Properties Of Ionosphere Research Articles

曲靖地区电离层准6日扰动与MLT大气行星波的相关性

MF radar derived wind measurements and ionosonde data taken above Qujing (25.6°N, 103.8°E) from September to November 2008 are used to investigate the relationship between the atmospheric planetary wave in the mesosphere-lower thermosphere (MLT) and the quasi 6 day oscillation in the ionosphere. The results show that there is strong correlation between the quasi 6 day oscillation in the critical frequency of the sporadic E layer (foEs) and that of the zonal wind, which is related to the atmospheric planetary wave. This quasi 6 day atmospheric planetary wave in the MLT indirectly influences the Es layer by modulating the semidiurnal tides. No obvious planetary type oscillations seem to occur in the F region. These results could act as the experimental evidence for the coupling between the atmosphere planetary wave and ionospheric Es layer, which allows understanding of the ionospheric space-weather properties in low latitude regions of China.

Global-scale observations of ionospheric convection during geomagnetic storms

[1] The global effects on the ionosphere during periods of intense geomagnetic activity associated with geomagnetic storms are investigated using the Super Dual Auroral Radar Network (SuperDARN). The influence of the main and recovery phases of geomagnetic storms on ionospheric properties such as backscatter occurrence rates, velocity distributions, and convection patterns are presented. The evolution of magnetosphere and ionosphere parameters during the storms did not depend on the origin of the storm (e.g., a coronal mass ejection or a corotating interaction region). Instead, there was a continuum of response to the intensity of the driver. For example, we found a clear relationship between the most negative value of the southward component of the interplanetary magnetic field (IMF Bz) and the most negative value of the Sym-H index, which marks the end of the main phase of a storm. This is one of the first superposed epoch studies that analyzes the sunward/antisunward line-of-sight velocity as a function of magnetic local time for geomagnetic storms of various intensities. In the noon sector, before and during the main phase of the storms, the SuperDARN radars recorded faster antisunward ionospheric plasma drifts together with a significant increase in the number of ionospheric echoes. This is consistent with the expected increase in soft particle precipitation in the noon sector and with the reconnection electric field that occurs when the IMF Bz is strongly negative, as is the case during the main phase of storms. The SuperDARN echo occurrence in the noon sector returned to prestorm values early in the recovery phase. The overall response was similar in the midnight sector, except that the peak echo occurrence for the most intense storms was limited to a narrower time interval centered on the end of the main phase. There were reductions in the strong antisunward flows near local midnight observed during the main phase and early in the recovery phase, particularly for the intense storm class. Strong electric fields are applied in the nightside ionosphere during storms, and the decameter structures from which SuperDARN scatter are more easily produced. However, in regions of energetic auroral precipitation and after a long exposure to strong electric fields, there is often a reduction in SuperDARN echoes due to absorption or changes in radio wave propagation.

Magnetic states of the ionosphere of Venus observed by Venus Express

Strong ultraviolet radiation from the Sun ionizes the upper atmosphere of Venus, creating a dense ionosphere on the dayside of the planet. In contrast to Earth, the ionosphere of Venus is not protected against the solar wind by a magnetic field. However, the interaction between charged ionospheric particles and the solar wind dynamic and magnetic pressure creates a pseudo-magnetosphere which deflects the solar wind flow around the planet ( Schunk and Nagy, 1980). The combination of changing solar radiation and solar wind intensities leads to a highly variable structure and plasma composition of the ionosphere. The instrumentation of the Venus Express spacecraft allows to measure the magnetic field (MAG experiment) as well as the electron energy spectrum and the ion composition (ASPERA-4 experiment) of the upper ionosphere and ionopause. In contrast to the earlier Pioneer Venus Orbiter (PVO) measurements which were conducted during solar maximum, the solar activity was very low in the period 2006–2009. A comparison with PVO allows for an investigation of ionospheric properties under different solar wind and EUV radiation conditions. Observations of MAG and ASPERA have been analyzed to determine the positions of the photoelectron boundary (PEB) and the “magnetopause” and their dependence on the solar zenith angle (SZA). The PEB was determined using the ELS observations of ionospheric photoelectrons, which can be identified by their specific energy range. It is of particular interest to explore the different magnetic states of the ionosphere, since these influence the local plasma conductivity, currents and probably the escape of electrons and ions. The penetration of magnetic fields into the ionosphere depends on the external conditions as well as on the ionospheric properties. By analyzing a large number of orbits, using a combination of two different methods, we define criteria to distinguish between the so-called magnetized and unmagnetized ionospheric states. Furthermore, we confirm that the average magnetic field inside the ionosphere shows a linear dependence on the magnetic field in the region directly above the PEB.

Periodic solar wind forcing due to recurrent coronal holes during 1996–2009 and its impact on Earth's geomagnetic and ionospheric properties during the extreme solar minimum

Periodicities in the area of coronal hole (CH) regions on the solar disk and solar wind (SW) high‐speed streams (HSSs) have been studied, for the first time, during complete solar cycle 23 (SC 23) from 1996 to 2009 using solar EUV image data from the Solar and Heliospheric Observatory and STEREO satellites and ACE solar wind‐magnetic data. Both the SW velocity and the area of CH regions consistently exhibit large values during the declining phase and the minimum of SC23 (2003–2009) due to equatorward extended holes and/or low‐latitude isolated holes. Further, the SW velocity and CH area exhibit a greater tendency for subharmonic (13.5 and 9 day) periodicities during the declining phase and solar minimum. The response of Earths' geomagnetic and ionospheric properties to these periodicities associated with corotating interaction regions in SW HSSs is studied, with a focus on the extremely low‐solar‐activity period of 2008. Subharmonic oscillations in both day‐ and nightside ionospheric electron density are found to correlate well with oscillations in SW and Kp during 2008. The topside ionospheric response (above 350 km) appears to be dominated by changes in the plasma temperature and/or scale height and exhibits concurrent enhancements with the oscillations in geomagnetic activity during both day‐ and nighttime. However, the electron density response at altitudes between 200 and 350 km is dominated by changes in the neutral composition and exhibits significant latitudinal, local time, and seasonal variations. The results are discussed in light of equatorward wind perturbations during enhanced geomagnetic activity and summer‐to‐winter transequatorial neutral wind patterns.

Numerical analysis of ionosphere disturbances and Schumann mode splitting in the Earth‐ionosphere cavity

The variability of ionosphere properties plays an important role in the Schumann resonances (SR), amplitudes, frequencies, and Q factor. Therefore, as atmosphere ionization is related to solar activity, SR could be devised as a source of indirect parameters that locally from the surface of the Earth could provide space weather information. A proper understanding of this link to SR parameters can be obtained through finite difference time domain (FDTD) simulations, specifically with the numerically obtained modes and frequencies that relate frequency shifts to the day‐night asymmetry and polar inhomogeneities. Day‐Night asymmetry is observed to have a minor influence in SR; however, large changes are deduced from polar nonuniformities associated to Solar Proton Events (SPE) and X‐ray bursts. The field volume distribution of the modes provides the understanding of the SR variability, related to the altitude and latitude of the ionization phenomenon.

Schumann Resonances as a Means of Investigating the Electromagnetic Environment in the Solar System

The propagation of extremely low frequency (ELF, 3 Hz to 3 kHz) radio waves and resonant phenomena in the spherical Earth-ionosphere cavity has been studied for almost fifty years. When such a cavity is excited by naturally occurring broadband electromagnetic radiation, resonances can develop if the equatorial circumference is approximately equal to an integral number of wavelengths of the propagating electromagnetic waves; these are termed Schumann resonances. They provide information not only about thunderstorm and lightning activity on the Earth, and their relation to climate, but also on the properties of the low ionosphere. Similar investigations can be performed for any other planet or satellite, provided that it has an ionosphere.

On a mechanism forming a broadband maximum in the spectrum of background noise at frequencies 2–6 Hz

We study the properties of a broadband spectral maximum (BSM) of the background noise at frequencies 2–6 Hz using the data of mid-latitude observations. We find that the parameters of the maximum depend on the local ionosphere properties and that small scales (several tens of km) are absent in the field distribution at the BSM frequencies. We propose a mechanism forming the BSM, which is related to the large gradients of the refractive indices of normal ionospheric-plasma waves at altitudes from 70 to 300 km. The performed simulation of BSM spectra for a plane-stratified model of anisotropic inhomogeneous ionosphere allowed us to explain the main experimentally observed BSM properties.

Ionospheric local model and climatology from long‐term databases of multiple incoherent scatter radars

Empirical ionospheric local models have been developed from long‐term data sets of seven incoherent scatter radars spanning invariant latitudes from 25° to 75° in American, European and Asian longitudes at Svalbard, Tromsø, Sondrestrom, Millstone Hill, St. Santin, Arecibo and Shigaraki. These models, as important complements to global models, represent electron density, ion and electron temperatures, and ion drifts in the E and F regions, giving a comprehensive quantitative description of ionospheric properties. A case study of annual ionospheric variations in electron density and ion temperature is presented based on some of these models. Clear latitudinal, longitudinal, and altitude dependency of annual and semiannual components are found.

Non-LTE effects on [formula omitted] emission in the jovian upper atmosphere

Calculations of column intensities are performed for a number of infrared transitions of the H 3 + molecular ion, using a model atmosphere recently produced by Grodent et al. [2001. A self-consistent model of the jovian auroral thermal structure. J. Geophys. Res. 106, 12933–12952]. The line intensities integrated along the line of sight through the model atmosphere are first computed assuming that all of the emitting energy levels are in local thermodynamic equilibrium (LTE). These results are compared with those derived from a detailed balance calculation using a method recently proposed by Oka and Epp [2004. Non-thermal rotational distribution of H 3 + . Astrophys. J. In press]. It is shown that the population of excited vibrational levels starts to depart from that derived from LTE at altitudes higher than 500 km (above the jovian cloud tops). This effect has been noted previously by Kim et al. [1992. Densities and vibrational distribution of H 3 + in the jovian auroral atmosphere. J. Geophys. Res. 97, 6093–6101]. By 2000 km, all of the excited vibrational levels are populated at less than 10% of the expected LTE value. This has important implications for the jovian upper atmosphere. In particular, the H 3 + cooling effect will be greatly reduced high in the atmosphere. Modelled LTE line emission is greater than that derived from non-LTE modelling. Comparison of the non-LTE modelling with recent spectral measurements of the jovian auroral/polar regions in the L- and K-infrared windows shows that the Grodent et al. [2001. A self-consistent model of the jovian auroral thermal structure. J. Geophys. Res. 106, 12933–12952] profile overestimates the measured line intensity by ∼3. Allowing for this, the non-LTE modelling shows that the column densities derived from (quasi-)LTE treatment of the measured line intensities may underestimate the real H 3 + abundance by a factor of between 6 and 200. This means that attempts to derive important ionospheric properties, such as conductivity and related energy inputs due to magnetosphere–ionosphere coupling, from observed spectra will need to take this into account, if they are not to be seriously in error.

Science opportunities with a double Langmuir probe and electric field experiment for JIMO

The three icy Galilean moons of Jupiter: Callisto, Ganymede, and Europa, offer a range of exciting science opportunities for space physics and aeronomy. They all have thin atmospheres with residence times of a few days at most. The surface interactions with the space environment determine the atmospheric and ionospheric properties. The Jupiter Icy Moons Orbiter (JIMO) gives possibilities to investigate the weathering properties of their surfaces and volatile material expelled from their interiors. The atmospheres and the ionized ionospheric components of the Galilean moons (including the volcanic moon Io) interact strongly with the co-rotating magnetosphere of Jupiter. This interaction is dynamic and for example triggers energy transfer processes that give rise to auroral signatures at Jupiter. The icy moon’s ionospheres are likewise highly variable in time and estimated peak electron densities vary between 1000 and 20,000 cm −3 near their surfaces. A particularly interesting interaction occurs between the magnetosphere of Jupiter and the mini-magnetosphere of Ganymede and its ionosphere. A double-Langmuir probe (LP) experiment orbiting the moons at a short distance for several months will give valuable insight into these processes. Foremost the LP measures in situ plasma density and temperatures of the ionospheric components of the moons with high time resolution and thereby provides estimates of key parameters for the dynamical behaviour of surface weathering and magnetospheric influences. In addition many other physical parameters important to the dynamics of these systems can be estimated with such an instrument, like the plasma flow and the DC electric field. Recent results from the LP part of the Radio and Plasma Wave Science (RPWS) on board the Cassini/Huygens spacecraft orbiting Saturn show that an LP works in extended plasma parameter domains with very good science return.

DYNAMO: a Mars upper atmosphere package for investigating solar wind interaction and escape processes, and mapping Martian fields

DYNAMO is a small multi-instrument payload aimed at characterizing current atmospheric escape, which is still poorly constrained, and improving gravity and magnetic field representations, in order to better understand the magnetic, geologic and thermal history of Mars. The internal structure and evolution of Mars is thought to have influenced climate evolution. The collapse of the primitive magnetosphere early in Mars history could have enhanced atmospheric escape and favored transition to the present arid climate. These objectives are achieved by using a low periapsis orbit. DYNAMO has been proposed in response to the AO released in February 2002 for instruments to be flown as a complementary payload onboard the CNES Orbiter to Mars (MO-07), foreseen to be launched in 2007 in the framework of the French PREMIER Mars exploration program. MO-07 orbital phase 2b (with an elliptical orbit of periapsis 170 km), and in a lesser extent 2a, offers an unprecedented opportunity to investigate by in situ probing the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, and therefore the present atmospheric escape rate. Ultraviolet remote sensing is an essential complement to characterize high, tenuous, layers of the atmosphere. One Martian year of operation, with about 5,000 low passes, should allow DYNAMO to map in great detail the residual magnetic field, together with the gravity field. Additional data on the internal structure will be obtained by mapping the electric conductivity, sinergistically with the NETLANDER magnetic data. Three options have been recommended by the International Science and Technical Review Board (ISTRB), who met on July 1st and 2nd, 2002. One of them is centered on DYNAMO. The final choice, which should be made before the end of 2002, will depend on available funding resources at CNES.

MEP (Mars Environment Package): toward a package for studying environmental conditions at the surface of Mars from future lander/rover missions

In view to prepare Mars human exploration, it is necessary to promote and lead, at the international level, a highly interdisciplinary program, involving specialists of geochemistry, geophysics, atmospheric science, space weather, and biology. The goal of this program will be to elaborate concepts of individual instruments, then of integrated instrumental packages, able to collect exhaustive data sets of environmental parameters from future landers and rovers of Mars, and to favour the conditions of their implementation. Such a program is one of the most urgent need for preparing human exploration, in order to develop mitigation strategies aimed at ensuring the safety of human explorers, and minimizing risk for surface operations. A few main areas of investigation may be listed: particle and radiation environment, chemical composition of atmosphere, meteorology, chemical composition of dust, surface and subsurface material, water in the subsurface, physical properties of the soil, search for an hypothesized microbial activity, characterization of radio-electric properties of the Martian ionosphere. Scientists at the origin of the present paper, already involved at a high degree of responsibility in several Mars missions, and actively preparing in situ instrumentation for future landed platforms (Netlander—now cancelled, MSL-09), express their readiness to participate in both ESA/AURORA and NASA programs of Mars human exploration. They think that the formation of a Mars Environment working group at ESA, in the course of the AURORA definition phase, could act positively in favour of the program, by increasing its scientific cross-section and making it still more focused on human exploration.

The applicability of advanced ionosondes to the IRI

The ionosonde has evolved from the early analog film-recording depictor of the ionosphere, into a precision diagnositic instrument. Contemporary monitoring ionosondes occupy an intermediate niche in this evolution. Some of these present digital ionogram images to interpretation experts who use the conveniences of digital data presentation to identify and record parameter values. This approach can improve parameter precision, but it remains as labor intensive as in the days of film recording. Other monitoring in accuracy compared to manual analysis. The reduction in accuracy is often unquantified, which can introduce unknown errors into the IRI and other ionosphere models. Autoscaling algorithms have not succeeded to duplicate expert judgments because, in part, of the limited information available from contemporary monitoring instruments. Advanced digital ionosondes can make up this difference, and much more, with precision measurements of all available echo properties. Automated data reduction algorithms can use these measurements to improve the accuracy and continuity of established parameters, and to develop new diagnostic capabilities for a wider variety of ionospheric properties. These improvements are essential for the continuing development of ionospheric models such as the IRI.

Lower ionospheric modification by lightning‐EMP: Simulation of the night ionosphere over the United States

It has recently been suggested that successive intense lightning‐electromagnetic pulse (EMP) events could cause significant large‐scale changes to the properties of the nighttime lower ionosphere. In order to examine this quantitatively, data on lightning detected over the United States are combined with the output from a simulation code. During the course of a night strong lightning‐EMP events can lead to significant (∼100% or even greater) increases in the electron density of the lower ionosphere, with the largest increases at ∼90 km altitude. Regions with significant decreases in electron density are also possible. It is shown that changes in the electron temperature of the lower ionosphere are unlikely to be significant. The time required to produce large‐scale changes of ionospheric electron density above an active thunderstorm may explain the observation of a thunderstorm “modification time” before red sprite activity is initiated.

Scientific objectives of the DYNAMO mission

DYNAMO is a small Mars orbiter planned to be launched in 2005 or 2007, in the frame of the NASA/ CNES Mars exploration program. It is aimed at improving gravity and magnetic field resolution, in order to better understand the magnetic, geologic and thermal history of Mars, and at characterizing current atmospheric escape, which is still poorly constrained. These objectives are achieved by using a low periapsis orbit, similar to the one used by the Mars Global Surveyor spacecraft during its aerobraking phases. The proposed periapsis altitude for DYNAMO of 120–130 km, coupled with the global distribution of periapses to be obtained during one Martian year of operation, through about 5000 low passes, will produce a magnetic/gravity field data set with approximately five times the spatial resolution of MGS. Additional data on the internal structure will be obtained by mapping the electric conductivity. Low periapsis provides a unique opportunity to investigate the chemical and dynamical properties of the deep ionosphere, thermosphere, and the interaction between the atmosphere and the solar wind, therefore atmospheric escape, which may have played a crucial role in removing atmosphere and water from the planet.

Nonlinear model of short-scale electrodynamics in the auroral ionosphere

Abstract. The optical detection of auroral subarcs a few tens of m wide as well as the direct observation of shears several m/s per m over km to sub km scales by rocket instrumentation both indicate that violent and highly localized electrodynamics can occur at times in the auroral ionosphere over scales 100 m or less in width. These observations as well as the detection of unstable ion-acoustic waves observed by incoherent radars along the geomagnetic field lines has motivated us to develop a detailed time-dependent two-dimensional model of short-scale auroral electrodynamics that uses current continuity, Ohm's law, and 8-moment transport equations for the ions and electrons in the presence of large ambient electric fields to describe wide auroral arcs with sharp edges in response to sharp cut-offs in precipitation (even though it may be possible to describe thin arcs and ultra-thin arcs with our model, we have left such a study for future work). We present the essential elements of this new model and illustrate the model's usefulness with a sample run for which the ambient electric field is 100 mV/m away from the arc and for which electron precipitation cuts off over a region 100 m wide. The sample run demonstrates that parallel current densities of the order of several hundred µA m-2 can be triggered in these circumstances, together with shears several m/s per m in magnitude and parallel electric fields of the order of 0.1 mV/m around 130 km altitude. It also illustrates that the local ionospheric properties like densities, temperature and composition can strongly be affected by the violent localized electrodynamics and vice-versa.Key words: Ionosphere (auroral ionosphere, electric fields and currents, ionosphere-magnetosphere interactions)

Nonlinear model of short-scale electrodynamics in the auroral ionosphere

The optical detection of auroral subarcs a few tens of m wide as well as the direct observation of shears several m/s per m over km to sub km scales by rocket instrumentation both indicate that violent and highly localized electrodynamics can occur at times in the auroral ionosphere over scales 100 m or less in width. These observations as well as the detection of unstable ion-acoustic waves observed by incoherent radars along the geomagnetic field lines has motivated us to develop a detailed time-dependent two-dimensional model of short-scale auroral electrodynamics that uses current continuity, Ohm's law, and 8-moment transport equations for the ions and electrons in the presence of large ambient electric fields to describe wide auroral arcs with sharp edges in response to sharp cut-offs in precipitation (even though it may be possible to describe thin arcs and ultra-thin arcs with our model, we have left such a study for future work). We present the essential elements of this new model and illustrate the model's usefulness with a sample run for which the ambient electric field is 100 mV/m away from the arc and for which electron precipitation cuts off over a region 100 m wide. The sample run demonstrates that parallel current densities of the order of several hundred µA m-2 can be triggered in these circumstances, together with shears several m/s per m in magnitude and parallel electric fields of the order of 0.1 mV/m around 130 km altitude. It also illustrates that the local ionospheric properties like densities, temperature and composition can strongly be affected by the violent localized electrodynamics and vice-versa.Key words: Ionosphere (auroral ionosphere, electric fields and currents, ionosphere-magnetosphere interactions)

Modeling of the thermosphere-ionosphere system

Empirical, semi-empirical, and theoretical models of the thermosphere and ionosphere and of photochemical processes occurring therein are briefly described. An overview is provided of this section of the issue, containing papers on these topics and on the measurement of thermospheric and ionospheric properties from space. The importance to these endeavors of accurate measurement and specification of the solar ultraviolet, extreme-ultraviolet, and soft x-ray irradiance is discussed.

A model analysis of Galileo electron densities on Jupiter

A one‐dimensional chemical‐diffusive model of the Jovian ionosphere, in conjunction with measured upper atmospheric temperatures, is used to analyze the upper ionospheric electron densities on Jupiter measured by the Galileo RSS instrument on December 8, 1995. The analyses of these measurements have yielded quite different ionospheric properties at ingress and egress in terms of both the magnitude and the altitude of the peak electron density (ne). At ingress, the peak ne was ∼105 cm−3 at an altitude of ∼900 km. However, at egress the ne peak was ∼5 times smaller than at ingress and was located at ∼1800 km altitude. As with our previous studies, we find it necessary to invoke a combination of vibrationally excited H2 and vertical plasma flow to explain the measured ionospheric structure. The most interesting conclusion of this study is that a downward drift of plasma is required to fit the peak altitude of the ingress ne profile. The direction of the vertical flow is most likely determined by the horizontal neutral wind. At egress, the situation is quite different because a strong field‐aligned drift of 90 m/s, most likely caused by the meridional component of the neutral wind, is required to maintain the peak ne at the measured altitude. The role of vibrationally excited H2 in determining the magnitude of the measured ne appears to be less important at ingress than at egress.

External supply of oxygen to the atmospheres of the giant planets.

The atmospheres of the giant planets are reducing, being mainly composed of hydrogen, helium and methane. But the rings and icy satellites that surround these planets, together with the flux of interplanetary dust, could act as important sources of oxygen, which would be delivered to the atmospheres mainly in the form of water ice or silicate dust. Here we report the detection, by infrared spectroscopy, of gaseous H2O in the upper atmospheres of Saturn, Uranus and Neptune. The implied H2O column densities are 1.5 x 10(15), 9 x 10(13) and 3 x 10(14) molecules cm(-2) respectively. CO2 in comparable amounts was also detected in the atmospheres of Saturn and Neptune. These observations can be accounted for by external fluxes of 10(5)-10(7) H2O molecules cm(-2) s(-1) and subsequent chemical processing in the atmospheres. The presence of gaseous water and infalling dust will affect the photochemistry, energy budget and ionospheric properties of these atmospheres. Moreover, our findings may help to constrain the injection rate and possible activity of distant icy objects in the Solar System.