Ionospheric Hole Research Articles

Daytime F-region irregularity triggered by rocket-induced ionospheric hole over low latitude

Unexpected daytime F-region irregularities following the appearance of an ionospheric hole have been observed over low latitude. The irregularities developed initially above the F-region peak height (~ 360 km) with a thickness of about 30 km and an east-west extension of more than 200 km around 1057 LT and then expanded upward to 500 km altitude behaving like the equatorial spread-F (ESF) irregularities of the nighttime ionosphere. These daytime F-region irregularities cannot be explained on basis of an earlier suggestion that the F-region irregularities observed during daytime are the continuation of the irregularities initially generated on the previous night. Based on the coincidence, both in space and time, with the appearance of an ionospheric hole, which was generated after the passage of a rocket, we conclude that the daytime F-region irregularities must have been artificially generated locally through a manifestation of plasma instability triggered by the rocket exhaust-induced ionospheric hole over low latitude.

Early time effects produced by neutral gas ionospheric chemical release

The artificial release of electron adsorbing material can cause electron density to be depleted in the ionosphere, forming the ionospheric holes rapidly. At the same time, the shell structure of the electron density enhancement around the hole is produced, owing to the extrusion of background plasma caused by rapid expansion of the release. The coexistence of ionospheric hole and enhancement structure is the significant characteristics of the early time effects. In this paper, the early time effects of neutral chemicals released into ionosphere are studied, and a physical model of spatiotemporal evolution about early time electron density is set up. At t=1 s, the maximum electron density in the enhanced region is 2.46106 cm-3, approximately 2.8 times as great as background electron density, then the electron density at the boundary gradually decreases. At t=30 s, the maximum electron density is 1.58106 cm-3, which is about 1.7 times the background electron density. At t=120 s the maximum electron density in the enhanced region is 1.12106 cm-3, which is 1.2 times the background electron density. Within 120 s after release, the size of the ionospheric cavity increases gradually; at t=5 s the distribution range of the released chemical material is of a sphere of about 10 km in diameter; at t=120 s the distribution diameter of the released chemical material is more than 70 km, and at the same time, the depletion depth of the ionospheric hole decreases slowly. At t=1 s, the depletion depth of the ionospheric hole is about 100%, and at t=120 s the depletion depth of the ionospheric cavity decreases to 95%. The effects of different-frequency radio waves propagating through ionospheric disturbance at t=10 s and t=120 s are simulated by the ray tracing. At t=10 s, the effect of electron density enhancement is remarkable, and the thickness of the enhancement is about 10 km, and the electronic density enhancement area can reflect the radio wave signal at a frequency as high as 14 MHz. At t=120 s, the phenomenon of electron density enhancement becomes weak, the thickness of the enhanced area continues to increase, and the radio wave signal that the electronic density enhancement area could reflect decreases to 11 MHz. The radio waves at a frequency range between 9 MHz and 12 MHz each have a complex diffraction, focusing and dispersing effect in the disturbed area. Furthermore, according to the working principle of ionospheric vertical measurement instrument and ray tracing theory, the vertical ionization detection figures are obtained through inversion. The results are consistent with previous experimental results of rocket exhaust, which testifies the correctness of proposed model.

Coseismic Traveling Ionospheric Disturbances during the Mw 7.8 Gorkha, Nepal, Earthquake on 25 April 2015 From Ground and Spaceborne Observations

AbstractCoseismic traveling ionospheric disturbances (CTIDs) and their propagation characteristics during Mw 7.8 Gorkha earthquake in Nepal on 25 April 2015 have been investigated using a suite of ground‐based GPS receivers and broadband seismometers along with the spaceborne radio occultation observations over the Indian subcontinent region. Depletion in vertical total electron content, a so called ionospheric hole, is observed near the epicenter ~9–11 min after the onset of earthquake. A positive pulse preceding the depletion, similar to N‐shaped perturbation, propagating with an apparent velocity of ~2.4 km/s is observed on the south. Further, the CTIDs in the southward direction are found to split in to fast (~2.4–1.7 km/s) and slow (~680–520 m/s) propagating modes at epicentral distances greater than ~800 km. However, the velocities of fast mode CTIDs are significantly smaller than the surface Rayleigh wave velocity (~3.7 km/s), indicating that they are not the true imprint of Rayleigh wave, instead, can probably be attributed to the superimposed wave front formed by the mixture of acoustic waves excited by main shock and propagating Rayleigh wave. The southward CTIDs are found to propagate at F2 region altitudes of ~300–440 km captured by Constellation Observing System for Meteorology, Ionosphere and Climate radio occultation observations. The CTIDs with periods of ~4–6 min are observed in all directions with significantly larger amplitudes and faster propagation velocities in south and east directions. The observed azimuthal asymmetry in the amplitudes and velocities of CTIDs are discussed in terms of the alignment with geomagnetic field and nature of surface crustal deformation during the earthquake.

A possible space-based tsunami early warning system using observations of the tsunami ionospheric hole.

Ionospheric plasma disturbances after a large tsunami can be detected by measurement of the total electron content (TEC) between a Global Positioning System (GPS) satellite and its ground-based receivers. TEC depression lasting for a few minutes to tens of minutes termed as tsunami ionospheric hole (TIH) is formed above the tsunami source area. Here we describe the quantitative relationship between initial tsunami height and the TEC depression rate caused by a TIH from seven tsunamigenic earthquakes in Japan and Chile. We found that the percentage of TEC depression and initial tsunami height are correlated and the largest TEC depressions appear 10 to 20 minutes after the main shocks. Our findings imply that Ionospheric TEC measurement using the existing ground receiver networks could be used in an early warning system for near-field tsunamis that take more than 20 minutes to arrive in coastal areas.

Does an ionospheric hole appear after an inland earthquake?

AbstractIonospheric disturbances occurred as a result of the tsunami associated with the 2011 M9.0 off the Pacific Coast of the Tohoku earthquake (EQ). The ionospheric disturbances propagated radially from the tsunami source area, termed the traveling ionospheric disturbance. In addition to the traveling ionospheric disturbance, an ionospheric plasma depression lasting for approximately 1 h occurred above the tsunami source area, called a tsunami ionospheric hole. In this study, we compare the ionospheric disturbances caused by large inland and submarine EQs to investigate whether an ionospheric plasma depression only occurs in association with a tsunami. Note that we term an EQ with a tsunami a submarine EQ. To investigate the presence of a plasma depression, i.e., an ionospheric hole, associated with an inland EQ, data on total electron content between the global positioning system satellite and its receivers were used. Comparison of two inland and two submarine EQ events with similar magnitudes around 7 showed that ionospheric holes were observed only for the submarine EQs. This discrepancy might be attributed to the different excitation amplitudes of the atmospheric acoustic waves between the unidirectional fault displacement and the tsunami uplift/depression, corresponding to quarter and one‐period variations. From this hypothesis, we predicted that an ionospheric hole could be observed after a significantly large inland EQ with a sufficiently large vertical ground displacement. In fact, we recognized the ionospheric hole generated by the large inland EQ that recently occurred in the Nepal with the magnitude of 7.8 on 25 April 2015.

The extension of ionospheric holes into the tail of Venus

AbstractIonospheric holes are Cytherian nightside phenomena discovered by the NASA Pioneer Venus Orbiter, featuring localized plasma depletions driven by prominent and unexplained enhancements in the draped interplanetary magnetic field. Observed only during solar maximum, the phenomenon remains unexplained, despite their frequent observation during the first 3 years of the mission and more than 30 years having elapsed since their first description in the literature. We present new observations by the European Space Agency Venus Express showing that ionospheric holes can extend much further into the tail than previously anticipated (1.2 to 2.4 planetary radii) and may be observed throughout the solar cycle and over a wide range of solar wind conditions. We find that ionospheric holes are a manifestation of a deeper underlying phenomenon: tubes of enhanced draped interplanetary magnetic field that emerge in pairs from below the ionosphere and stretch far down the tail. We speculate on two possible explanations for the magnetic fields underlying the phenomena: magnetic pileup due to stagnation of ionospheric flow and internal draping around a metallic core.

Ionospheric hole made by the 2012 North Korean rocket observed with a dense GNSS array in Japan

A dense array of Global Navigation Satellite System (GNSS) receivers is useful to study ionospheric disturbances. Here we report observations by a Japanese GNSS array of an ionospheric hole, i.e., localized electron depletion, made by water vapor molecules in the exhaust plume of the second-stage engine of the Unha-3 rocket launched from North Korea, on 12 December 2012. The Russian GNSS was used for the first time to observe such an ionospheric hole. The hole emerged ~6 min after the launch above the middle of the Yellow Sea, and its size and depth suggest that the Unha-3 is slightly less powerful than the 2009 Taepodong-2 missile, also from North Korea. Smaller-scale electron depletion signatures appeared ~10 min after the launch above the southern East China Sea, which is possibly caused by the exhaust plume of the third-stage engine.

Preseismic ionospheric electron enhancements revisited

AbstractPossible enhancement of ionospheric Total Electron Content (TEC) immediately before the 2011 Tohoku‐oki earthquake (Mw9.0) has been reported by Heki (2011). Critical responses to it often come in two stages; they first doubt the enhancement itself and attribute it to an artifact. Second (when they accept the enhancement), they doubt the significance of the enhancement among natural variability of space weather origin. For example, Kamogawa and Kakinami (2013) attributed the enhancement to an artifact falsely detected by the combined effect of the highly variable TEC under active geomagnetic condition and the occurrence of a tsunamigenic ionospheric hole. Here we closely examine the time series of vertical TEC before and after the 2011 Tohoku‐oki earthquake. We first demonstrate that the tsunami did not make an ionospheric hole, and next confirm the reality of the enhancement using data of two other sensors, ionosonde and magnetometers. The amplitude of the preseismic TEC enhancement is within the natural variability, and its snapshot resembles to large‐scale traveling ionospheric disturbances. However, distinction could be made by examining their propagation properties. Similar TEC anomalies occurred before all the M ≥ 8.5 earthquakes in this century, suggesting their seismic origin.

Is an ionospheric electron enhancement preceding the 2011 Tohoku‐Oki earthquake a precursor?

Heki [2011] reported that the TEC gradually enhanced from 40 minutes before the 2011 M9.0 off the Pacific coast of Tohoku earthquake (Tohoku EQ) to the time when the co‐seismic acoustic wave reached the ionosphere and the TEC immediately recovered at the normal state. This paper shows an alternative interpretation of total electron content (TEC) variation in the ionosphere associated with the Tohoku EQ. Our interpretation is that a tsunamigenic ionospheric hole, a wide depletion of the TEC, occurred after the co‐seismic acoustic wave reached the ionosphere and gradually recovered at the normal state with several tens of minutes [Kakinami et al., 2012]. The difference between Heki [2011] and Kakinami et al. [2012] is attributed to the reference curves of the TEC to extract the ionospheric variations. The former is given by the least‐squares fitting curve of the EQ day data excluding an expected precursor period, while the latter is given by the data of the similar orbit of global positioning system (GPS) satellite on another day. The results suggest that variation of slant TEC is explained by the depletion of TEC due to tsunami rather than the precursory enhancement.

Ionospheric disturbances produced by chemical releases at different release altitudes

As one of important and effective means for modifying the ionosphere, releases of neutral gases including H2O, CO2, H2, SF6, etc. can produce artificial ionospheric holes. In this paper, the ionospheric disturbances produced under various release conditions, including use of different release species (H2O and SF6), different release altitudes, and different amounts of released substance, are investigated based on an improved three-dimensional chemical release dynamics model which includes neutral gas diffusion, chemical reaction and the ambipolar diffusion of the plasma. The effects of release altitudes and release amount on ionospheric disturbances, morphology and the dynamics of ionospheric hole are studied. Furthermore, the results are also briefly discussed.

Experimentally investigate ionospheric depletion chemicals in artificially created ionosphere

A new approach for investigating ionosphere chemical depletion in the laboratory is introduced. Air glow discharge plasma closely resembling the ionosphere in both composition and chemical reactions is used as the artificially created ionosphere. The ionospheric depletion experiment is accomplished by releasing chemicals such as SF6, CCl2F2, and CO2 into the model discharge. The evolution of the electron density is investigated by varying the plasma pressure and input power. It is found that the negative ion (SF6−, CCl2F2−) intermediary species provide larger reduction of the electron density than the positive ion (CO2+) intermediary species. The negative ion intermediary species are also more efficient in producing ionospheric holes because of their fast reaction rates. Airglow enhancement attributed to SF6 and CO2 releases agrees well with the published data. Compared to the traditional methods, the new scheme is simpler to use, both in the release of chemicals and in the electron density measurements. It is therefore more efficient for investigating the release of chemicals in the ionosphere.

Tsunamigenic ionospheric hole

Traveling ionospheric disturbances generated by an epicentral ground/sea surface motion, ionospheric disturbances associated with Rayleigh‐waves as well as post‐seismic 4‐minute monoperiodic atmospheric resonances and other‐period atmospheric oscillations have been observed in large earthquakes. In addition, a giant tsunami after the subduction earthquake produces an ionospheric hole which is widely a sudden depletion of ionospheric total electron content (TEC) in the hundred kilometer scale and lasts for a few tens of minutes over the tsunami source area. The tsunamigenic ionospheric hole detected by the TEC measurement with Global Position System (GPS) was found in the 2011 M9.0 off the Pacific coast of Tohoku, the 2010 M8.8 Chile, and the 2004 M9.1 Sumatra earthquakes. This occurs because plasma is descending at the lower thermosphere where the recombination of ions and electrons is high through the meter‐scale downwelling of sea surface at the tsunami source area, and is highly depleted due to the chemical processes.

Seismo-Tsunamigenic Ionospheric Hole Triggered by M 9.0 2011 off the Pacific Coast of Tohoku Earthquake

Giant earthquake and tsunami widely disturbed ionospheric plasma via acoustic gravity waves. During the M 9.0 2011 off the Pacific coast of Tohoku earthquake, the ionospheric disturbances were generated by co-seismic epicentral ground/sea surface motion, Rayleigh-wave traveling, and tsunami-wave traveling. In addition, seismo-tsunamigenic ionospheric hole, widely sudden depression of ionospheric total electron content, was observed. The ionospheric hole gradually disappeared within roughly a few tens minutes.

Ionospheric disturbances produced by chemical releases and the resultant effects on short-wave ionospheric propagation

[1] As an effective means to actively modify the ionosphere, chemical releases can produce artificial ionospheric holes as a consequence of ionization reduction, which can have a great impact on radio wave propagation. To investigate the morphology control of ionospheric holes by various chemical releases and the resultant effects on radio wave propagation, a quantitative numerical model is developed on the basis of the approximate solutions of the diffusion equation of single-point release in uniform atmosphere. While single-point release produces ellipsoidal ionospheric holes, multipoint release can produce other types of ionospheric holes (such as parabola-like tubular ones), which is strongly dependent on changes in the release species, release altitude, and mass of released neutral gas. Releases of both H2O and SF6 can produce ionospheric holes with a similar spatial extent, but the latter tends to result in clearer boundaries and more pronounced electron density reductions. In addition, either an increase in released amount or releases at higher altitudes can lead to a broader hole. To evaluate the effects of an ionospheric hole on radio wave propagation, three-dimensional ray tracing simulations are performed. The ellipsoidal ionospheric holes can act as a lens focusing and bending radio waves, leading to multiple wave reflections inside the holes. In contrast, in the paraboloid tubular ionospheric holes, the rays can penetrate the disturbed region or reflect back, showing a strong dependence on radio frequency. It is well demonstrated that chemical releases can efficiently give rise to artificial ionospheric disturbances and thus modify ionospheric propagation of radio waves.

Radio wave propagation effects produced by chemical releases in the ionosphere

As an effective means to actively modify the ionosphere, chemical release can produce artificial ionospheric holes as a consequence of ionization depletion, which can greatly impact on radio wave propagation. In this paper, on the basis of the pre-study results on ionospheric disturbances produced by some representative chemical releases, the radio waves propagation effects of ionospheric holes that are produced by two different release species, water (H2O) and sulfur hexafluoride (SF6), had been investigated and simulated by the three-dimensional (3-D) numerical ray tracing. The results show that ➀ the appearance of various artificial ionospheric holes can lead to certain decrease of critical frequency in the ionosphere, and ➁ when the wave frequency exceeds the critical frequency, the rays should be multiple reflections or penetrate through the ionospheric hole and focus afterwards with the focus altitude elevated for higher frequencies. This work may provide the necessary theoretical support for chemical release experiments and the evaluation of radio wave propagation effects.

Morphological control of artificial ionospheric hole and its short-wave propagation effects

As one of important and effective means for modifying the ionosphere, chemical release can produce artificial ionospheric holes attributed to ionization depletion, which also greatly affect the short-wave propagation. In this paper, a neural gas multi-point release dynamics model is proposed baseed on mono-point one, and then the morphological control effects of chemical substances, releasing altitude, releasing mode and mass on artificial ionospheric hole are discussed. Furthermore, the short-wave propagation effect of artificial ionospheric hole is simulated and investigated by the 3-D numerical ray tracing.

Ionospheric holes made by ballistic missiles from North Korea detected with a Japanese dense GPS array

A dense array of global positioning system (GPS) receivers is a useful tool to study ionospheric disturbances. Here we report observations by a Japanese GPS array of ionospheric holes, i.e., localized electron depletion. They were made by neutral molecules in exhaust plumes (e.g., water) of ballistic missiles from North Korea, Taepodong‐1 and ‐2, launched on 31 August, 1998, and 5 April, 2009, respectively. Negative anomaly of electron density emerged ∼6 min after the launches in the middle of the Japan Sea, and extended eastward along the missile tracks. By comparing the numerical simulation of electron depletion and the observed change in ionospheric total electron content, we suggest that the exhaust plumes from the Taepodong‐2 second stage effused up to ∼1.5 × 1026 water molecules per second. The ionospheric hole signature was used to constrain the Taepodong‐2 trajectory together with other information, e.g., coordinates of the launch pad, time and coordinates of the first stage splashdown, and height and time of the second stage passage over Japan. The Taepodong‐2 is considered to have reached the ionospheric F region in ∼6 min, flown above northeastern Japan ∼7 min after the launch, and crashed to the Pacific Ocean without attaining the first astronautical velocity. The ionospheric hole in the 1998 Taepodong‐1 launch was much less in size, but it is difficult to compare directly the thrusts of the two missiles due to uncertainty of the Taepodong‐1 trajectory.

Asymmetry of the Venus nightside ionosphere: Magnus force effects

A study of the dawn–dusk asymmetry of the Venus nightside ionosphere is conducted by examining the configuration of the ionospheric trans-terminator flow around Venus and also the dawn-ward displacement of the region where most of the ionospheric holes and the electron density plateau profiles are observed (dawn meaning the west in the retrograde rotation of Venus and that corresponds to the trailing side in its orbital motion). The study describes the position of the holes and the density plateau profiles which occur at neighboring locations in a region that is scanned as the trajectory of the Pioneer Venus Orbiter (PVO) sweeps through the nightside hemisphere with increasing orbit number. The holes are interpreted as crossings through plasma channels that extend downstream from the magnetic polar regions of the Venus ionosphere and the plateau profiles represent cases in which the electron density maintains nearly constant values in the upper ionosphere along the PVO trajectory. From a collection of PVO passes in which these profiles were observed it is found that they appear at neighboring positions of the ionospheric holes in a local solar time (LST) map including cases where only a density plateau profile or an ionospheric hole was detected. It is argued that the ionospheric holes and the density plateau profiles have a common origin at the magnetic polar regions where plasma channels are formed and that the density plateau profiles represent crossings through a friction layer that is adjacent to the plasma channels. It is further suggested that the dawn–dusk asymmetry in the position of both features in the nightside ionosphere results from a fluid dynamic force (Magnus force) that is produced by the combined effects of the trans-terminator flow and the rotational motion of the ionosphere that have been inferred from the PVO measurements.

Ionospheric hole behind an ascending rocket observed with a dense GPS array

Abstract An ascending liquid-fuel rocket is known to make a hole in the ionosphere, or localized electron depletion, by leaving behind large amounts of neutral molecules (e.g. water) in the exhaust plume. Such a hole was made by the January 24, 2006 launch of an H-IIA rocket from Tanegashima, Southwestern Japan, and here we report its observation with a dense array of Global Positioning System receivers as a sudden and temporary decrease of total electron content. The observed disturbances have been compared with a simple numerical model incorporating the water diffusion and chemical reactions in the ionosphere. The substantial vanishing of the ionosphere lasted more than one hour, suggesting its application as a window for ground-based radio astronomical observations at low frequencies.

Are plasma depletions in Saturn's ionosphere a signature of time‐dependent water input?

Recent radio occultation measurements by the Cassini spacecraft reveal the presence of numerous “ionospheric holes”, or plasma depletions, in Saturn's upper atmosphere that cannot be explained with standard photochemical theory. The holes are remarkably similar in size and shape to artificially‐created depletions first observed in the terrestrial ionosphere during the 1970s. At Earth, such vertical structures are typically caused by the enhanced loss of electrons and ions resulting from the introduction of spacecraft exhaust products (e.g., H2O) into the atmosphere. Using a new model of Saturn's upper atmosphere, we show that a time‐variable influx of water into Saturn's ionosphere could explain the observed plasma depletions. The required influxes present a target to assess for the possible sources and consequences of water processes throughout the Saturnian system.