Search

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.

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.

As one of the tasks to find the energy source(s) of thermal electrons, which elevate(s) electron temperature higher than neutral temperature in the lower ionosphere E-region, energy distribution function of thermal electron was measured with a sounding rocket at the heights of 93–131 km by the applying second harmonic method. The energy distribution function showed a clear hump at the energy of ~0.4 eV. In order to find the reason of the hump, we conducted laboratory experiment. We studied difference of the energy distribution functions of electrons in thermal energy range, which were measured with and without EUV radiation to plasma of N2/Ar and N2/O2 gas mixture respectively. For N2/Ar gas mixture plasma, the hump is not clearly identified in the energy distribution of thermal electrons. On the other hand for N2/O2 gas mixture, which contains vibrationally excited N2, a clear hump is found when irradiated by EUV. The laboratory experiment seems to suggest that the hump is produced as a result of interaction between vibrationally excited N2 and thermal electrons, and this interaction is the most probable heating source for the electrons of thermal energy range in the lower E-region. It is also suggested that energy distribution of the electrons in high energy part may not be Maxwellian, and DC probe measures the electrons which are non Maxwellian, and therefore "electron temperature" is calculated higher.

Empirical models of Total Electron Content (TEC) based on functional fitting over Taiwan (120° E, 24° N) have been constructed using data of the Global Positioning System (GPS) from 1998 to 2007 during geomagnetically quiet condition (Dst>−30 nT). The models provide TEC as functions of local time (LT), day of year (DOY) and the solar activity (F), which are represented by 1–162 days mean of F10.7 and EUV. Other models based on median values have been also constructed and compared with the models based on the functional fitting. Under same values of F parameter, the models based on the functional fitting show better accuracy than those based on the median values in all cases. The functional fitting model using daily EUV is the most accurate with 9.2 TECu of root mean square error (RMS) than the 15-days running median with 10.4 TECu RMS and the model of International Reference Ionosphere 2007 (IRI2007) with 14.7 TECu RMS. IRI2007 overestimates TEC when the solar activity is low, and underestimates TEC when the solar activity is high. Though average of 81 days centered running mean of F10.7 and daily F10.7 is often used as indicator of EUV, our result suggests that average of F10.7 mean from 1 to 54 day prior and current day is better than the average of 81 days centered running mean for reproduction of TEC. This paper is for the first time comparing the median based model with the functional fitting model. Results indicate the functional fitting model yielding a better performance than the median based one. Meanwhile we find that the EUV radiation is essential to derive an optimal TEC.

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.

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 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

Accepted: 2000-05-16, 資料番号: SA1001701000

Observations made by the Hinotori satellite have been analysed to determine the yearly variations of the electron density and electron temperature in the low-latitude topside ionosphere. The observations reveal the existence of an equinoctial asymmetry in the topside electron density at low latitudes, i.e. the density is higher at one equinox than at the other. The asymmetry is hemisphere-dependent with the higher electron density occurring at the March equinox in the Northern Hemisphere and at the September equinox in the Southern Hemisphere. The asymmetry becomes stronger with increasing latitude in both hemispheres. The behaviour of the asymmetry has no significant longitudinal and magnetic activity variations. A mechanism for the equinoctial asymmetry has been investigated using CTIP (coupled thermosphere ionosphere plasmasphere model). The model results reproduce the observed equinoctial asymmetry and suggest that the asymmetry is caused by the north-south imbalance of the thermosphere and ionosphere at the equinoxes due to the slow response of the thermosphere arising from the effects of the global thermospheric circulation. The observations also show that the relationship between the electron density and electron temperature is different for daytime and nighttime. During daytime the yearly variation of the electron temperature has negative correlation with the electron density, except at magnetic latitudes lower than 10°. At night, the correlation is positive.Key words: Ionosphere (equatorial ionosphere; ionosphere-atmosphere interactions; plasma temperature and density)

Irregularities in electron density related to a nighttime sporadic-E (Es) layer were measured by a fixed-bias Langmuir probe onboard the sounding rocket S-310-25, launched at 23:00:00 JST on August 26, 1996 during the SEEK observation campaign. The most interesting finding was the existence of multiple-Es layers which were separated by 10 – 12 km within a wide altitude range of 90 – 130 km. Meter-scale irregularities generated in association with the multiple-Es layers were found to exist in a similar altitude range as quasi-periodic (QP) echoes, which were detected with frequency agile radar (FAR) operating at 24.5 MHz around the time of the rocket flight.

Rocket measurements of electron temperatures (Te) in the E region over Kagoshima Space Center, Japan, carried out in a serees of experiments conducted from 1970 to 1988 are analysed in this paper. All the 13 flights whose results are presented here took place around 11 AM, close to the Sq current intensity maximum. Anomalously high electron temperatures associated with large increases of high energy tail electron population were observed whenever the estimated Sq current vortex was very close to the launch site. Such anomalous temperatures were observed only in local winter months. A mechanism for the anomalous heating is proposed based on the solsticial asymmetry of the Sq electric potentials and the resulting field-aligned current that could flow from winter to summer hemisphere.

Accepted: 1999-06-09, 資料番号: SA1001672000

Electron temperatures up to 8000km were observed by the Japanese scientific satellite “AKEBONO” which was launched in 1989 with an inclination of 75 degrees. Since launch, satellite data have been recorded at four tracking stations; Kagoshima in Japan, Esrange in Sweden, Prince Albert in Canada, and Showa in Antarctica. The observations cover latitudes up to 75 degrees, for all longitudes and local times. The paper mainly describes features of the height profiles of electron temperature, with regards to variations in local time, latitude and season. The intent is to contribute to the construction of a model of electron temperature at altitudes over 1000 km.

[1] This paper reports the existence of plasma caves, minima in the electron density located at 5–10° to the magnetic equator, in the bottomside ionosphere based on electron densities simulations from the International Reference Ionosphere (IRI-2007) and clear evidences given by plasma density and drift measurements of the Dynamic Explorer 2 (DE 2) satellite during 1981–1983. The IRI simulations suggest plasma caves as daytime features (08:00–19:00 LT; length of 18,158 km in the longitudinal direction), that range from theE region up to about 300 km altitude with 10° (or 1100 km) width in the latitudinal direction. In situ measurements of the ion and electron densities probed by the DE 2 confirm the existence of the plasma caves at low altitudes of the EIA ionosphere. The unexpected downward and upward (or weakly and strongly upward) ion drifts at the magnetic equator and the two off equators seem to play an important role responsible for the plasma cave formation.

[1] During the SELENE (Kaguya) mission the dual-spacecraft radio occultation technique was used to investigate the electron population in the vicinity of the lunar surface. One pair of coherent S-band radio signals from one spacecraft was used to probe the possible electron density enhancement near the Moon, and another signal pair from the other spacecraft measured the solar wind and the terrestrial ionosphere plasma fluctuations, which also exist in the measurement by the former signal pair. The results suggest that any stable ionosphere with densities comparable to the ones observed by the Soviet Luna 19 and 22 missions does not exist near the terminator at high latitudes, although the occurrence of temporal or localized density enhancements cannot be ruled out.

The electron density distribution in the vicinity of the lunar surface was explored with the radio occultation technique using a subsatellite on the SELENE mission. Although the measurements suffer from contamination by the terrestrial ionosphere and interplanetary plasma, an analysis of more than 300 measurements provides adequate statistics and reveals a general trend. The result suggests that a dense ionosphere covering the whole sunlit side, as suggested by the radio occultation measurements on the Soviet Luna 19 and 22 missions, does not exist. However, weak signatures of electron density enhancement with densities on the order of 100 cm(-3) are observed below 30 km altitude at solar zenith angles less than 60 degrees. The statistically averaged density reaches a peak at around 15 km altitude and decreases gradually at higher altitudes and toward the surface. Although the suggested electron layer is thinner and less extended horizontally than that reported by Luna 19 and 22, the existence of such an ionized layer is still difficult to explain by conventional ionosphere generation mechanisms. An alternative source of electrons may be required.

Electron temperature data obtained aboard two satellites are compared with the IRI model. Our comparison may serve as an input to a future version of IRI. HINOTORI data show IRI90 to predict night time T e quite well with the exception of a few peculiar phenomena, in particular a morning overshoot at height around 600 km and anomalous T e observations of AKEBONO for the first time allowed to extend reliably the temperature profile up to − 8000km. This profile clearly depends on local time at all invariant latitudes. The data suggest strong influence of solar activity on electron temperature.

[1] Data obtained by the U.S. satellite DE‐2 are used to investigate possible precursor features in the ionosphere associated with a large earthquake (latitude �33.13°, longitude 73.07°, M = 7.5), which occurred during a moderate geomagnetic disturbance. Atomic oxygen ion and molecular ion distributions show characteristic latitudinal features similar to the well‐known equatorial ionization anomaly (EIA) feature but centered around the earthquake epicenter. We name this the precursor ionization anomaly (PIA). The density minima of both the atomic oxygen and molecular ions are in two latitude zones, depending on the distance from the epicenter. One of the PIA minima aligns with the geomagnetic latitude crossing the epicenter. Another minimum is found along the geographic latitude of the epicenter. These minima are located in an area spanning about 40° in latitude and about 140° in longitude. It is noted that the molecular ion minimum is more clearly defined even when the atomic ion density minimum is not indicated clearly. The ion density reduction seems to be caused by a superposition of natural/quiet time ionospheric eastward electric field and an electric field associated with the earthquake. Although we studied one single event, our careful examination of results suggests that the location and day of occurrence of the PIA can be predicted for some large earthquakes even during moderate geomagnetic disturbance if the satellite orbit is properly chosen.

[1] This paper derives the theoretical relationship between vertical integrated intensity of OI 135.6 nm oxygen emission with integrated electron content (IEC) from 150 to 800 km altitude as well as F layer peak electron density (NmF2). Local time, seasonal, and solar cycle dependence of the relationship is investigated, and it is proposed as a conversion factor to retrieve IEC and NmF2 values from airglow measurements. The errors associated with the IEC and NmF2 estimation using the derived conversion factor are demonstrated for different local times and solar activity. The theoretical conversion factor is compared with that calculated using airglow measurements by the Global Ultraviolet Imager onboard the Theremosphere, Ionosphere, Mesosphere Energetics and Dynamics mission and the Global Ionospheric Map total electron content as well as the nadir integrated OI 135.6 nm intensity by the Tiny Ionospheric Photometer and NmF2 determined from the Global Positioning System Occultation Experiment, both onboard FORMOSAT-3/COSMIC.

Electron density and temperature profiles in the mid latitude ionosphere are derived from the ”resonance cone” in the radiation pattern of high-frequency point antennas aboard a sounding rocket. By comparing the shapes for reversed wave propagation direction it is possible to study electron drift motion and field-aligned beams. The data from the COREX-I (Cooperative Resonance Cone Experiment) experiment show close agreement of electron density and temperature profiles from resonance cones with results from independent instruments. There was no indication of a substantial temperature anomaly at E region altitude during this flight. An unexpected electron drift can be interpreted as electron Hall current in the presheath of the negatively charged payload. Field-aligned beams, which have been suggested in connection with the temperature anomaly, were not detected.

[1] Global distributions of presunrise ion heating were discovered by the Ionospheric Plasma and Electrodynamics Instrument onboard the ROCSAT-1 satellite in the low- to midlatitude topside ionosphere. The most significant presunrise ion heating was clearly found in the 0400–0500 LT sector and asymmetrically located in the South Pacific and North Atlantic region during the June and December soltices, respectively. Local time variations of ion temperature from 0000 to 0600 LT indicate that the temperature of the presunrise heating increases gradually after its early onset. Despite the late onset of the sunrise heating, the temperature increases rapidly and goes beyond that of the presunrise heating after 0430 LT. To identify possible heating sources, electron temperature observed by the HINOTORI satellite is compared and found similar patterns to the distributions of the presunrise ion heating. With the aid of the SAMI2 model of the ionosphere, these distributions and the local time variations of the temperature at 600 km altitude can be reproduced. The presunrise plasma heating is caused by photoelectrons streaming along field lines from low altitudes of the sunlit magnetic conjugate ionosphere. The early onset of the presunrise heating is one of the main factors to maintain the plasma temperature higher before 0430 LT. In addition, abundant amounts of light ions act as proxies in the processes of the presunrise heating to indirectly transfer thermal energy from electrons to O+ and to speed up the increase of O+ temperature. Asymmetrical hemispheric temperature distributions of the presunrise heating during the solstices are the result mainly of the geomagnetic dipole offset from the center of the Earth.

The data from the COREX instrument are discussed with respect to non-reciprocities in resonance cones for opposing wave propagation directions. The shift of the maxima has a different symmetry from the case of field aligned drifts. Using a generalized drift model the magnitude and direction of the drift is evaluated. Velocities of the order of up to 38 km/s are found. The drift direction is nearly perpendicular to the magnetic field.

[1] A coordinated observation of the atmospheric response to auroral energy input in the polar lower thermosphere was conducted during the Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign. N2 rotational temperature was measured with a rocket-borne instrument launched from the Andoya Rocket Range, neutral winds were measured from auroral emissions at 557.7 nm with a Fabry-Perot Interferometer (FPI) at Skibotn and the KEOPS, and ionospheric parameters were measured with the European Incoherent Scatter (EISCAT) UHF radar at Tromso. Altitude profiles of the passive energy deposition rate and the particle heating rate were estimated using data taken with the EISCAT radar. The local temperature enhancement derived from the difference between the observed N2 rotational temperature and the MSISE-90 model neutral temperature were 70–140 K at 110–140 km altitude. The temperature increase rate derived from the estimated heating rates, however, cannot account for the temperature enhancement below 120 km, even considering the contribution of the neutral density to the estimated heating rate. The observed upward winds up to 40 m s �1 seem to respond nearly instantaneously to changes in the heating rates. Although the wind speeds cannot be explained by the estimated heating rate and the thermal expansion hypothesis, the present study suggests that the generation mechanism of the large vertical winds must be responsible for the fast response of the vertical wind to the heating event.

Accepted: 2009-08-06, 資料番号: SA1000825000

[1] The global ionospheric map (GIM) is used to observe variations in the total electron content (TEC) of the global positioning system (GPS) associated with 35 M ≥ 6.0 earthquakes that occurred in China during the 10-year period of 1 May 1998 to 30 April 2008. The statistical result indicates that the GPS TEC above the epicenter often pronouncedly decreases on day 3–5 before 17 M ≥ 6.3 earthquakes. The GPS TEC of the GIM and electron density profiles probed by six microsatellites of FORMOSAT3/COSMIC (F3/C) are further employed to simultaneously observe seismoionospheric anomalies during an Mw7.9 earthquake near Wenchuan, China, on 12 May 2008. It is found that GPS TEC above the forthcoming epicenter anomalously decreases in the afternoon period of day 6–4 and in the late evening period of day 3 before the earthquake, but enhances in the afternoon of day 3 before the earthquake. The spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions, respectively. The F3/C results further show that the ionospheric F2 peak electron density, NmF2, and height, hmF2, significantly decreases approximately 40% and descends about 50–80 km, respectively, when the GPS TEC anomalously reduces.

Electron temperature probes have been installed in five Japanese scientific satellites, starting with satellite TAIYO which was launched in 1975 to satellite AKEBONO launched in 1989. We describe here our unique electron temperature probes which were installed in these Japanese satellites and briefly overview the mission objectives and misson lives of these satellites. Several geophysical contributions made by these satellites are summarized. Typical examples of the results are presented such as anisotropy of electron temperature, temperature structure inside plasma bubbles and electron temperature around field aligned currents in the polar region. Finally we will discuss our possible contribution to IRI model.

[1] We examine ionospheric electron temperatures (Te) observed by HINOTORI satellite during three earthquakes; M6.6 occurred in November 1981, M7.4 and M6.6 in January 1982 over Philippine, respectively. It is found that T e around the epicenters significantly decreases in the afternoon periods within 5 days before and after the three earthquakes. The region of ionosphere disturbance extends to 80-120 degrees in longitude. A tendency exists that duration of the disturbance becomes longer as the increase of earthquake magnitude. F 2 peak frequency, f o F 2 and virtual height, h'F from a chain of 4 ionosonde stations located in the longitude zone of 120°E-130°E are used together with electron density(N e ), that is observed simultaneously onboard HINOTORI satellite to find possible cause mechanisms of the abnormal reduction of electron temperatures. Behavior of HINOTORI T e /N e and ionosonde f o F 2 /h'F implies the existence of westward electric field over epicentre. Our finding suggests that simple two plasma instruments might be able to play a fundamental role to study ionosphere disturbance associated with earthquake, if the constellation of small/mini satellites is organized and the orbits are properly chosen.

[1] We investigated meridional and seasonal variations in small-vertical-scale (wavelengths 0.5–3 km) fluctuations of the ozone mixing ratio in the lower stratosphere using ozonesonde data covering wide longitudinal and latitudinal regions in all seasons. The generation of mixing ratio fluctuation is attributed to vertical advection and/or horizontal advection; the former was estimated from the potential temperature fluctuation and the vertical gradient of background mixing ratio, while the latter was obtained by subtracting the vertical advection component from the observed value. The results show that horizontal advection is always the major source of the mixing ratio fluctuation above the potential temperature of 700 K (∼27 km altitude). Below 700 K, the source of the mixing ratio fluctuation depends on latitude; horizontal advection governs the mixing ratio fluctuations at high latitudes, vertical advection dominates at low latitudes, and horizontal advection is relatively dominant in winter–spring, while vertical advection is dominant in summer–autumn in the midlatitudes. These tendencies were confirmed by analyzing the correlation between the small-scale structures of the mixing ratio and the potential temperature. The synthetic distribution of the horizontal advection activity due to synoptic-scale motions calculated from assimilated meteorological data reproduced the seasonal, meridional, and altitudinal tendencies of the observed small-scale fluctuations, suggesting the major contribution of differential advection via large-scale winds.

Accepted: 2005-01-10, 資料番号: SA1001702000

[i] The detailed model calculations of photoelectron flux and nightglow emissions of 5577 and 6300 A lines are made using analytical yield spectrum approach based on Monte Carlo method. The calculated photoelectron spectra are compared with electron reflectometer (ER) measurements made by Mars Global Surveyor (MGS) at the energy range 10-1000 eV. This calculation suggests that X-ray ionization is an important process in the dayside ionosphere of Mars at energy greater than 90 eV, and 10- to 90-eV electron population is controlled by photoionization and photoelectron impact ionization. The secondary electron flux, excitation rates, emission rates, and limb intensities of 5577 and 6300 A lines are calculated due to precipitation of solar wind electrons observed by ER experiment at the energy range 10-1000 eV in the nighttime ionosphere of Mars. In the vicinity of the peak altitudes, it is found that excitation/emission of atomic oxygen after the electron impact dissociation of CO 2 is the main source of 5577 A emissions, while dissociative recombination of molecular oxygen ion is the major source of 6300 A emissions after the electron impact excitation of atomic oxygen. The calculated secondary electron spectra are also compared with ER experiment measurements between energies of 10 and 1000 eV. The nightglow limb intensities are compared with the upper limit set by Mars 5 spectroscopic observations.

We present a comparison of the observed behavior of the F region ionosphere over Millstone Hill during the geomagnetically quiet and storm period on 16-23 March, 1990, with numerical model calculations from the time-dependent mathematical model of the Earth's ionosphere and plasmasphere. The effects of vibrationally excited N2(v) and O2(v) on the electron density and temperature are studied using the N2(v) and O2(v) Boltzmann and non-Boltzmann distribution assumptions. The deviations from the Boltzmann distribution for the first five vibrational levels of N2(v) and O2(v) were calculated. The present study suggests that these deviations are not significant at vibrational levels v = 1 and 2, and the calculated distributions of N2(v) and O2(v) are highly non-Boltzmann at vibrational levels v > 2. The N2(v) and O2(v) non-Boltzmann distribution assumption leads to the decrease of the calculated daytime NmF2 up to a factor of 1.44 (maximum value) in comparison with the N2(v) and O2(v) Boltzmann distribution assumption. The resulting effects of N2(v > 0) and O2(v > 0) on the NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 2.8 (maximum value) for Boltzmann populations of N2(v) and O2(v) and up to a factor of 3.5 (maximum value) for non-Boltzmann populations of N2(v) and O2(v) . This decrease in electron density results in the increase of the calculated daytime electron temperature up to about 1040-1410 K (maximum value) at the F2 peak altitude giving closer agreement between the measured and modeled electron temperatures. Both the daytime and nighttime densities are not reproduced by the model without N2(v > 0) and O2(v > 0) , and inclusion of vibrationally excited N2 and O2 brings the model and data into better agreement. The effects of vibrationally excited O2 and N2 on the electron density and temperature are most pronounced during daytime.Key words: Ionosphere (ion chemistry and composition; ionosphere-atmosphere interactions; ionospheric disturbances)

Results from the resonance cone experiment COREX are reported. Besides electron density and - temperature measurements, the instrument is intended for measuring non-Maxwellian features of the distribution function. The temperature anomaly at the height of 90–120km is discussed.

A tethered payload experiment (Charge-2) was carried out as an international program between Japan and the USA using a NASA sounding rocket at White Sands Missile Range. The objective of the experiment was to perform a new type of active experiment in space by injecting an electron beam from a mother-daughter rocket system connected with a long tether wire. The electron beam with voltage and current up to 1 kV and 80 mA (nominal) was injected from the mother payload. An insulated conductive wire of 426 m length connected the two payloads, the longest tether system flown so far. The electron gun system and diagnostic instruments (plasma, optical, particle and wave) functioned correctly throughout the flight. The potential rise of the mother payload during the electron beam emission was measured with respect to the daughter payload. The beam trajectory was detected by a camera onboard the mother rocket. Wave generation and current induction in the wire during the beam emission were also studied.

We make an attempt to quantify directly the latitudinal profile of the solar wind velocity around equatorial low-speed region, based on observations made by Sakigake, Suisei, and IMP 8 between March 1986 and April 1987, without using the assumption that the location of the minimum velocity just coincides with that of the neutral sheet. We use the formula {ital V}(km/s) ={ital A} sin{sup 2} ({phi}{minus}{phi}{sub A})+{ital B}, to parametarize the latitudinal profile. {ital A} and {ital B} are found to be 1500--11,000 km/s and 340--400 km/s, respectively, which means that the angular width of the low-speed region below 500 km/s is about 17{degree}. These values also indicate the latitudinal velocity gradient of 30 km/s/deg at the portion of velocity of 500 km/s; {phi}{sub {ital A}}, the latitude of the minimum velocity, oscillated sinusoidally around the solar equation as a function of longitude. The amplitude of the sinusoidal oscillation was 4{degree}--9{degree} in 1986 and 1{degree}--2{degree} in early 1987. These amplitudes are smaller than the tilt angle of the neutral line calculated from the photospheric magnetic field. {copyright} American Geophysical Union 1989