vertical ground motion measured by slant gauges widely distributed in Kyushu, and the NmF2 observed by ionosondes in Japan and another region. We provide evidence that vertical ground motion excites internal gravity waves (IGWs) that disturb changes in the ionospheric plasma density. From the spectral analysis results of the vertical ground motion data, the summation of various period (frequency) components analyzed from the original data of the slant gauge shows a possible correlation with the change of NmF2 before the earthquake. On the other hand, the influence of the geomagnetic disturbance on vertical ground motion seems to exist. However, we cannot confirm that vertical ground motion is influenced by the geomagnetic disturbance (Kp index) and that the earthquake is triggered by the geomagnetic disturbance. There are two conditions for the vertical ground motion to disturb variations in the ionospheric plasma density: (1) The effective vertical ground motion period should be shorter than 5 h. In addition, (2) vertical ground motion should continue to exist so that wave energy can be continuously injected into the atmosphere. A possible mechanism with which to modify the ionosphere is discussed. The results of this study can provide a basis for the future ionospheric precursors of earthquakes by using the vertical ground motion.

Lower Atmospheric Sources of Observed Thermosphere Medium Scale Traveling Atmospheric Disturbances Over Alaska During the 2012–2013 Winter Months

AbstractThis paper investigates the lower‐to‐upper atmosphere coupling at high latitudes (>60°N) during the northern winter months of 2012–2013 years, which includes a period of major Sudden “Stratospheric” Warming (SSW). We perform statistical analysis of thermosphere wind disturbances with periods of 30–70 min, known as the medium scale traveling atmospheric disturbances (MSTADs) in atomic oxygen green line (557.7 nm) near ∼120 km and red line (630.0 nm) emissions near ∼250 km observed from Scanning Doppler Imagers (SDIs) over Alaska. The SDI MSTADs observations (60°–75°N) are interpreted in conjunction with the previous daytime medium‐scale traveling ionospheric disturbance (MSTID) observations by SuperDARN midlatitudes (35°–65°N) radars in the F‐region ionosphere and western hemisphere, which confirm findings from the SDI instruments. Increases in MSTAD activity from SDIs show correlations with the increasing meridional planetary wave (PW) amplitudes in the stratosphere derived from MERRA2 winds. Furthermore, a detailed study of the lower atmospheric conditions from MERRA2 winds indicates that the lower atmospheric sources of MSTADs are likely due to the stratospheric generated Gravity Waves (GWs) and not orographic GWs. Favorable stratospheric propagation conditions and polar vortex disturbances resulting from the increased PW activity in the stratospheric region both appear to contribute to increased MSTAD activity in the thermosphere. Additionally, the results show that the MSTID activity from SuperDARN HF radars at mid latitudes during the January 2013 SSW is lower than the MSTAD activity in SDI winds at high latitudes.

Signature of thunderstorm induced acoustic and gravity waves at low latitude Indian sector

This study reports thunderstorm-generated acoustic and gravity waves from a tropical location using newly launched Indian navigation system NavIC for the first time. The detection of acoustic wave components in travelling ionospheric disturbance (TID) measurement is very significant. In compared to acoustic wave gravity wave signature is more ubiquitous because gravity wave propagates in thermospheric altitude by dissipative filtering process. The turbulent nature in plasma characteristics due to strong vertical drift and plasma motion in lower latitude region generate strong scintillation effect and plasma bubble. Large temperature gradient at thermospheric altitude also provides a strong attenuation effect in this region for comparatively high frequency acoustic wave. We have found the TID signatures on TEC variation for acoustic wave up to 0.4 TECU for both the days whereas gravity wave induced signatures went up to 0.8 TECU. Measurements using GPS signal validate signatures obtained from the NavIC signal. The study shows the potential of application of NavIC system for middle atmosphere as well as thermospheric study and understanding of coupling process between various atmospheric layers in tropical region which is not well known so far.

Comparison of a Bottom-Up GNSS Radio Occultation Method to Measure D- and E-Region Electron Densities with Ionosondes and FIRI

High-frequency skywave propagation can be heavily impacted by D- and E-region dynamics requiring accurate global measurements to optimize performance. A standard measurement technique is to use ionosondes, but they are unable to measure below 1 MHz and are only available at a limited number of land-locked sites around the globe. In contrast, the Global Navigation Satellite System radio occultation (GNSS-RO) bottom-up method is a new approach specifically designed to generate electron density profiles in the D- and E- region ionosphere. It takes advantage of satellite constellations that currently provide over 20,000 daily measurements and global coverage. In this paper, GNSS-RO profiles were compared against ionosonde profiles at four sites covering a wide latitudinal range, and FIRI modeled profiles corresponding to the same latitude and local solar time. This comparison was completed using daytime profiles when sporadic-E (Es) was not present. The average GNSS-RO profile is found to be a few kilometers higher in altitude than the ionosonde profiles at the minimum frequency, fmin. When the ionosonde profiles are shifted so that the altitudes match at fmin, they are in good agreement up to the E-region peak altitude, hmE. Below fmin, the GNSS-RO profile is in good agreement with the FIRI profile, indicating that the profiles can measure the D- to E- transition region. The frequency of the E-region peak, foE, showed general agreement between the GNSS-RO and ionosonde measurements; however, the hmE agreement was weaker and the GNSS-RO profiles tend to have an hmE in a narrow altitude range for all profiles. Virtual heights were simulated for the GNSS-RO profiles using a numerical ray tracer for direct comparison with ionosonde observations, which showed agreement for many of the virtual heights near fmin, but also indicated a positive bias in the GNSS-RO virtual heights that may be due to low foE or elevated hmE estimates. For a quiet ionosphere, the shifted GNSS-RO electron density profiles were a good match for both measured ionosonde profiles and modeled FIRI profiles and the method is capable of providing global coverage of the D- and E-regions. Future work will require more data for seasonal and morning–afternoon comparisons as well as comparisons for the disturbed ionosphere when the sporadic-E layer is present.

Rapid Detection of Co‐Seismic Ionospheric Disturbances Associated With the 2015 Illapel, the 2014 Iquique and the 2011 Sanriku‐Oki Earthquakes

AbstractCo‐seismic Ionospheric disturbances (CID, or “ionoquakes”) are disturbances in the electron density or total electron content (TEC) of the ionosphere, produced by the ground motion due to earthquakes. Usually, ionoquakes are detected in the near‐epicentral region within 8–10 min after an earthquake onset time. In this work, we present a new methodology that allows to estimate the CID arrival time based on determining the CID peak time in TEC measurements with respect to the peak time of seismic waves registered by the nearest seismic station. Our methodology also allows to understand the altitude of GNSS detection that otherwise remains ambiguous. We apply the newly developed techniques to detect CID signatures associated with three large earthquakes: the 2015 Illapel, the 2014 Iquique, and the 2011 Sanriku‐Oki. We show that for these events, the CID arrive 250–430 s after the time of the seismic wave peak, or 350–700 s after the earthquake onset time. Our analysis show that the first CID are detected at the altitudes of 150–180 km (the Sanriku earthquake) and of 200–300 km (the Illapel and the Iquique earthquakes). The disturbances represent high‐frequency acoustic oscillations that propagate with a horizontal speed faster than 0.75 km/s.

The 6 February 2023 Türkiye Earthquake Sequence as Detected in the Ionosphere

AbstractOn 6 February 2023, a series of large earthquakes struck Turkey and Northern Syria. The main earthquake of Mw 7.8 occurred at 01:17:34 UTC and was followed by the three notable (Mw > 5.5) aftershocks within the next 18 min. Then, ∼9 hr later, the biggest aftershock with magnitude Mw 7.5 and a Mw 6.0 earthquake occurred to the north‐east from the first main earthquake. In this work, we use data of ground‐based Global Navigation Satellite Systems (GNSS) receivers in Turkey, Israel and Cyprus to analyze the ionospheric response to this series of earthquakes. We separate these events in two groups: the first sequence of earthquakes (at 01–02 UTC) and the second sequence (at 10–11 UTC). For the first sequence, we observe a clear N‐shaped total electron content (TEC) response after the Mw 7.8 mainshock earthquake and Mw 6.7 aftershock, and a smaller TEC disturbance that is, most likely, caused by the Mw 5.6 earthquake. The latter is now the smallest earthquake detected by using ionospheric GNSS data. The co‐seismic ionospheric disturbances (CSID) propagated from the epicentral area in the south‐west direction with velocities of about 750–830 m/s. For the second sequence, we observed the response to the Mw 7.5 aftershock earthquake and the Mw 6.0 aftershock. The CSID propagated both to the south‐west and the north‐west to the epicentral area, with velocities of about 950–1,100 m/s.