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The role of solar activity in the growth of an earthquake (EQ) is the topic of study here, focussing on the correlation & distribution function between global EQ events of M ≥ 4.5 and solar parameters covering seven cycles from 18 to 24. The analysis modes are in two steps: (i) EQ events in a total of all cycles taken under study and solar role on their growth; and (ii) EQ events filtered for a High Solar Active (HSA) and a Low Solar Active (LSA) years for each individual cycle & the respective contribution of solar strength to their occurrences. The paper presents the observation by drawing a relation between EQ event ratio during LSA and HSA year, i.e., EQLSA/EQHSA with the corresponding Rz ratio of the years, an approach adopted to reduce any bias/errors that arise on availability of more EQ data as year advances. The analysis offers a negative cum complex distribution with more EQ cases at 60–70% below the peak Rz when strong solar ambiances are observed to inhibit the growth of severe EQ events. The overall correlation analyses between Rz, geomagnetic indices like Kp/DST, and EQ-events of different magnitudes also provided a conclusion that solar ambiances play a complicated role in the growth process of an EQ. These observations are discussed by invoking the Forbush effect along with the possible contribution of atmospheric variabilities like global temperature, lithosphere heat content, and anthropogenic components.

The paper presents atmospheric coupling physics through identifying a few significant features imprinted on the ionosphere by certain unique seismic environments when a number of successive cluster of earthquakes ranging from 7.1 to 8.2 magnitudes occurred within about two weeks period, over the East-West Pacific zone covering 150° E to 70° W. Amongst the cases considered here are earthquakes of Chile Apr. 1, 2014 (M = 8.2) and Apr. 3, 2014 (M = 7.7), New Guinea Apr. 11, 2014 (M = 7.1) and Solomon Islands 13.04.2014 (M = 7.6). The main data source for the study is Global TEC with supplementary inputs from GPS observations taken at Guwahati (26° N, 92° E), an Appleton anomaly crest region. A few EQ events with epicenters in and around this anomaly zone are also taken in the study to focus on the seismic induced density features like Earthquake time Equatorial Anomaly (EEA) and Earthquake time Equatorial Anomaly Crest (EEAC) developed over the belt. Such anomalous modifications in TEC resulting to growths of EEA and EEAC covering Solomon Islands—New Guinea extending up to Chile along the fault lines for more than a month, are significant observations brought out in the paper. The GPS TEC data from Gauhati University are utilized in identifying the epicentre position through anomalous appearance of satellites beyond the Line Of Sight (LOS) observation. Finally, the seasonal role on enhancing the seismic induced E-field coupled by mutual interactive EQ preparatory effects of the three major events as well as in enhancement of EQ time radon emission through fault is invoked in explanation to the anomalous density features.

Malaysia Youth Satellite (MYSat) is a scientific 1U CubeSat initiated by School of Aerospace Engineering Universiti Sains Malaysia (USM) in 2016. The objective of the MYSat mission is to measure accurate electron density and temperature in E-layer of the ionosphere by a CubeSat. This mission was driven from a study which reported that Earthquake precursors could be analyzed from the ionosphere. Electron temperature and density probe (TeNeP) was the selected scientific instrument for MYSat. This instrument develops a technique by measuring the shift of electric floating potential (ΔVf) characteristics of an electrode immersed in plasma. The ΔVf characteristic of the plasma will then be retrieved from the instrument where the plasma’s electron density (ne) together with the temperature (Te) can be acquired. The TeNeP instrument has been proven not affected by the satellite potential variation effects, which is a common problem for electron measurements onboard small satellites, especially CubeSats. Therefore, the accurate Te and ne measured by MYSat could contribute to the on-going research regarding ionospheric physics and possible Earthquake precursor effects. An already developed TeNeP circuit based on a 2U platform has been redeveloped for MYSat’s 1U based platform. In this paper, several performance tests to the TeNeP generator circuit in the preparation of the MYSat will be shown and discussed.

The earthquake (EQ) time coupling processes between equator-low-mid latitude ionosphere are complex due to inherent dynamical status of each latitudinal zone and qualified geomagnetic roles working in the system. In an attempt to identify such process, the paper presents temporal and latitudinal variations of ionization density (foF2) covering 45°N to 35°S, during a number of earthquake events (M > 5.5). The approaches adopted for extraction of features by the earthquake induced preparatory processes are discussed in the paper through identification of parameters like the ‘EQ time modification in density gradient’ defined by δ = (foF2 max − foF2 min)∕τmm, where τmm – time span (in days) between EQ modified density maximum and minimum, and the Earthquake time Equatorial Anomaly, i.e. EEA, one of the most significant phenomenon which develops even during night time irrespective of epicenter position. Based on the observations, the paper presents the seismic time coupling dynamics through anomaly like manifestations between equator, low and mid latitude ionosphere bringing in the global Total Electron Content (TEC) features as supporting indices.

The electron density and temperature probe (EDTP) was proposed by Oyama and others instead of a Langmuir probe that is the conventional measurement tool of an ionosphere measurement. The EDTP is the most reliable instrument to measure the electron density and temperature of ionosphere. The EDTP sweeps high frequencies which were applied to a probe and measures the resonance frequency of a plasma in the electron density measurement. The plasma of ionosphere is influenced by the magnetic field of the Earth. Therefore, the electron density varies by the relationship between the plane of the probe and the directions of the magnetic field. We generated a plasma in the space plasma chamber and changed the magnetic field of the chamber using a Helmholtz coil. In this study, we investigated the effects that are caused by the electron density in the direction of the magnetic field. As a result, we found the electron density become very high when the magnetic field was applied to the direction of the front of the disk probe.

Using a Langmuir probe mounted on a large satellite is a general method to directly measure ionosphere’s plasma characteristics, such as electron temperature and electron density. Microsatellites are also being planned to be used for this task due to their apparent advantages, such as low-cost and short development time. However, the deployment of Langmuir probe on a microsatellite faces with a problem that the satellite’s electric potential fluctuates significantly as the plasma’s currents are fed to a satellite’s conducting surface which is not much larger than that of the probe. This in turn adversely affects the accuracy of the observation results. In this paper, a technique exploiting an electron gun is proposed to stabilize this fluctuation. The technique is tested in a space chamber and the obtained results are shown to demonstrate the effective controlling of the satellite electric potential.

To investigate whether the link between seismic activity and EIA (equatorial ionization anomaly) enhancement is valid for mid-latitude seismic activity, DEMETER observations around seven large earthquakes in the north-east Asian region were fully analyzed ( M ⩾ 6.8 ). In addition, statistical analysis was performed for 35 large earthquakes ( M ⩾ 6.0 ) that occurred during the DEMETER observation period. The results suggest that mid-latitude earthquakes do contribute to EIA enhancement, represented as normalized equatorial N e , and that ionospheric change precedes seismic events, as has been reported in previous studies. According to statistical studies, the normalized equatorial density enhancement is sensitive and proportional to both the magnitude and the hypocenter depth of an earthquake. The mechanisms that can explain the contribution of mid-latitude seismic activity to EIA variation are briefly discussed based on current explanations of the geochemical and ionospheric processes involved in lithosphere–ionosphere interaction.

Electron temperature in the sporadic E layer was measured with a glass-sealed Langmuir probe at a mid-latitude station in Japan in the framework of the SEEK (Sporadic E Experiment over Kyushu)-2 campaign which was conducted in August 2002. Important findings are two fold: (1) electron temperature and electron density vary in the opposite sense in the height range of 100–108 km, and electron temperature in the Es layer is lower than that of ambient plasma, (2) electron temperature in these height ranges is higher than the possible range of neutral temperature. These findings strongly suggest that the heat source that elevates electron temperature much higher than possible neutral temperature exists at around 100 km, and/or that the physical parameter values, which are used in the present theory to calculate electron temperature, are not proper.

It has been well known that the ionospheric electron density Ne is greater in the summer nighttime than daytime around the Weddell Sea region, which is named Weddell Sea Anomaly (WSA). This paper for the first time reports unusual increases (decreases) of the daytime (nighttime) electron temperature Te at about 830 km altitude over the WSA latitudes probed by Tatiana-2 during December 2009 to January 2010. Concurrent measurements at 660–830 km altitude observed by Tatiana-2, Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER), and Formosa Satellite 3/Constellation Observing System for Meteorology, Ionosphere and Climate (F3/C) reveal the anticorrelation between Te and Ne along the WSA latitudes in the daytime and nighttime. Based on F3/C Ne along the WSA latitudes observed at various local times, the associated Te values are computed. The Tatiana-2 and DEMETER observations as well as the computed results show that Te yield the maximum values over the WSA region during daytime and over the Indian and Atlantic Ocean area during nighttime. The maxima or minima in F3/C Ne and the computed Te reveal eastward phase shifts.

[1] The existence of hydrated cluster ions is known through in situ measurements in the D region of the ionosphere and laboratory simulation experiments. A series of experiments were conducted at Sagamihara, Japan with the intention of detecting some of the ions which, although predicted, had eluded detection in laboratory simulation. The other motivation was to look for heavier ions in laboratory simulations in conditions close to those in the D region. With the availability of better ion mass spectrometers, these could supposedly be detected by rocket measurements. Results of these experiments point to a new aspect, namely, the production of a neutral hydrated cluster molecule, which (a) has ionization potential of less than 10.2 eV, (b) has lifetimes in excess of 90 min, and (c) is formed within a limited pressure range. As this neutral cluster molecule has a mass number of 102, most probably it is NO⋅(H2O)4. A number of other important ions, which were detected earlier in laboratory experiments, were also seen in our data. These include NO+(H2O)n, NO+(H2O)nX, NO2+(H2O)n, H3O+(H2O)n, H3O+(H2O)nX, and O2+(H2O)n series. A few clusters {36+(H3O+OH), 60+(NO+NO) and 63+(NO+HO2)} and molecular ions {29+(N2H+), 33+(HO2+) and 43+(N3H+)} were also detected in these experiments. It was also found that, like the earlier experiments, the concentration of most of the hydrated ions showed an oscillatory behavior. The ion formation was observed only within a limited pressure range, which corresponds to the 50 to 100 km altitude range of the ionosphere.

In this paper, we examine pre-earthquake ionospheric anomalies by the total electron content (TEC) derived from a ground-based receiver of the global positioning system (GPS). A network of eight GPS receivers is used to construct daily latitude-time-TEC (LTT) plots to monitor the crest of equatorial ionization anomaly (EIA) in the Taiwan area. Three parameters of the strength, location, and formation time of the EIA crest are extracted. A 15-day running medians of the three parameters and the associated upper and lower quartiles are utilized as the references for identifying abnormal signals for all of the 150 M ≧ 5.0 earthquakes in the Taiwan area during 2001–2007. Results show that the EIA crest significantly moves equatorward (poleward) and appears in an earlier (later) time of the afternoon period a few days before (after) the earthquakes along the Taiwan longitude. The two parameters of the EIA crest location and occurrence time can be employed to detect ionospheric earthquake precursors. The results further imply that atmospheric electric fields generated around the epicenter of a forthcoming earthquake during the preparation period are essential.

著者人数: 29名, Accepted: 2010-03-15, 資料番号: SA1002803000

The seismo-ionospheric precursor prior to the Mw7.9 earthquake near Wenchuan, China, on 12 May 2008 was observed by the FORMOSAT-3/COSMIC satellite constellation. By binning radio occultation observations, the three-dimensional ionospheric structure can be obtained to monitor the ionospheric electron density variation prior to the earthquake. It has been determined that near the epicenter the F2-peak height, hmF2, descends about 25 km and the F2-peak electron density, NmF2, decreases about 2 × 105 el/cm3 around noon within 5 days prior to the earthquake. The integrated electron content decreases more than 2 TECU between 250 and 300 km altitude.

Six microsatellites termed Formosa Satellite 3 and Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC or F3/C in short) are employed to study the 3-D structure of the ionospheric electron density during two M7.0 offshore earthquakes occurred near Pingtung, the most south county of Taiwan, on December 26, 2006. Results show that around the epicenters the F2-peak height descends and the ionospheric electron density between 300 and 350 km altitude significantly decreases within 5 days prior to the earthquakes.

The electron temperature (Te), electron density (Ne), and two components of the electric field were measured from the height of 90 km to 150 km by one of the sounding rockets launched during the SEEK-2 campaign. The rocket went through sporadic E layer (Es) at the height of 102 km–109 km during ascent and 99 km–108 km during decent, respectively. The energy density of thermal electrons calculated from Ne and Te shows the broad maximum in the height range of 100–110 km, and it decreases towards the lower and higher altitudes, which implies that a heat source exists in the height region of 100 km–110 km. A 3-D picture of Es, that was drawn by using Te, Ne, and the electric field data, corresponded to the computer simulation; the main structure of Es is projected to a higher altitude along the magnetic line of force, thus producing irregular structures of Te, Ne and electric field in higher altitude.

The Ionosphere and Upper Atmosphere of Venus: A Review

The production rate, ion density and electron density are calculated between longitudes 0° and 360° E due to incident radiation of wavelength range 1-102.57 nm in the dayside atmosphere of Mars. These calculations are made by using global analytical yield spectrum (AYS) model at solar zenith angle 80° between latitudes 50° and 70° N for spring equinox and medium solar activity condition. These conditions are appropriate for Mars Global Surveyor (MGS) Phase 2 aerobraking period during which both the accelerometer and the radio occultation data are used. The calculated results are compared with MGS radio occultation measurements carried out at different latitudes (64.7°-67.3° N) and longitudes (0°-360° E) in December 1998 between solar zenith angle 78° and 81°. This measurement shows primary and secondary ionization peaks, which are varying with longitudes. Our calculation suggests that first peak is produced by photoionization and photoelectron impact ionization processes due to absorption of solar EUV radiation (9-102.57 nm). The second peak is produced by photoelectron impact ionization of soft X-ray photon (1-9 nm). There is a good agreement between our calculation and measurement as far as the maximum and the minimum values of primary peak altitude/peak density of electrons are concerned. However, the calculated values of secondary peak density and peak altitude are higher than the measured values by a factor of 1.5-2.0 and 1.1, respectively. The secondary peak is brought into agreement with the measurement using low X-ray flux by a factor of 2 to 3 below 9 nm. The longitudinal distribution of calculated and measured peak density and peak altitude are fitted by least-square method with 0.95 confidence limits.

El microsatélite Francés-Brasileño (FBM) está programado para lanzarse en el año 2004. Será colocado en una inclinación baja (cercana a 6 grados) en una órbita circular ecuatorial a una altura de 700 km. Entre varios experimentos, llevará un Paquete de Diagnóstico de Plasma (PDP) consistente de 3 experimentos, una Prueba de Capacitancia de Alta Frecuencia (HFC) para medir la densidad absoluta electrónica a lo largo de la trayectoria del satélite, una Prueba de Langmuir (LP) para medir la variación relativa y la distribución espectral de la densidad electrónica y una Prueba de Temperatura Electrónica (ETP) para medir la variación en la temperatura electrónica y el potencial espacial. El principal objetivo del experimento PDP es realizar observaciones globales de las principales características de las burbujas de plasma de bajas latitudes, y por tanto estudiar la dinámica y electrodinámica que controla la generación, desarrollo y decaimiento de estas burbujas. Estas observaciones satelitales se complementarán con observaciones provenientes de una red de equipos tales como ionosondas, digisondas, polarímetros y radares VHF operados simultáneamente por un grupo selecto de estaciones de tierra en Brasil y otros países colaboradores. La operación de los experimentos brasileños a bordo del FBM se controlarán por una computadora especial. Esta computadora estará asociada con la computadora principal que controla la operación del satélite. Los datos del experimento LP se pueden procesar también a bordo para reducir los requerimientos de memoria.

Accepted: 2003-06-20, 資料番号: SA1001684000

Recent spectral measurements of sprites and elves using imaging spectrometers have been limited to the red end of the spectrum (above ), while spectral information from the blue end of the spectrum has been measured only by bandpass-filtered photometers. Although the blue photometric data identified N2 second positive and N2+ first negative band emissions, uncertainty remains in some measurements due to the small separation in the emission lines. Spectrally resolved measurements of the blue components, particularly the emissions of N2+ 1N band, are very important because they indicate the existence of relatively high electron energies and high level of ionization at that altitude and therefore can be a great help in uncovering the generation mechanism for sprites. We have recently developed an intensified CCD slit spectrograph system with a peak sensitivity around with a highly linear dispersion and a spectral resolution of .

The SELENE Project of Japan includes three spacecraft: a main orbiting satellite and two subsatellites. Among many scientific objectives of the Project is the exploration of plasma formations above the lunar surface. The thin plasma layer above the area of the Moon, presented to the Sun, was first detected in radio occultation experiments conducted during 1972 with the Soviet lunar satellite “Luna-19”. The SELENE Project radio science experiment will be realized by means of a dual S- and X- band transmitter installed onboard the orbiter and Earth based antennas. The effect of the thin plasma layer near the Luna can be hidden by the fluctuations of the total electron content of the Earth's ionosphere. Dual spacecraft occultation configurations can remove partially the influence of the Earth's ionosphere. Several dual spacecraft configurations are discussed and upper error limits of total electron content measurements are estimated.

The total photoelectron and secondary electron fluxes are calculated at different times and altitudes along the trajectory of Mars Global Surveyor passing through the nightside and dayside martian ionosphere. These results are compared with the electron reflectometer experiment on board Mars Global Surveyor. The calculated electron spectra are in good agreement with this measurement. However, the combined fluxes of proton and hydrogen atom as calculated by E. Kallio and P. Janhunen (2001, J. Geophys. Res.106, 5617–5634) were found to be 1–2 orders of magnitude smaller than the measured spectra. We have also calculated ionization rates and ion and electron densities due to solar EUV, X-ray, and electron–proton–hydrogen atom impacting with atmospheric gases of Mars at solar zenith angles of 75°, 105°, and 127°. In the vicinity of the dayside ionization peak, it is found that the ion production rate caused by the precipitation of proton–hydrogen atom is larger than the X-ray impact ionization rate while at all altitudes, the photoionization rate is always greater than either of the two. Moreover, X-rays contribute greatly to the photoelectron impact ionization rate as compared to the photoion production rate. The calculated electron densities are compared with radio occultation measurements made by Mars Global Surveyor, Viking 1, and Mars 5 spacecraft at these solar zenith angles. The dayside ionosphere produced by proton–hydrogen atom is smaller by an order of magnitude than that produced by solar EUV radiation. X-rays play a significant role in the dayside ionosphere of Mars at the altitude range 100–120 km. Solar wind electrons and protons provide a substantial source for the nightside ionosphere. These calculations are carried out for a solar minimum period using solar wind electron flux, photon flux, neutral densities, and temperatures under nearly the same areophysical conditions as the measurements.

We study the behavior of the F region ionosphere in the Northern Hemisphere during the sudden stratospheric warming period of 19–30 January 2009 by using FORMOSAT-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) ionosphere data (NmF2, hmF2, and height profile). We concentrated our study in the longitude bands 30°E–30°W, as well as 150°E–150°W, where no detailed study has been reported so far. At low magnetic latitude, the NmF2 decreases except during 09–12 LT: in the latitude zone of 20–40° NmF2 shows an increase of 30% during 09–12 LT. At higher magnetic latitude the NmF2 shows an increase during daytime and a reduction in the evening (21–03 LT). There is a latitude zone where NmF2 does not change. The latitude seems to correspond to the latitude where atmospheric temperature does not change. The behavior of the NmF2 seems to suggest a reduction of neutral density in low latitude and increase of neutral density in higher latitude. During the period of day of year (DOY) 25–31, the NmF2 shows a drastic reduction only during 06–09 LT in low latitudes, which is slightly away from geomagnetic equator. This special feature which occurred during declining phase of the sudden stratospheric warming (SSW) might be explained as due to enhanced dynamo electric field. The study suggests global change of the thermosphere including dynamo region, in spite of the fact that SSW is a high-latitude phenomenon which occurred much below the height region of thermosphere.

International audience; Anomalous changes in the ionospheric conditions related to the Wenchuan earthquake of 12 May 2008 are investigated using electron density (Ne) from Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and CHAMP satellites, electric field from DEMETER, and GPS-total electron content (TEC) maps. The normalized Ne from the DEMETER satellite reveal that the previously reported TEC increments before the earthquake can be considered as fragments of the gradual equatorial ionization anomaly (EIA) enhancements near the epicenter longitude that began approximately 1 month before the earthquake and reached its maximum with an exceptionally large strength index 8 days prior to the main shock. This feature is indirectly confirmed through the CHAMP Ne and GPS TEC data. Following the EIA intensity peak, disturbances in the Ne and O+ density were observed in the nightside. Based on the concurrent electric field and Ne changes, it is suggested that EIA intensification could be triggered by the E field disturbances over the epicenter.

A feasibility study to observe the low-density Martian nightside ionosphere and the cislunar electron layer by radio occultation technique is presented. Since the total electron contents (TECs) along the ray paths of radio occultation in the ionospheres of Mars and the Moon are comparable to the fluctuation of the TEC of the terrestrial ionosphere, the distortions of radio occultation data by the terrestrial ionosphere should be taken into account. Local time and seasonal dependences of the terrestrial TEC fluctuations are investigated using the GPS receiver network, showing that the terrestrial ionosphere is calm at night in winter and that this period is suitable for the radio occultation measurements of the planetary ionospheres. A method is also developed to estimate the terrestrial TEC fluctuation along the ray path of radio occultation from GPS TEC data.

The aeronomy experiments on the Pioneer Venus Orbiter (PVO) have established three characteristic features of the nightside ionosphere of Venus: (1) disappearing ionospheres, (2) large spatial/temporal variability of ion densities and (3) plasma holes/troughs. As the nightside ionosphere is essentially maintained by the transterminator flow of O+ ions from the dayside, this flow should then be the major parameter controlling these features. Disappearing ionospheres, for example, have indeed been found to occur during episodes of high solar wind dynamic pressure (Psw), when the height of the terminator ionopause is greatly reduced and thus the transterminator flow severely diminished. In this paper, we study the other two features, viz the temporal/spatial ion density variability and the location of plasma holes/troughs by analyzing O+ density profiles measured by the ion mass spectrometer experiment on the PVO. We find that most of the variability in the central nightside ionosphere is related to Psw, which is seen to control the O+ peak density. Further, we observe that the altitude of the plasma holes/troughs is also dependant on Psw.

Accepted: 2000-12-15, 資料番号: SA1001673000