Detection Of Electro-Magnetic Emissions Transmitted From Earthquake Regions Research Articles

Statistical Research on Seismo-Ionospheric Ion Density Enhancements Observed via DEMETER

In this paper, in order to investigate the correlation between seismic activity and ionospheric density variation, nighttime ion density (Ni) data from IAP onboard the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite from 2005 to 2010 are used to carry out statistical analysis. Only data with kp ≤ 3 are selected to avoid density perturbations due to magnetic activity. The aftershocks are also carefully removed. The earthquake-related data were further strictly screened, and the apparent position of anomalies were normalized using Dobrovolsky’s radius. Real and pseudorandom earthquakes are compared and analyzed. The statistical results show that the postseismic effect is obvious; the Ni enhancements are more focused 3–5 days, 9–10 days, and 13–14 days before the earthquake; as the magnitude of earthquake increases, the apparent range and intensity of the ion density enhancements is also increased; and for medium–strong earthquakes, the position of disturbance will exceed Dobrovolsky’s radius.

Complex analysis of the ionosphere variations during the geomagnetic storm at 20 January 2010 performed by Detection of Ionosphere Anomalies (DIA) software and DEMETER satellite data

Abstract. The Detection of Ionosphere Anomalies (DIA) software was developed and used for ionosphere research in the Institute of Space Technique and Technology of the National Center of Space Research and Technology (Almaty, Republic of Kazakhstan). The software was designed for ionosphere anomalies detection, identification, and analysis from satellite spectral and wave data from scientific payloads installed on the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite. The main task of DIA software is to provide the researcher with a convenient package for detection and identification of the sources of electromagnetic radiation, variations of the ionic and electronic components of the ionosphere, and other ionosphere parameters from satellite data. Using this software, a complex research of the state of the medium-latitude ionosphere during a geomagnetic storm on 20 January 2010 was done. Electric and magnetic components of the field in ultralow frequency (ULF), extremely low frequency (ELF), and very low frequency (VLF) bands are processed and analyzed, as well as temperature, velocity, and density of ionic and electronic plasma components and fluxes of energetic electrons at satellite altitude during a storm.

Ionospheric anomalies related to strong earthquakes in North America as observed by TEC

Research studies have recently illustrated a plausible relationship between seismic activity and ionospheric disturbances. To elucidate seismo-ionospheric disturbances, we analyzed the temporal and spatial characteristics of ionospheric disturbances associated with large earthquakes that occurred in North America. We selected two strong events with M ≥ 6.5 that took place in 2009 and 2010 during the solar minimum. We used the United States total electron content (US-TEC) measurements as a main dataset, and the changes in the TEC were compared with the variations in the topside plasma density measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite. Positive or negative TEC anomalies were observed before (as a precursor) and after the earthquakes. In addition, we found that positive anomalies occurred more frequently than negative ones. Although TEC anomalies occurred at all local times, strong anomalies usually appeared from late afternoon to dawn (16–6 local time). Seismic activity-related TEC anomalies were typically limited to the earthquake region, whereas geomagnetic activity-related TEC anomalies were observed over a vast region. Furthermore, local TEC anomalies occurred over a long period of 20 days preceding and succeeding the earthquakes, in contrast to those associated with geomagnetic activities which occurred concurrently with the geomagnetic disturbances. Additionally, most abnormal increments in the electron density obtained by the DEMETER satellite over the seismic zone coincided with the TEC anomalies. Thus, the variations observed in the TEC and topside electron density before and after these two earthquakes suggest that these ionospheric disturbances are related to seismic activities.

Mesoscale convective systems as a source of electromagnetic signals registered by ground-based system and DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite

Abstract. Mesoscale convective systems (MCSs) are especially visible in the summertime when there is an advection of warm maritime air from the west. Advection of air masses is enriched by water vapour, the source of which can be found over the Mediterranean Sea. In propitious atmospheric conditions, and thus significant convection, atmospheric instability or strong vertical thermal gradient leads to the development of strong thunderstorm systems. In this paper, we discuss one case of MCSs, which generated a significant amount of +CG (cloud-to-ground), −CG and intracloud (IC) discharges. We have focused on the ELF (extremely low frequency; < 1 kHz) electromagnetic field measurements, since they allow us to compute the charge moments of atmospheric discharges. Identification of the MCSs is a complex process, due to many variables which have to be taken into account. For our research, we took into consideration a few tools, such as cloud reflectivity, atmospheric soundings and data provided by PERUN (Polish system of the discharge localisation system), which operates in a very high frequency (VHF) range (113.5–114.5 MHz). Combining the above-described measurement systems and tools, we identified a MCS which occurred in Poland on 23 July 2009. Furthermore, it fulfilled our requirements since the thunderstorm crossed the path of the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) overpass.

Seismic influence on the VLF transmitter signal intensity measured by the low-altitude satellite DEMETER

We present results of a statistical study of a possible influence of the seismic activity on the intensity of very low frequency (VLF) transmitter signals observed by a low-altitude satellite. Electric field measurements performed by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite during its entire mission spanning almost 6.5 years were used. Among various VLF transmitter signals detected, we focused particularly on the NWC and JJI transmitters, because of their favorable locations close to seismically active areas. We evaluate the intensities of the detected transmitter signals at the times when they passed in the vicinity of an imminent earthquake during the propagation in the Earth-ionosphere waveguide, and we statistically compare them with the intensities measured at the times when there was no earthquake present. Only earthquakes with magnitudes larger than or equal to 5 and depths shallower than or equal to 40 km were considered in the analysis. Moreover, due to the low intensity of detected transmitter signals during the day, the analysis is limited exclusively to the nightside. Although the amount of relevant data is rather low, the obtained results show that there is a decrease of the detected intensity shortly (0–3 hours) after the times of the main shocks observed both for the NWC and JJI transmitter signals. The effect is spatially rather limited, observed when the signal passes within about 4 degrees from the earthquake epicenter. The intensity decrease appears to be consistent with acoustic-gravity waves propagating from the earthquake region and influencing the bottom of the ionosphere.

Primary Joint Statistical Seismic Influence on Ionospheric Parameters Recorded by the CSES and DEMETER Satellites

AbstractOppositely to a previous statistical work using a single time resolution of the total ion density measured onboard the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite, this work deals with statistical seismo‐ionospheric influences by comparing different parameters and various time resolutions. The O+ density and electron density recorded by the China Seismo‐Electromagnetic Satellite (CSES) for more than one year and by the DEMETER satellite for about 6.5 years have been utilized to globally search ionospheric perturbations with different time resolutions. A comparison is automatically done by software between the occurrence of these ionospheric perturbations determined by different data sets, and the occurrence of earthquakes under the conditions that these perturbations occur at less than 1,500 km and up to 15 days before the earthquakes. Combined with statistical results given by both satellites, it is shown that the detection rate r of earthquakes increases as the data time resolution and the earthquake magnitude increase and as the focal depth decreases. On average, the number of perturbations is higher the day of the earthquake, and then smoothly decreases the days before, which is independent of either ionospheric parameters or time resolutions. The number of right alarms is high near the South Atlantic Magnetic Anomaly area but its relationship with seismic activities is weak. The ion density tends to be more sensitive to seismic activities than the electron density but this needs further investigations. This study shows that the CSES could effectively register ionospheric perturbations due to strong EQs as the DEMETER satellite does.

Possible ionospheric anomalies associated with the 2009 Mw 6.4 Taiwan earthquake from DEMETER and GNSS TEC

The recent advances in satellite based ionosphere monitoring provided more evidence about earthquake (EQ) precursors from lithosphere ionosphere coupling mechanism. In this paper, we investigate ionospheric anomalies associated with the December 19, 2009, Taiwan EQ (Mw = 6.4), that occurred on UT = 13:02 h. Seismo ionospheric anomalies are evaluated during 31 days (20 day before followed by 10 days after the EQ) in the data of French Satellite Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and validated from Global Navigation Satellite System (GNSS) retrieved Total Electron Content (TEC). The day time values of ISL (Langmuir Probe) and IAP (Ion Analyzer) from DEMETER point to significant ionospheric perturbations within 5 days associated with EQ day. Moreover, GNSS stations of International GNSS Service (IGS) within EQ preparation zone also validate anomalies in ionosphere prior/after the Mw 6.4, Taiwan EQ. Moreover, spatial and temporal analyses of daily ionospheric indices from DEMETER and GNSS point to simultaneous enhancement in electron density, ion density, electron temperature and TEC related to the main shock during quiet geomagnetic storm (Dst < − 30 nT, Kp ≤ 3). All these evidence aids in promoting the lithosphere- ionosphere coupling over the epicenter of Mw 6.4 during the preparation period from DEMETER and GNSS TEC.

Long‐Term Variations of Quasi‐Trapped and Trapped Electrons in the Inner Radiation Belt Observed by DEMETER and SAMPEX

AbstractElectrons in the Earth's radiation belts can be categorized into three populations: precipitating, quasi‐trapped, and trapped. We use data from the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and Solar, Anomalous, and Magnetospheric Particle Explorer satellite (SAMPEX) missions and from ground‐based neutron monitors (NM) and sunspot observations to investigate the long‐term variation of quasi‐trapped and trapped sub‐MeV electrons on different L shells in the inner belt. DEMETER and SAMPEX measurements span over 17 years and show that at L ≤ 1.14 the electron flux is anticorrelated with sunspot number, but proportional to the cosmic ray intensity represented by NM count rates, which suggests that electrons at the inner edge of the inner belt are produced by Cosmic Ray Albedo Neutron Decay (CRAND). The solar cycle variation of cosmic rays increased the electron flux at L ≤ 1.14 by a factor of 2 from solar maximum at 2001 to solar minimum at 2009. At L ≥ 1.2, both quasi‐trapped and trapped electrons are enhanced during geomagnetic storms and decay to a background level during extended quiet times. At L &gt; 2, quasi‐trapped electrons resemble trapped electrons, with correlation coefficients as high as 0.97, indicating that pitch angle scattering is the dominant process in this region.

Low-altitude frequency-banded equatorial emissions observed below the electron cyclotron frequency

Abstract. The ICE (Instrument Champ Électrique) experiment on board the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite recorded frequency-banded wave emissions below the electron cyclotron frequency, with band spacing ≳ frequency low-hybrid resonance, in the vicinity of the magnetic equatorial plane. Those radiations were observed in the beginning of the year 2010 on the night side of Earth and rarely on the day side. We distinguish two components: one appears as frequency bands continuous in time between a few kilohertz and up to 50 kHz, and the other one is from 50 to 800 kHz. The first component exhibits positive and negative frequency drift rates in the Southern Hemisphere and Northern Hemisphere, at latitudes between 40 and 20∘. The second one displays multiple spaced frequency bands. Such bands mainly occur near the magnetic equatorial plane with a particular enhancement of the power level when the satellite latitude is close to the magnetic equatorial plane. We show in this study the similarities and the discrepancies between the non-free-space DEMETER frequency-banded emissions and the well-known free-space terrestrial kilometric radiation. The hollow cones of the DEMETER frequency-banded wave emissions are oriented towards Earth's ionosphere. We suggest that the source region is localized in regions poleward of the plasmapause where the ratio of the plasma frequency to gyro-frequency is smaller than one.

Spectral Broadening of NWC Transmitter Signals in the Ionosphere

AbstractIn this study, we use about 6.5 years of observation of Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite to study the spectral broadening of NWC ground transmitter signals and examine key parameters that control the width and intensity of the broadening power. First, we analyze a typical spectral broadening event, with enhanced wave intensity between lower hybrid resonance frequency and NWC signal frequency (19.8 kHz). The width and intensity of broadening power are positively proportional to the NWC wave amplitude. A following statistical analysis reveals a similar dependence on the NWC wave amplitude. The statistical analysis also indicates a significantly negative correlation of broadening spectral intensity and width with the background plasma density. The observations are consistent with existing theories predicting that lower plasma density drives a lower threshold for spectral broadening.

Ionospheric induced plasma disturbances afore the m7.9 eastern Sichuan china earthquake of 12th may, 2008

A great number of earthquakes occur yearly in different areas and almost 100 -120 of them have a magnitude above 5. These seismic activities are very harmful for the inhabitants. Findings reveal that this seismo-electro-magnetic abnormality is a mirror image of some processes, which originated a few weeks before the main event and stay until few days after it. Plasma ion analyser (IAP) and Instrument Sonde de Langmuir (ISL) sensors) experiments available on Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) and Total Electron Content (TEC) from Global Positioning System (GPS) satellites, were employed to study the variations of electron and ion density for ionospheric disturbances before the M7.9 Eastern Sichuan China earthquake of 12th May, 2008. The study revealed seismo-ionospheric induced perturbations exactly three weeks afore the earthquake in all four investigated parameters. Electron density recorded 16.94 cm-3, electron temperature revealed - 2.25 o C while total ion density displayed 6.57 cm-1. The total electron content ranged from 4.28 to 3.6. The disturbance storm time (Dst) and planetary 3-hourly range (Kp) indices were used to classify pre-earthquake anomalies from the other anomalies associated with geomagnetic activities and was seen that this day (-21days relative to the earthquake) was devoid of geomagnetic storm, thus the observed perturbations were seismo-induced but not geomagnetic induced.

Features of Nightside ULF Wave Activity in the Ionosphere

AbstractWe investigate the features of nightside ultralow frequency (ULF) waves in the ionosphere using electric field data in the DC/ULF range observed by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite over a ~5.5‐year period from May 2005 to November 2010. The ULF wave events are recognized by an automatic detection algorithm, and a superposed epoch analysis is performed to study the characteristics of ULF waves during geomagnetic storms. The results show that (1) ULF waves of both nonmagnetospheric and magnetospheric origins occur in the ionosphere; (2) nonmagnetospheric ULF waves present seasonal variations but have no clear response to storms; (3) magnetospheric ULF waves show clear association with the recovery phase of storms but have no obvious seasonal variations; and (4) an interhemispheric asymmetry with higher magnetospheric ULF wave occurrence rate in the Southern Hemisphere particularly around storms can be partly explained by the fact that more of selected isolated storms occurred during summer in the Northern Hemisphere (NH), hence higher conductivity in the NH. However, an analysis of few storms during equinoxes also shows a minor asymmetry. These results still indicate that the ionospheric conductivity in the Southern Hemisphere would be lower than in the NH at nighttime.

Seismo ionospheric anomalies before the 2007 M7.7 Chile earthquake from GPS TEC and DEMETER

Earthquake (EQ) related variations in the ionosphere may provide some insights to understand the seismo ionospheric coupling and to mitigate the damages of seismic hazards. In this paper, the electromagnetic variations in the ionosphere associated with November 14, 2007, M7.7 Chile EQ are investigated in electron density and electron temperature measurements from ISL (Langmuir Probe) of DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite and TEC (total electron content) estimated from GPS (Global Positioning System). The investigation of temporal and spatial measurements suggests anomalies which are observed within 10 days before the future EQ (i.e. 9 days before on November 5, 2007). The temporal values of daytime DEMETER and diurnal TEC on November 5, 2007 imply abrupt anomalies that are considered to be the fragments of the plasma intensification process in the Southern Hemisphere activated by the rock compression in the quake region. Similarly, spatial maps of TEC and DEMETER (electron density and electron temperature) showed the anomalous configuration of the temporal analysis that may induce by the epicenter. In addition to spatial and temporal analysis, the Index number for the northern and southern sectors of the EQ preparation zone around the epicenter along latitude confirmed the anomalous values of electron density and electron temperature of the DEMETER satellite. Similarly, the comparison of electron density and electron temperature at the epicenter latitude and its conjugate reveals anomalous enhancement over the seismogenic zone on November 5, 2007 (9 days before) prior to the event.

Tropospheric and Ionospheric Anomalies Induced by Volcanic and Saharan Dust Events as Part of Geosphere Interaction Phenomena

In this work, we assessed the possible relation of ionospheric perturbations observed by Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER), Global Positioning System total electron content (GPS TEC), National Oceanic and Atmospheric Administration (NOAA)-derived outgoing longwave-Earth radiation (OLR), and atmospheric chemical potential (ACP) measurements, with volcanic and Saharan dust events identified by ground and satellite-based medium infrared/thermal infrared (MIR/TIR) observations. The results indicated that the Mt. Etna (Italy) volcanic activity of 2006 was probably responsible for the ionospheric perturbations revealed by DEMETER on 4 November and 6 December and by GPS TEC observations on 4 November and 12 December. This activity also affected the OLR (on 26 October; 6 and 23 November; and 2, 6, and 14 December) and ACP (on 31 October–1 November) analyses. Similarly, two massive Saharan dust episodes, detected by Robust Satellite Techniques (RST) using Spinning Enhanced Visible and Infrared Imager (SEVIRI) optical data, probably caused the ionospheric anomalies recorded, based on DEMETER and GPS TEC observations, over the Mediterranean basin in May 2008. The study confirmed the perturbing effects of volcanic and dust events on tropospheric and ionospheric parameters. Further, it demonstrated the advantages of using independent satellite observations to investigate atmospheric phenomena, which may not always be well documented. The impact of this increased detection capacity in reducing false positives, in the framework of a short-term seismic hazard forecast based on the study of ionospheric and tropospheric anomalies, is also addressed.

Assessing seismo-ionospheric disturbances using Vanuatu and Honshu earthquakes of March 25, 2007, employing DEMETER and GPS data

The signals of detection of electromagnetic emissions transmitted from earthquake regions (DEMETER), plasma ion analyser, instrument Sonde de Langmuir sensors, global positioning system and total electron content (TEC) were used to decipher variations of electron and ion density in the neighbourhoods of twin seismic events. These events took place on March 25, 2007, at Vanuatu and Honshu (Japan). Investigations through statistical analysis revealed that ionospheric plasma parameters of electron density and ion density were disturbed on both sets of data on the 6th and 4th days before the Honshu earthquake in Japan, during quiet geomagnetic period. However, for the Vanuatu earthquake, all detected irregularities from DEMETER data occurred during geomagnetic storm. Nevertheless, TEC anomaly showed unusual variations exactly two weeks before the seismic activity on quiet geomagnetic day. The disturbance storm time and planetarische Kennziffer indices were engaged in isolating pre-earthquake irregularities from other irregularities associated with geomagnetic actions.

Stepping into the Equatorward Boundary of the Auroral Oval: preliminary results of multi scale statistical analysis

This work aims at showing how analysis techniques, designed to highlight the multi−scale structure of a signal, may be of help in de− scribing fluctuations of the ionospheric medium. In particular, the technique used here is the ALIF (Adaptive Local Iterative Filter). We have applied ALIF to the characterisation of plasma irregularities in the equatorward boundary of the auroral oval. The data used are from the LEO satellite DEMETER (Detection of Electro−Magnetic Emissions Transmitted from Earthquake Regions) while it crosses the Equatorward boundary of the oval. The time series analysed are those from the electric field instrument ICE (Instrument de Champ Electrique) on board of DEMETER, and the identification of the equatorward boundary in the time series of in situ data is based on the comparison between the satellite trajectory and the picture of the auroral oval from the simultaneous auroral imaging by the DMSP satellite. In detail, we pre− sent an analysis of the multi−scale features and dynamics of ionospheric plasma along the DEMETER trajectory in different regions, which seem to be characterized by plasma irregularities of different nature. A clear change of the multi−scale nature of plasma fluctuations is observed in the correspondence of the irregularities originated by particle precipitation in the equatorward boundary of the auroral oval.

Cosmic Ray Albedo Neutron Decay (CRAND) as a Source of Inner Belt Electrons: Energy Spectrum Study

AbstractCosmic Ray Albedo Neutron Decay (CRAND) has been recently confirmed as a source of energetic electrons at the inner edge of the inner belt by the Colorado Student Space Weather Experiment (CSSWE) mission. Here we use observations from the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) mission, to investigate the CRAND contribution to inner belt electrons quantitatively over a broad energy range (~100–800 keV). Spectral fitting analysis supports the conclusion that CRAND is the most important electron source at the inner edge of the inner belt. For the first time, we show that CRAND is the dominant source of &gt;250‐keV quasitrapped electrons throughout the inner belt and slot region during quiet times. We suggest that additional sources for &lt;250‐keV electrons exist, perhaps from inward transport. In contrast, dynamics of electrons in the inner belt and slot region is dominated by injections during active times.

Selective Attenuation of Lightning‐Generated Whistlers at Extralow Frequencies: DEMETER Spacecraft Observations

AbstractFrequency‐time spectrograms measured by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) spacecraft (2004–2010, altitude about 700 km) at frequencies below 20 kHz sometimes contain lightning‐generated whistlers whose intensity is significantly reduced at specific frequencies. The frequencies of the reduced intensity vary smoothly over the event duration, forming apparent curves in frequency‐time spectrograms. Events at frequencies higher than the Earth‐ionosphere waveguide cutoff frequency were explained by the interference of the first few waveguide modes of lightning‐generated spherics propagating therein (Záhlava et al., 2015, https://doi.org/10.1002/2015JA021607. Here we present an analysis of events observed at frequencies lower than about 1 kHz. Altogether, we analyze 263 events identified at the times when DEMETER operated in the burst mode. The vast majority of the events (95%) took place during the nighttime, and they occurred more frequently during spring/autumn than during winter/summer. We present an overview of event properties. Moreover, measurements of all six electromagnetic field components performed by DEMETER allow us to perform a detailed wave analysis. It is shown that the emissions propagate with high wave normal angles inclined toward the Earth. We suggest that the events might be due to the wave propagation in the ionospheric waveguide formed around the refractive index maximum at the altitude of about 105 km.

The Midlatitude Trough and the Plasmapause in the Nighttime Ionosphere Simultaneously Observed by DEMETER During 2006–2009

AbstractThis paper concurrently investigates the midlatitude trough and the plasmapause positions in the ionosphere by colocated measurements of the electron density, electron temperature, and whistler count probed by DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions) satellite in the nighttime at 2230 LT (local time; 1900–0100 MLT, magnetic local time, mainly in the premidnight period) during the 4‐year period of 2006–2009. More than 13,000 Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions orbits of the electron density and the electron temperature are used to search the trough position, while the same amount of the whistler count is employed to determine the plasmapause position at the satellite altitude. The plasmapause is more sensitive to solar activity, which moves equatorward 1.0–1.2° form the low to high solar activity of the study period. On the other hand, the midlatitude trough is more sensitive to seasonal variation, which shifts poleward 1.7–2.5° from the winter to summer month in the study period. The midlatitude trough usually appears in the poleward side of the plasmapause during the study period. Both of the midlatitude trough and the plasmapause move equatorward during the magnetic disturbed condition. For the magnetic disturbed Kp ≥ 6−, the midlatitude trough can appear in the equatorward side of the plasmapause.

On the Origin of Ionospheric Hiss: A Conjugate Observation

AbstractWe present a conjugate observation on whistler mode electromagnetic hiss from the low Earth orbit satellite Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and the high‐altitude elliptical orbit spacecraft Time History of Events and Macroscale Interactions during Substorms (THEMIS). The conjugate observation was performed at 14:51:10 to 15:12:00 UT on 15 June 2010, when DEMETER was flying across the L shell region from ~1.39 to 2.80 at an altitude of ~660 km; meanwhile, THEMIS probes were passing through the L shell region from ~1.64 to 1.91 at altitudes from ~1.6 to 2.0 RE. The conjugated observations demonstrate similar time‐frequency structures between the ionospheric hiss (~350 to 800 Hz) captured by DEMETER and the plasmaspheric hiss (~350 to 900 Hz) recorded by THEMIS probes, including similar peak frequencies (~500 to 600 Hz), similar lower cutoff frequencies (~350 to 400 Hz), and upper cutoff frequencies (~730 to 800 Hz). The wave vector analyses show that the ionospheric hiss propagates obliquely downward to the Earth and slightly equatorward with right‐handed polarization, suggesting that its source comes from higher altitudes. Ray tracing simulations with the constraint of observations verify that the connection between ionospheric and plasmaspheric hiss is physically possible through wave propagation. This study provides direct observational evidence to support the mechanism that high‐altitude plasmaspheric hiss is responsible for the generation of low‐altitude ionospheric hiss.