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

Ionospherically reflected proton whistlers

AbstractWe present experimental observations and detailed investigation of the variety of proton whistlers that includes transequatorial and ionospherically reflected proton whistlers. The latter have previously been indicated from numerical modeling of spectrograms. The study is based on six‐component ELF wave data from the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite which permits to obtain not only spectrograms displaying the power spectral density but also such wave properties as the polarization, wave normal angle, wave refractive index, and normalized parallel component of the Poynting vector. The explanation of various types of proton whistlers is based on the properties of ion cyclotron wave propagation in a multicomponent magnetoplasma, with special consideration of the effect of ion hybrid resonance reflection. Analysis of experimental data is supplemented by numerical modeling of spectrograms that reproduces the main features of experimental ones. As a self‐contained result, we provide conclusive experimental evidences that the region illuminated by a lightning stroke in the Earth‐ionosphere waveguide may spread over a distance of 4000 km in both hemispheres.

Seismo-ionospheric precursory anomalies detection from DEMETER satellite data based on data mining

Widespread researches and studies on earthquake prediction show that seismo-ionospheric disturbances can be observed over seismic regions before an earthquake. However, it is still hard to detect accurate pre-seismic ionosphere anomaly and use them to predict earthquake. To solve the problem, we propose a method that can extract the feature of pre-seismic ionospheric anomalies based on data mining. The main theme of this method can be described as follows: First, we mine frequent itemsets from pre-seismic ionosphere data measured by DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite and regard them as seismic features after a series of processing; then we carry out earthquake prediction experiments in test region to check the validity of these features as well as searching for interesting information. The experimental results reveal that this method is effective, and we also get some remarkable conclusions about earthquake prediction, such as the features of pre-seismic ionosphere anomalies contain ion temperature, electron density, electron temperature and plasma potential and among all the experimental conditions we discussed in this paper, and features mined from ionosphere data 5 days before earthquake lead to the highest accuracy in earthquake prediction.

Statistical investigation of VLF quasiperiodic emissions measured by the DEMETER spacecraft

AbstractWe present a survey of quasiperiodic (QP) ELF/VLF emissions detected onboard the DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions) satellite (altitude of about 700 km, nearly Sun‐synchronous orbit at 10:30/22:30 LT). Six years of data have been visually inspected for the presence of QP emissions with modulation periods higher than 10 s and with frequency bandwidths higher than 200 Hz. It is found that these QP events occur in about 5% of daytime half orbits, while they are basically absent during the night. The events occur predominantly during quiet geomagnetic conditions following the periods of enhanced geomagnetic activity. Their occurrence and properties are systematically analyzed. QP emissions occur most often at frequencies from about 750 Hz to 2 kHz, but they may be observed at frequencies as low as 500 Hz and as high as 8 kHz. Modulation periods of QP events may range from about 10 to 100 s, with typical values of 20 s. Frequency drifts of the identified events are generally positive, but they are lower for events with larger modulation periods. The events are usually limited to higher L values (L > 2). The upper L shell boundary of their occurrence could not be identified using the DEMETER data, but they are found to extend up to at least L ~ 6. The occurrence rate of the events is significantly lower at the longitudes of the South Atlantic anomaly (by a factor of more than 2).

Seismo‐ionospheric coupling appearing as equatorial electron density enhancements observed via DEMETER electron density measurements

AbstractWe report the processes and results of statistical analysis on the ionospheric electron density data measured by the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite over a period of 6 years (2005–2010), in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one‐dimensional time series analysis between the daily seismic activity indices and the equatorial ionization anomaly (EIA) intensity indices, which represent relative equatorial electron density increase, were performed for each region. The statistically significant values of the lagged cross‐correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 5.0 in the low‐latitude region can accompany observable precursory and concurrent EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo‐ionospheric coupling is consistent with our observation, and the possibility of earthquake prediction using the EIA intensity variation is discussed.

The asymmetrical features in electron density during extreme solar minimum

The variations of plasma density in topside ionosphere during 23rd/24th solar cycle minimum attract more attentions in recently years. In this analysis, we use the data of electron density (Ne) from DEMETER (Detection of Electromagnetic Emissions Transmitted from Earthquake Regions) satellite at the altitude of 660–710km to investigate the solstitial and equinoctial asymmetry under geomagnetic coordinate system at LT (local time) 1030 and 2230 during 2005–2010, especially in solar minimum years of 2008–2009. The results reveal that ΔNe (December–June) is always positive over Southern Hemisphere and negative over northern part whatever at LT 1030 or 2230, only at 0–10°N the winter anomaly occurs with ΔNe (December–June)>0, and its amplitude becomes smaller with the declining of solar flux from 2005 to 2009. The ΔNe between September and March is completely negative during 2005–2008, but in 2009, it turns to be positive at latitudes of 20°S–40°N at LT 1030 and 10°S–20°N at LT 2230. Furthermore, the solstitial and equinoctial asymmetry index (AI) are calculated and studied respectively, which all depends on local time, latitude and longitude. The notable differences occur at higher latitudes in solar minimum year of 2009 with those in 2005–2008. The equinoctial AI at LT 2230 is quite consistent with the variational trend of solar flux with the lowest absolute AI occurring in 2009, the extreme solar minimum, but the solstitial AI exhibits abnormal enhancement during 2008 and 2009 with bigger AI than those in 2005–2007. Compared with the neutral compositions at 500km altitude, it illustrates that [O/N2] and [O] play some roles in daytime and nighttime asymmetry of Ne at topside ionosphere.

Multisatellite observations of an intensified equatorial ionization anomaly in relation to the northern Sumatra earthquake of March 2005

AbstractHere we report multisatellite observations of ionospheric disturbances in relation to the occurrence of the M8.7 northern Sumatra earthquake of 28 March 2005. The DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions) and CHAMP (Challenging Minisatellite Payload) satellite data were investigated to find possible precursory and postevent phenomena. It was found that EIA (equatorial ionization anomaly) strength expressed in the apex height, derived from the CHAMP plasma density profile, was intensified along the orbits whose longitudes were close to the epicenter within about a week before and after occurrence of the earthquake. Increases in electron and O+ density along the orbits close to the epicenter were also observed in the DEMETER measurements. The normalized equatorial plasma density derived from the DEMETER measurements showed intensification about a week before and after the earthquake reaching maximum the day after the shock and afterward disappearing. In addition, similar behavior of the EIA enhancements related to the M8.0 Pisco earthquake of 15 August 2007 was observed. Surveys of space weather and geomagnetic activities excluded the possibility that these fluctuations were caused by changes in space weather or by a geomagnetic storm. Statistical analyses of the longitudinal variation revealed that the EIA was enhanced in the west of the epicenter and reduced in the east of the epicenter, and this fits the “increased conductivity” model. Based on these observations, we proposed a revised view of seismo‐ionospheric coupling in the region of the geomagnetic equator, to explain the EIA features observed in this study.

Solar cycle variation of the electron density in the topside ionosphere at local nighttime observed by DEMETER during 2006–2008

AbstractThe solar cycle variations of electron density (Ne) in the topside ionosphere are presented by observations around local time 22:30 from Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite during 2006–2008 in the low solar activity, in which the revisited orbits are selected to construct Ne time sequences at different points. The results show that electron density (Ne) reduced 50–100% since 2006 to 2008 at equatorial area and middle latitudes, with much bigger maximal Ne in 2006 but even no yearly peak in 2007 and 2008 around 30° latitude. The seasonal asymmetry is revealed by the yearly maxima of Ne in December over Southern Hemisphere always being larger than those in June over Northern Hemisphere. Furthermore, the equinoctial asymmetry is found around the magnetic equator and high northern latitudes under the low solar activity, and the latter one has not been revealed in other research. Ne from IRI2012 is close to the actual observation by DEMETER in 2008, even better than those in 2006 and 2007, indicating the great improvement of this empirical ionospheric model in this extremely low solar minimum. After comparison with the fitted results by indices of F10.7 and EUV combined with the first five periods in Ne, EUV is a little better to describe the variations in Ne during this solar minimum. By discussing the relationship among nighttime Ne and molecules in upper atmosphere, the [O/N2] density ratio is the key factor at high latitude, while [O] density plays a certain role to electron density around the equator.

Irregularities of the ionospheric plasma and the ULF electric components obtained from DEMETER satellite experiments above Chile earthquake (27 February 2010)

The detection of ionospheric disturbances associated with seismic activity is one of the main purposes of the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) micro-satellite. In this view, this study attempts to analyze the problem of detecting these disturbances before an earthquake occurrence and to discuss the Chile earthquake case study. Using ultralow frequency (ULF) measurements of Instrument Champ Electrique (ICE) experiments on board the DEMETER satellite, possible irregularities in this electric component have been investigated in the vicinity of Chile (27 February 2010) earthquake region. The data used in this paper cover the period from 10 to 26 February 2010. The anomalous variations in the calculated ULF electric component in the direction Z of satellite were clearly observed on the 17th, 11th, and 1st days preceding the earthquake. It is noted that the electric component obviously strongly decreased prior to the earthquake. These unusual variations have also been observed in the variation of several plasma parameters recorded by DEMETER directly above the epicenter during the whole period. Hence, the detected anomalies resulting from the ICE ULF waveforms in quiet geomagnetic conditions could be regarded as seismo-ionospheric precursors.

Temporal and spatial analyses on seismo-electric anomalies associated with the 27 February 2010 <i>M</i> = 8.8 Chile earthquake observed by DEMETER satellite

Abstract. This paper studies seismo-electromagnetic anomalies observed by the French satellite DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) during the 27 February 2010 M = 8.8 Chile earthquake. The nighttime electron density (Ne), electron temperature (Te), ion density (Ni), ion temperature (Ti) and whistler counts (Cw) are investigated. A statistical analysis of the box-and-whisker method is applied to see if data of two or more groups under study are significantly different. A cross-examination of temporal variations before and after shows that Ne and Ni (Cw) increases (decreases) appear 10–20 days before the earthquake. A comparison of data over the epicenter and those over its reference area can be employed to discriminate the earthquake-related anomalies from global effects. Results prove that anomalous enhancements of Ne, Ni, and Ti occur specifically around the epicenter area. The intersection of the temporal and spatial results confirms that Ne and Ni are useful and sensitive detecting anomalous related to the 2010 M = 8.8 Chile earthquake.

Determining the spectra of radiation belt electron losses: Fitting DEMETER electron flux observations for typical and storm times

The energy spectra of energetic electron precipitation from the radiation belts are studied in order to improve our understanding of the influence of radiation belt processes. The Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) microsatellite electron flux instrument is comparatively unusual in that it has very high energy resolution (128 channels with 17.9 keV widths in normal survey mode), which lends itself to this type of spectral analysis. Here electron spectra from DEMETER have been analyzed from all six years of its operation, and three fit types (power law, exponential, and kappa‐type) have been applied to the precipitating flux observations. We show that the power law fit consistently provides the best representation of the flux and that the kappa‐type is rarely valid. We also provide estimated uncertainties in the flux for this instrument as a function of energy. Average power law gradients for nontrapped particles have been determined for geomagnetically nondisturbed periods to get a typical global behavior of the spectra in the inner radiation belt, slot region, and outer radiation belt. Power law spectral gradients in the outer belt are typically −2.5 during quiet periods, changing to a softer spectrum of ∼−3.5 during geomagnetic storms. The inner belt does the opposite, hardening from −4 during quiet times to ∼−3 during storms. Typical outer belt e‐folding values are ∼200 keV, dropping to ∼150 keV during geomagnetic storms, while the inner belt e‐folding values change from ∼120 keV to >200 keV. Analysis of geomagnetic storm periods show that the precipitating flux enhancements evident from such storms take approximately 13 days to return to normal values for the outer belt and slot region and approximately 10 days for the inner belt.

Whistler propagation in ionospheric density ducts: Simulations and DEMETER observations

On 16 October 2009, the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite observed VLF whistler wave activity coincident with an ionospheric heating experiment conducted at HAARP. At the same time, density measurements by DEMETER indicate the presence of multiple field‐aligned enhancements. Using an electron MHD model, we show that the distribution of VLF power observed by DEMETER is consistent with the propagation of whistlers from the heating region inside the observed density enhancements. We also discuss other interesting features of this event, including coupling of the lower hybrid and whistler modes, whistler trapping in artificial density ducts, and the interference of whistlers waves from two adjacent ducts.

Modeling energetic electron penetration into the slot region and inner radiation belt

The inner radiation belt is thought to be quite stable, and only the most intense geomagnetic storms can cause energetic electron variations in the slot region and inner belt. In this paper, using energetic electron flux data from Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite, we show that 100s keV electron flux enhancements in the slot region and inner belt are seen quite often and can occur even during moderate geomagnetic storms. In addition, by transforming the energetic electron flux data into the phase space density (PSD), we model the inward radial transport of two different electron populations, μ=30 MeV/G (K=0) and μ=15 MeV/G (K=0), using a 1‐D radial diffusion model in which the radial diffusion coefficient is directly associated with solar wind parameters and L shell. The model results reproduce the PSD data well in the slot region and inner belt, indicating that the flux enhancement in the inner belt and slot region can be well explained by inward radial transport. The radial diffusion coefficients used in our model are much larger than the widely used Kp‐dependent electromagnetic radial diffusion coefficient but are smaller than the Kp‐dependent electrostatic radial diffusion coefficient (Brautigam and Albert, 2000), suggesting that the Kp‐dependent diffusion coefficient cannot be simply extended to lower L region to account for the observed enhancements of energetic electrons in the slot region and inner belt.

Analysis of space- and ground-based parameters prior to an earthquake on 12 December 2009

The present study includes observations of anomalies at ionospheric and ground levels using data from global positioning system (GPS)-based total electron content (TEC), ionospheric electron density by Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER), and ground-based ultra-low-frequency (ULF) emission prior to an earthquake that occurred on 12 December 2009. The analysis of the data from these three different techniques show relations with preseismic activities. The GPS-based TEC showed enhancement three days prior to the day of the earthquake. On converting the satellite azimuth into latitude and longitude, a large number of passes giving anomalous TEC values were observed covering a zone 17–23° N and 70–74° E (i.e. around the epicentre). Electron density and temperature as measured by DEMETER also show enhancement of the tracks around the epicentre one day prior to the earthquake. For ground-based ULF emission, we used different analysis techniques for the detection of abnormal changes in ULF emission before the earthquake. We observed changes in different parameters such as polarization ratio and fractal dimension. Clear enhancement is observed for polarization parameters (Z/X, Z/Y) and fractal analysis (for the Z component). The results provide useful information in acquiring data prior to earthquakes.

Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from preseismic activity

We use VLF electromagnetic wave data measured by the DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions) satellite at an altitude of about 700 km to check for the presence of statistically significant changes of natural wave intensity (due to signals from lightning) related to preseismic activity. All the relevant data acquired by DEMETER during almost 6.5 years of the mission have been analyzed using a robust two‐step data‐processing schema. This enables us to compare data from the vicinity of about 8400 earthquakes with an unperturbed background distribution based on data collected during the whole DEMETER mission and to evaluate the statistical significance of the observed effects. We confirm previously reported results of a small but statistically significant decrease of the wave intensity (by ∼2 dB) at frequencies of about 1.7 kHz. The effect is observed for a few hours before the times of the main shocks; it occurs during the night. The effect is stronger between March and August, at higher latitudes and for the positions of hypocenters below the sea. We suggest an explanation based on changed properties of the lower boundary of the ionosphere, which leads to a decrease of the intensity of lightning‐generated whistlers observed at the spacecraft altitude. This effect might result from a lowering of the ionosphere associated with an increase in the electrical conductivity of the lower troposphere due to an additional ionization of air molecules at the Earth's surface prior to earthquakes.

Attenuation of lightning‐produced sferics in the Earth‐ionosphere waveguide and low‐latitude ionosphere

We compare radio atmospherics (sferics) detected by the World Wide Lightning Location Network (WWLLN) to very low frequency (VLF) whistler waves observed in the low‐latitude ionosphere by the Vector Electric Field Instrument of the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. We also model the propagation of these sferics through the Earth‐ionosphere waveguide to the subsatellite point using the Long‐Wavelength Propagation Capability software and compare this result to the same C/NOFS data set. This unprecedentedly expansive data set allows comparison to theory and prior observation of VLF radio wave propagation in the Earth‐ionosphere waveguide and low‐latitude ionosphere. We show that WWLLN and C/NOFS observe the well‐known effect of variable attenuation with direction within the Earth‐ionosphere waveguide. Propagation within the ionosphere is also examined, and a lack of attenuation above 400 km is observed. Finally, in comparison to recent works using Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) data by Fiser et al. and Chum et al., we find that C/NOFS successfully detects whistlers with comparable amplitudes at much greater distances, compared to those reported for DEMETER.

Seismo-ionospheric anomalies in total electron content of the GIM and electron density of DEMETER before the 27 February 2010 M8.8 Chile earthquake

In this paper we examine the pre-earthquake ionospheric anomalies by the total electron content (TEC) extracted from GIM (global ionospheric map) and the electron density (Ne) observed by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite during the 2010 M8.8 Chile earthquake. Temporal variations show the nighttime TEC and Ne simultaneously increase 9–19 days before the earthquake. A cross-comparison of data recorded during the period of 1 February to 3 March in 2006–2010 confirms the above temporal anomalies specifically appear in 2010. The spatial analyses show that the anomalies tend to appear over the epicenter.

Burst increases of precipitating electrons recorded by the DEMETER satellite before strong earthquakes

Abstract. This case study developed a method for data processing over six years, from 2004 to 2010, of 70 keV–2.3 MeV electrons recorded by the DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite. Short time increases in electron counting rates, having 99% probabilities of not being Poisson fluctuations, were statistically selected using geomagnetic invariant space and called electron bursts. Temporal series were analysed confirming the seasonal variations in low energy bands of 70–450 keV. Differently from previous results, the DEMETER results exhibited two peaks of electron bursts: one in the period June–August and one in the period December–February annually. Specifically, six earthquake cases are presented in detail having increases in electron burst number prior to events. Moreover, electron burst precipitation occurring before each strong earthquake of the entire period over the life of the satellite with M ≥ 7.0 was verified as having a probability greater than 97% of not being of a statistical origin. Low energetic electrons in 70–330 keV resulted occurring more frequently near seismic activity than those observed in 330 keV–2.34 MeV energy bands at the satellite altitude in the ionosphere.

Conjugate observations of quasi‐periodic emissions by Cluster and DEMETER spacecraft

AbstractQuasi‐periodic (QP) emissions are electromagnetic emissions at frequencies of about 0.5–4 kHz that are characterized by a periodic time modulation of the wave intensity. Typical periods of this modulation are on the order of minutes. We present a case study of a large‐scale long‐lasting QP event observed simultaneously on board the DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions) and the Cluster spacecraft. The measurements by the Wide‐Band Data instrument on board the Cluster spacecraft enabled us to obtain high‐resolution frequency‐time spectrograms of the event close to the equatorial region over a large range of radial distances, while the measurements by the STAFF‐SA instrument allowed us to perform a detailed wave analysis. Conjugate observations by the DEMETER spacecraft have been used to estimate the spatial and temporal extent of the emissions. The analyzed QP event lasted as long as 5 h and it spanned over the L‐shells from about 1.5 to 5.5. Simultaneous observations of the same event by DEMETER and Cluster show that the same QP modulation of the wave intensity is observed at the same time at very different locations in the inner magnetosphere. ULF magnetic field fluctuations with a period roughly comparable to, but somewhat larger than the period of the QP modulation were detected by the fluxgate magnetometers instrument on board the Cluster spacecraft near the equatorial region, suggesting these are likely to be related to the QP generation. Results of a detailed wave analysis show that the QP emissions detected by Cluster propagate unducted, with oblique wave normal angles at higher geomagnetic latitudes.

Analysis of GPS-based TEC and electron density by the DEMETER satellite before the Sumatra earthquake on 30 September 2009

An analysis of ionospheric total electron content (TEC) variations obtained using Global Positioning System (GPS) measurements and electron density observations by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER)/ISL before the Sumatra earthquake (magnitude 7.6) on 30 September 2009 is presented. The data used are global TEC maps created in the IONEX format to estimate the spatial scale of ionospheric irregularities associated with this earthquake and DEMETER/ISL observations to analyse plasma parameter changes during earthquakes. This study for the first time integrates ground-based GPS receiver and space-based DEMETER/ISL observations to probe seismo-ionospheric anomalies before a large earthquake. The pre-seismic behaviour of the TEC was detected within a few days before the main event. The anomaly appeared as local TEC enhancement in the vicinity of the forthcoming earthquake epicentre. These structures were generated in the ionosphere at a similar local time at 1, 3 and 5 days prior to the main shock. The equatorial anomaly trough moved northwards (5°) on the earthquake day and 7.5° southwards the next day. The results demonstrate that both enhanced and reduced anomalies in the ionospheric electron density appeared before the Sumatra earthquake. The results from International GNSS Service (IGS) GPS data demonstrate that TEC variations can be used to detect seismo-ionospheric signatures.

Electron Density Perturbation Before the 27 February 2010 Chile M8.8 Earthquake

AbstractBased on the data of France DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions) satellite, we have made identification to the level 1 data using level 2 picture, moving median processing, analyses of latitude changes and spatial differences. We found some anomalies in the ionosphere above the epicenter of the 27 February 2010 Chile M8.8 earthquake. In an area 1500 km apart from the epicenter, electron density rose on 20 February 2010. The electron density declined on 24th. The electric, magnetic fields and some plasma parameters disturbed at the same time on 25th and 26th. Besides, on 26th, electron density of 2 orbits exceeded the background values. The electric field spectrum around the magnetic equator on 27th began to drop 4 hours before the great earthquake, and meanwhile strong perturbations of some plasma parameters occurred.