Ionospheric Hole Research Articles

Enhancement of ionospheric heating effect by chemical release

The ionosphere can be artificially modified by employing ground-based high-power high-frequency electromagnetic waves to irradiate the ionosphere. This modification is achieved through the nonlinear interaction between the electromagnetic waves and the ionospheric plasma, leading to changes in the physical properties and structure of the ionosphere. The degree of artificial modification of the ionosphere is closely related to the heating energy density of high-frequency pump waves. Due to the high density of neutral constituents in the lower ionosphere and the high frequency of electron-neutral collisions, the energy of heating pump waves will be absorbed and attenuated during the penetration of the low ionosphere, seriously affecting the heating effect. This paper proposes a method to reduce the absorption of ionospheric heating pump waves by releasing electron attachment chemicals into low ionosphere to form a large-scale electron density hole. A model for mitigating pump waves absorption based on SF6 release is established, and the absorption at different frequencies is quantitatively calculated. The propagation characteristics of high-frequency signals in ionospheric holes are studied using a three-dimensional ray tracing method, and the results demonstrate that the chemical release method not only reduces the absorption attenuation of heating pump waves but also forms spherical electron density holes, which exhibit a focusing effect on the heating beam and enhance the heating effect. The results are of great significance for understanding the nonlinear interaction between electromagnetic wave and ionospheric plasma and improving the ionospheric heating efficiency.

Giant ionospheric density hole near the 2022 Hunga-Tonga volcanic eruption: multi-point satellite observations

A giant ionospheric hole was simultaneously detected in the in situ measurements of FORMOSAT-7/COSMIC-2 (F7/C2), Ionospheric Connection Explorer (ICON), Swarm missions, and ground-based total electron content (TEC) by global navigation satellite system receivers, and F7/C2 Global Ionosphere Specification (GIS) data near Tonga, following the explosive volcano eruption on 15 January 2022. The TEC maps displayed the huge depletions that developed near Tonga after the eruption and gradually evolved. The ICON IVM, F7/C2 IVM and Swarm-LP detected large depletions not only near Tonga, but also in the EIA trough region. The GIS observations clearly show the ionospheric hole that extends spatially near Tonga, especially strongly south/southward. The simultaneous observations showed that the ionosphere hole near Tonga combined with the EIA trough and finally evolved into a giant ionosphere hole around 07 UT. The ionospheric hole, which occurred at 05 UT near Tonga, extended over a wide area of 160°-200°E and 25°S-20°N and lasted for about 11 h. The F7/C2 and ICON satellites overpasses showed large ion density depletions by the hole at orbit altitudes, accompanied by enhancements in ion temperature and field-aligned and perpendicular ion drift. Such a long-lasting giant ionospheric hole by a seismic event has not been reported earlier, creating a unique ionospheric environment near Tonga after the eruption. The strong successive impulses by multiple volcano eruptions, together with O/N2 decrease in the summer hemisphere, interhemispheric wind, and water vapor injection into high altitudes apparently yielded such a giant ionospheric hole, 4–6 times larger than that observed during the Tohoku earthquake.Graphical

Physical effects from the powerful Tonga volcanic eruption of January 15, 2022, in the earth–atmosphere–ionosphere–magnetosphere system

The powerful Tonga volcanic explosion and eruption has been reliably determined to cause numerous processes on a global scale; nevertheless, a comprehensive model of these processes is absent in the literature, which remains an urgent scientific objective. The purpose of this paper is to thoroughly analyze and model the main physical processes that accompanied the volcanic explosion within the Earth (lithosphere, tectonosphere, ocean) – atmosphere – ionosphere – magnetosphere (EAIM) system on January 15, 2022. The study attempts, for the first time, to comprehensively model or estimate the magnitude of the main effects arising in the solid Earth, the troposphere, the ionosphere, and in the magnetosphere. The effects include a rich assortment of waves: Lamb, sound, seismic, tsunami, infrasonic, and atmospheric gravity waves, which propagated on a global scale, with the blast wave launching secondary tsunamis and seismic waves. The powerful waves nonlinearly distorted their profiles and suffered nonlinear attenuation, while the electrical processes in the troposphere caused perturbations in the global electric circuit enhancing the strength of the ionospheric electric fields by one to two orders of magnitude that led to the emergence of secondary processes in the magnetosphere and radiation belts. The volcanic explosion excited all resonators in the EAIM system, perturbing their parameters. Resonances occurred in the Earth's solid shell (Rayleigh wave), in the Earth–ionosphere cavity (Schumann resonances), in the atmosphere (acoustic resonance), in the ionosphere (Alfvén resonances), and in the magnetosphere (magnetospheric resonance). The magnetic effect has been estimated of the submarine volcanic explosion and eruption (∼100–1000 nT), the tsunami (∼0.1 nT), of the volcanic plume (∼1–10 nT), and in the ionosphere due to the ionospheric hole (ΔB ∼ 0.1–10 nT) and an external current in the atmospheric wave field (ΔB ∼ 0.1–1 nT). The magnetospheric effects were caused by electromagnetic emissions in the ∼10–100 kHz band generated by lightning in the volcanic plume, which triggered the precipitation of energetic radiation belt particles into the ionosphere. This is the first time that feedback and main coupling processes, positive and negative, have been observed to emerge among the EAIM system components.

Understanding Nighttime Ionospheric Depletions Associated With Sudden Stratospheric Warmings in the American Sector

AbstractThis study focuses on understanding what drives the previously observed deep nighttime ionospheric hole in the American sector during the January 2013 sudden stratospheric warming (SSW). Performing a set of numerical experiments with the thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) constrained by a high‐altitude version of the Navy Global Environmental Model, we demonstrate that this nighttime ionospheric hole was the result of increased poleward and down magnetic field line plasma motion at low and midlatitudes in response to altered F‐region neutral meridional winds. Thermospheric meridional wind modifications that produced this nighttime depletion resulted from the well‐known enhancements in semidiurnal tidal amplitudes associated with stratospheric warming (SSWs) in the upper mesosphere and thermosphere. Investigations into other deep nighttime ionospheric depletions and their cause were also considered. Measurements of total electron content from Global Navigation Satellite System receivers and additional constrained TIME‐GCM simulations showed that nighttime ionospheric depletions were also observed on several nights during the January‐February 2010 SSW, which resulted from the same forcing mechanisms as those observed in January 2013. Lastly, the recent January 2021 SSW was examined using Modern‐Era Retrospective Analysis for Research and Applications, Version 2, COSMIC‐2 Global Ionospheric Specification electron density, and ICON Michelson Interferometer for Global High‐Resolution Thermospheric Imaging horizontal wind data and revealed a deep nighttime ionospheric depletion in the American sector was likely driven by modified meridional winds in the thermosphere. The results shown herein highlight the importance of thermospheric winds in driving nighttime ionospheric variability over a wide latitude range.

PHYSICAL EFFECTS OF THE POWERFUL TONGA VOLCANO EXPLOSION IN THE EARTH – ATMOSPHERE – IONOSPHERE – MAGNETOSPHERE SYSTEM ON JANUARY 15, 2022

PHYSICAL EFFECTS OF THE POWERFUL TONGA VOLCANO EXPLOSION IN THE EARTH – ATMOSPHERE – IONOSPHERE – MAGNETOSPHERE SYSTEM ON JANUARY 15, 2022

Lithosphere Ionosphere Coupling Associated with Seismic Swarm in the Balkan Peninsula from ROB-TEC and GPS

With the rapid development of global navigation satellite systems (GNSS) and their increasingly wide range of applications in atmospheric science, total electron content (TEC) data are widely used in the theoretical study of layer coupling related to seismicity. This study detected and analyzed pre-earthquake ionospheric anomalies (PEIA) by using TEC data from the Royal Observatory of Belgium (ROB), and analyzed coseismic ionospheric disturbance (CID) with vertical TEC (VTEC) from the GPS stations in earthquake preparation areas. The results show that PEIA appear to increase continuously from 08:00–12:00 UT in the 3 days before a seismic swarm of Mw > 5.0. The ionosphere over the seismogenic zones exhibited large-scale anomalies when multiple seismogenic zones of the Balkan Peninsula spatially and temporally overlapped. Moreover, the TEC around the earthquake centers showed a positive anomaly lasting for 7 h. In a single seismogenic zone in Greece, the TEC around the earthquake center reached over +3.42 TECu. In addition, the CID observed from GPS stations shows that with the increase in the number of earthquakes, the ionosphere over the seismogenic area is more obviously disturbed, and after three strong earthquakes, TEC suddenly decreased over the seismogenic area and formed a phenomenon similar to an ionospheric hole. We conclude that a lithosphere–atmosphere–ionosphere coupling mechanism existed before the seismic swarm appeared in the Balkan Peninsula. Earthquake-induced VTEC anomalies occurred more frequently within a 3–10 day window before the earthquake. This phenomenon is particularly evident when multiple seismogenic zones overlap spatiotemporally.

Significant Ionospheric Hole and Equatorial Plasma Bubbles After the 2022 Tonga Volcano Eruption

AbstractThis paper investigates the local and global ionospheric responses to the 2022 Tonga volcano eruption, using ground‐based Global Navigation Satellite System total electron content (TEC), Swarm in situ plasma density measurements, the Ionospheric Connection Explorer (ICON) Ion Velocity Meter (IVM) data, and ionosonde measurements. The main results are as follows: (a) A significant local ionospheric hole of more than 10 TECU depletion was observed near the epicenter ∼45 min after the eruption, comprising of several cascading TEC decreases and quasi‐periodic oscillations. Such a deep local plasma hole was also observed by space‐borne in situ measurements, with an estimated horizontal radius of 10–15° and persisted for more than 10 hr in ICON‐IVM ion density profiles until local sunrise. (b) Pronounced post‐volcanic evening equatorial plasma bubbles (EPBs) were continuously observed across the wide Asia‐Oceania area after the arrival of volcano‐induced waves; these caused a Ne decrease of 2–3 orders of magnitude at Swarm/ICON altitude between 450 and 575 km, covered wide longitudinal ranges of more than 140°, and lasted around 12 hr. (c) Various acoustic‐gravity wave modes due to volcano eruption were observed by accurate Beidou geostationary orbit (GEO) TEC, and the huge ionospheric hole was mainly caused by intense shock‐acoustic impulses. TEC rate of change index revealed globally propagating ionospheric disturbances at a prevailing Lamb‐wave mode of ∼315 m/s; the large‐scale EPBs could be seeded by acoustic‐gravity resonance and coupling to less‐damped Lamb waves, under a favorable condition of volcano‐induced enhancement of dusktime plasma upward E×B drift and postsunset rise of the equatorial ionospheric F‐layer.

Numerical Simulation of Ionospheric Disturbances Due to Rocket Plume and Its Influence on HF Radio Waves Propagation

In this paper, the ionospheric disturbances of CO2, which is released by rocket exhaust plumes, was simulated. The effect of this disturbance on the propagation of high-frequency (HF) radio waves at different incident frequencies was also simulated by using three-dimensional digital ray tracing technique. The results show that CO2 can effectively dissipate the background electrons and form ionospheric holes after being released in the ionosphere. At the peak height of ionospheric electron density (about 300 km), the electrons are dissipated fastest and the radius of ionospheric hole is also largest. This is due to the fact that the diffusion coefficient of CO2 usually increases with height while the electron density just increases before reaching its peak height and then decreases with height, and the chemical reaction rate between ions and CO2 also becomes largest at the peak height of electron density (about 300 km). Around 100 s after the release of CO2, when the radio waves at a frequency of 8 MHz pass through the ionosphere with an elevation range of 85~95°, the “secondary focusing effect” can occur, and we believe that this is due to the reflection of HF shortwaves on the walls of the ionospheric holes. With time going on, this phenomenon disappears at 300 s and only one focus is left at this time. For the HF shortwaves at same incident frequency, the focusing effect of waves displays a weakening trend with time increasing, and the height of focus center also ascends gradually. At the same time after CO2 releasing, with the increasing of radio waves frequency, the focusing effect also becomes weaker and the focus center displays an ascending trend.

LARGE-SCALE REDUCTIONS IN THE ELECTRON DENSITY OF IONOSPHERIC F-REGION, OBSERVABLE ALONG ROCKET TRAJECTORIES AT LAUNCH

Purpose. The object of the study are electron density depletions (‘holes’) occurring in the ionospheric F-region under the action of rocket exhaust products. The purpose is to present and discuss the results of observations concerning the ionospheric holes that were detected in the course of a number of launches of medium-lift Kosmos vehicles from the Kapustin Yar spaceport. Nei- ther that cosmodrome, nor the rocket type had been subjects of similar analysis before. Design/methodology/approach. The observations at the Kapustin Yar cosmodrome were performed with a portable vertical Doppler sounder. The beats between a reference signal and the one reflected from the ionosphere were subjected to spectral analysis, which allowed identifying the principal mode of the Doppler frequency shift and establishing time dependences of that frequency shift. An ionosonde located nearby was used for monitoring the underlying state of the ionosphere. Findings. The measurements performed with the vertical Doppler sounder near the launch site of the medium-lift Kosmos rocket have allowed obtaining first estimates for the principal parameters of the ionospheric holes arising in the F-region along the vehicle trajectory, as well as for the accompanying quasi-periodic variations in the electron density. The spatial scale sizes of the holes have been found to be in excess of 300 km, while the electron density reductions may attain » 50 %. These results are in agreement with the data obtained by international researchers for effects from heavy- and super heavy-lift launch vehicles. Also, note that the types of propellant differed significantly. The propagation velocity of the hole’s front edge was estimated to be » 140 m/s. The hole formation was accompanied by quasi-periodic variations in the Doppler frequency shift as a result of radar signal scattering from the electron density fluctuations produced by propagating atmospheric gravity- and infrasonic waves. The atmospheric gravity waves showed periods in the range from 7 to 20 minutes, and the infrasonic waves had a period close to 2 min. The amplitudes of quasi-periodic electron density variations were estimated for the two modes to be » 0.3 ¸1.5 % and » 0.02 ¸ 0.03 %, respectively. Conclusions. Medium-lift launch vehicles (mass of a few hundred tons) are capable of forming ionospheric ‘holes’ of several hundred kilometers in size and of reducing the electron density in the F-region by a factor greater than 2.

Robust uncertainty quantification of the volume of tsunami ionospheric holes for the 2011 Tohoku-Oki earthquake: towards low-cost satellite-based tsunami warning systems

Abstract. We develop a new method to analyze the total electron content (TEC) depression in the ionosphere after a tsunami occurrence. We employ Gaussian process regression to accurately estimate the TEC disturbance every 30 s using satellite observations from the global navigation satellite system (GNSS) network, even over regions without measurements. We face multiple challenges. First, the impact of the acoustic wave generated by a tsunami onto TEC levels is nonlinear and anisotropic. Second, observation points are moving. Third, the measured data are not uniformly distributed in the targeting range. Nevertheless, our method always computes the electron density depression volumes, along with estimated uncertainties, when applied to the 2011 Tohoku-Oki earthquake, even with random selections of only 5 % of the 1000 GPS Earth Observation Network System receivers considered here over Japan. Also, the statistically estimated TEC depression area mostly overlaps the range of the initial tsunami, which indicates that our method can potentially be used to estimate the initial tsunami. The method can warn of a tsunami event within 15 min of the earthquake, at high levels of confidence, even with a sparse receiver network. Hence, it is potentially applicable worldwide using the existing GNSS network.

Magnetic Topology at Venus: New Insights Into the Venus Plasma Environment

AbstractThis study provides the first characterization of magnetic topology (i.e., the magnetic connectivity to the collisional ionosphere) at Venus, which might give new insights into the Venusian space environment on topics such as the penetration of the interplanetary magnetic field (IMF) into the ionosphere, planetary ion outflow and inflow, and auroral emission. Magnetic topology is inferred from the electron and magnetic field measurements from Venus Express. We demonstrate through a few case studies that various types of magnetic topologies exist at Venus, including typical draped IMF, open magnetic fields connected to the nightside atmosphere or the dayside ionosphere, and unexpected cross‐terminator closed field lines. We also provide a detailed characterization of an ionospheric hole event, where we find an open topology and a field‐aligned potential of V with respect to the collisional ionosphere, which has important implications for its formation mechanism.

Explore the Echo Characteristics of HF Radar in Artificial Disturbance Ionosphere Using Ray‐Tracing Technology

AbstractArtificial ionospheric hole created by the release of neutral gases (such as sulfur hexafluoride) has a significant impact on the propagation of radio waves. Based on the ray‐tracing method, the propagation patterns of HF radio waves in the ionospheric hole and the characteristics of its echoes are discussed in this paper. The results show that the HF waves will be deflected and bended while passing through the ionospheric hole, thus changing its original path. The sounding frequency, elevation angle, position of transmitter and receiver, and the dynamic variation of the hole all affect the reception of echoes. Generally, when the frequency is low, the echoes received on the ground mainly come from rays with low‐elevation angles, and the multi‐hop rays are more likely to occur. While with a high frequency, the received echoes are mainly contributed by high‐elevation rays. It is not conducive to the reception of the echoes if the transmitter and receiver is too far away from the hole. Single‐peak, double‐peak and multi‐peak echo signals can be found in the group path‐amplitude diagram, and the maximum group path difference can reflect the size of the ionospheric hole to some extent. Due to the dynamic evolution of the hole, the propagation of HF waves and received echoes also changes over time. The group path‐time diagrams show that the come‐back echoes mainly appear in the period of 20–100 s after release. The results of this paper have a guiding significance for the diagnosis and application of active experiments.

Impact of the Ionosphere Disturbed by Rocket Plume on OTHR Radio Wave Propagation

AbstractThe main chemicals of rocket exhaust plume are released into the ionosphere, which cause three‐dimensional (3‐D) disturbances. By simulating the disturbance, we investigate the influence of ionospheric disturbance by the chemical release on the propagation of over‐the‐horizon radar (OTHR) waves. Based on the absorption simulation model, the absorption loss of OTHR waves caused by rocket plume was simulated. Using 3‐D digital ray tracing, we simulated the propagation path of radio waves in the “ionospheric hole” region. The simulation results show that the absorption loss of short waves decreases with an increase in the frequency and elevation angle of the ray. The absorption loss in the year of high solar activity is significantly higher than that in the year of low solar activity. The absorption value is largest at noon and smallest at night. In terms of seasonal variation, the absorption of radio waves is strongest in summer and weakest in winter. Additionally, the ionospheric hole area increases with the release time. The 6 MHz high‐frequency waves cannot reach the disturbance height and are completely reflected to the ground. Most of the 8 MHz radio waves are reflected to the ground, and some of them pass through the ionosphere. The radio waves at 10, 15, and 20 MHz can pass through the hole area of the ionosphere. Moreover, the ionospheric disturbance generated by the plume has a focusing effect on the propagation of OTHR shortwaves. With the increase in radio frequency, the focusing height gradually increases, and the focusing effect gradually weakens.

The TEC Enhancement Before Seismic Events Is an Artifact

AbstractSince 2011 there has been an ongoing debate about the possibility of short‐term earthquake prediction using total electron content (TEC) ionospheric monitoring by the Global Navigation Satellite System (GNSS). Heki (2011), https://doi.org/10.1029/2011gl047908 initiated this debate when he published results for the 2011 Tohoku event reporting a TEC enhancement 40 min before the earthquake; several later papers by Heki and coworkers have made similar claims for other earthquakes. If correct, Heki's methods might contribute to short‐term earthquake prediction. However, Heki's claims have been strongly criticized as being due to a decrease in the background TEC after earthquakes–the so called ionospheric hole–rather than an enhancement before. Depending on the choice of reference curve to be subtracted from the raw data to infer the “anomaly,” the data analysis can produce either a hole or an enhancement. We show that the choice of reference curve ‐calculated by Heki with a polynomial fit‐is strongly affected by the degree of the polynomial, as well as by the selection of the time window. We also show using synthetic examples that even if there is actually no signal before the event, Heki's methods can lead to spurious precursory signals (i.e., signals with non‐zero amplitude before the event) after the reference curve is subtracted. It thus appears likely that the reported TEC enhancements are artifacts.

Numerical Simulation of Ionospheric Depletions Resulting From Rocket Launches Using a General Circulation Model

AbstractRocket exhaust plumes have been observed to cause large‐scale depletions of ionospheric plasmas (“ionospheric holes”). In the F region, charge exchange reactions occur between O+ ions and exhaust species such as H2O, H2, and CO2 to form ions, which then undergo rapid dissociative recombination. The Global Ionosphere‐Thermosphere Model (GITM) was extended to include these chemical reactions and appropriate source terms to represent rocket exhaust plumes. The resulting model allowed for the detailed simulation of advection, diffusion, and chemical interactions of rocket exhaust gasses in the upper atmosphere. This model was applied to ionospheric depletions resulting from the launches of Jason‐3 and FORMOSAT‐5 on SpaceX Falcon 9 rockets from Vandenberg Air Force Base. Outputs from the model were compared with GNSS, ionosonde, and satellite Langmuir probe measurements. Simulation indicated that the FORMOSAT‐5 launch resulted in a far larger and longer‐lived ionospheric depletion than the Jason‐3 launch, consistent with observations. These differences resulted primarily from the deposition of exhaust gasses at higher altitudes in the former case, which resulted in longer residence times in the upper F region where ionospheric plasma was replenished more slowly. Simulation of the FORMOSAT‐5 launch reproduced the approximate size, shape, and motion of the observed ionospheric depletion, which reflected the advection and diffusion of the rocket exhaust gasses through the thermosphere.

Ionospheric Regions Producing Anomalous GNSS Radio Occultation Results

Anomalous GPS radio occultation (RO) events are characterised as those with L1 bending angle greater than their corresponding L2 bending angle. An investigation by EUMETSAT and the United Kingdom Meteorological Office revealed there are regions in the earth’s atmosphere where at times up to 60% of Global Navigation Satellite System Receiver for Atmospheric Sounding RO events, at the Tangent Point height of 50 km, exhibited anomalous bending angle results. The exact source of these anomalous RO events has been unclear to the RO data user community, i.e., data processing artifact or atmospheric phenomenon. In this paper, the regions of increased occurrence of anomalous RO have been identified to be the mid-latitude ionospheric trough, ionospheric polar hole, and poleward edges of the equatorial anomaly. They are more frequent at nighttime and in the southern hemisphere winter months. This is when the plasma density in these regions is depleted. However, within these regions, there are ionospheric features of increased electron density gradients such as at the walls of the mid-latitude ionospheric trough. 3-D numerical ray tracing simulations of GPS RO are presented, showing that these increased electron density features in a weakly ionized ionosphere can produce the anomalous bending angle results.

Measurement of plasma channels in the Venus wake

Plasma channels have been suggested to account for the observation of ionospheric holes in the Venus nightside ionosphere. They are produced by the erosion of the solar wind on the magnetic polar regions of the Venus ionosphere, and are related to a sharp plasma transition that extends along the flanks of the wake and that is located downstream from the bow shock. The sharp plasma (intermediate) transition is a feature that has been detected with instruments onboard all the main spacecraft that have probed the Venus wake. From the early flyby transit of the Mariner 5 spacecraft to the later orbit crossings of the Venera 10, the Pioneer Venus and more recently the Venus Express there has been accumulated evidence of the presence of that transition by the flanks of the Venus wake. We report here measurements made with the ASPERA-4 instrument of the Venus Express that were conducted in orbit crossings by the midnight plane over a 4 year period (between 2006 and 2009), and that show different positions of the intermediate transition in the Venus wake at locations closer to the sun-Venus axis near solar minimum conditions by 2009. Measurements conducted in this latter time period also indicate that the intermediate transition by the midnight plane derives from the plasma channels and that is replaced by a broad velocity layer in orbits that probed farther away from that plane. It is argued that changes in the position of the intermediate transition with respect to the plasma channels are related to processes produced by the transport of solar wind momentum to the Venus polar ionosphere. The energy spectra of planetary ions measured in VEX orbits that probed by the midnight plane show momentum transport from the solar wind protons. This result is contrary to the conclusions reported by Collinson et al. (2014) in the sense that there is ¨no difference in the peak energy of the ionospheric outflow¨ when measured inside and outside an ionospheric hole.

Deep Ionospheric Hole Created by Sudden Stratospheric Warming in the Nighttime Ionosphere

AbstractMultiple observational studies have demonstrated large ionospheric variations during the daytime associated with sudden stratospheric warming (SSW) events, but only limited evidence of ionospheric disturbances during the nighttime has been reported up to now. We focus on the American longitudinal sector with its extensive observational network of Global Navigation Satellite System receivers, four Digisondes located at low and middle latitudes, and the Arecibo and Millstone Hill incoherent scatter radars. The study focuses on a major SSW event of January 2013 to investigate large‐scale disturbances in the nighttime ionosphere. We report a deep decrease in total electron content that reaches a factor of 2–5 as compared to the background level and is observed between local midnight and local sunrise (6–12 UT). This decrease is observed for several consecutive days in the range of latitudes from ~55°S to ~45°N. It is accompanied by a strong downward plasma motion and a significant decrease in ion temperature, as observed by both Arecibo and Millstone Hill radars. These results demonstrate that SSW events cause changes in the nighttime ionosphere that are even larger than in the daytime ionosphere. We discuss variations in electric field and F‐region dynamics as possible drivers of this behavior and suggest that thermospheric winds play a much larger role than previously thought.

SAMI2 model results for the quiet time low latitude ionosphere over India

Efficacy of SAMI2 model for the Indian low latitude region around 75°E longitudes has been tested for different levels of solar flux. With a slight modification of the plasma drift velocity the SAMI2 model has been successful in reproducing quiet time ionospheric low latitude features like Equatorial Ionization Anomaly. We have also showed the formation of electron hole in the topside equatorial ionosphere in the Indian sector. Simulation results show the formation of electron hole in the altitude range 800–2500 km over the magnetic equator. Indian zone results reveal marked differences with regard to the time of occurrence, seasonal appearances and strength of the electron hole vis-a-vis those reported for the American equatorial region.

The 4D‐var Estimation of North Korean Rocket Exhaust Emissions Into the Ionosphere

AbstractWe have developed a four‐dimensional variation data assimilation technique (4D‐var) and utilized it to reconstruct three‐dimensional images of the ionospheric hole created during Kwangmyongsong‐4 rocket launch. Kwangmyongsong‐4 was launched southward from North Korea Sohae space center (124.7°E, 39.6°N) at 00:30 UT on 7 February 2016. The data assimilated were Global Positioning System total electron content from the South Korean Global Positioning System‐receiver network. Due to lack of publicized information about Kwangmyongsong‐4, the rocket was assumed to inherit its technology from previous launches (Taepodong‐2). The created ionospheric hole was assumed to be made by neutral molecules, water (H2O) and hydrogen (H2), deposited in exhaust plumes. The dispersion model was developed based on advection and diffusion equation, and a simple asymmetric diffusion model assumed. From the analysis, using the adjoint technique, we estimated an ionospheric hole with the largest depletion existing around 6–7 min after launch and gradually recovering within ~30 min. These results are in agreement with temporal total electron content analyses of the same event from previous studies. Furthermore, Kwangmyongsong‐4 second stage exhaust emissions were estimated as 1.9 × 1026 s−1 of which 40% was H2 and the rest H2O.