A Science Mission for QSAT Project: Study of FACs in the Polar and Equatorial Regions

Kyushu University, Kyushu Institute of Technology and Fukuoka Institute of Technology are now designing, developing and building a micro-satellite called “QSAT”. The primary objective of QSAT is understanding the mechanism of spacecraft charging, which can be achieved with the onboard magnetometer, high-frequency probe (HP) and Langmuir probe (LP). The magnetometer measures the magnetic field variations caused by field-aligned currents (FACs) in the polar and equatorial regions. Polar FACs are well understood, while equatorial FACs are not. The science goals are as follows: (1) to better understand FACs in the polar region, (2) to compare the FACs observed in orbit with ground-based MAGDAS observations, (3) to investigate spatial distribution of FACs in the equatorial region. FACs play a crucial role in the coupling between solar wind, magnetosphere and ionosphere in terms of energy transfer. Also if we understand the relationship between the space and ground-based FACs data, then we can conduct long-term study on the solar wind–magnetosphere–ionosphere coupling in the future by mainly using data from ground-based magnetometer arrays.     

International Heliophysical Year 2007: A Report from the UN/NASA Workshop Bangalore, India, 27 November–1 December 2006

The IHY Secretariat and the United Nations Basic Space Science Initiative (UNBSSI) assist scientists and engineers from all over the world in participating in the International Heliophysical Year (IHY) 2007. A major thrust of IHY/UNBSSI is to deploy arrays of small, inexpensive instruments such as magnetometers, radio telescopes, GPS receivers, all-sky cameras, etc. around the world to allow global measurements of ionospheric and heliospheric phenomena. The small instrument programme is envisioned as a partnership between instrument providers and instrument hosts in developing nations. The IHY/UNBSSI can facilitate the deployment of several of these networks world-wide. Existing data bases and relevant software tools will be identified to promote space science activities in developing nations. Extensive data on space science have been accumulated by a number of space missions. Similarly, long-term data bases are available from ground-based observations. These data can be utilized in ways different from originally intended for understanding the heliophysical processes. This paper provides a comprehensive overview of IHY/UNBSSI, its achievements, future plans, and outreach to the 192 Member States of the United Nations as recorded in the UN/NASA workshop in India.     

The Remote Equatorial Nighttime Observatory of Ionospheric Regions Project and the International Heliospherical Year

We describe a new suite of instruments planned for deployment to Cape Verde as part of the International Heliospherical Year. The Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) project consists of a bistatic Fabry–Perot interferometer system, an all-sky imaging system, a dual-frequency Global Positioning System (GPS) receiver, and an array of single-frequency GPS scintillation monitors. This instrumentation will allow for studying the low-latitude thermosphere/ionosphere (TI) system in great detail. Investigations to be conducted using this instrumentation while in Cape Verde include studying equatorial irregularity processes, the effects of neutral winds and gravity waves on irregularity development, the midnight temperature maximum, and ion-neutral coupling in the nighttime TI system. Initial observations from the RENOIR instrumentation during pre-deployment testing at the Urbana Atmospheric Observatory are presented, as is the deployment scenario for the project in Cape Verde.     

Modeling African equatorial ionosphere using ordinary Kriging interpolation technique for GNSS applications

The ability to model the ionosphere accurately for single frequency users in satellite applications has gained some appreciable usage, most especially during quiet conditions in a mild (middle latitudes) ionosphere. However, solving the problem of ionosphere for single frequency user of Global Navigation Satellite Systems (GNSS) in equatorial ionization anomaly (EIA) region is of a great concern for space scientists and engineers. Several methodologies have been used to develop models that describe global or regional maps for ionosphere errors in order to mitigate the effect of the errors on GNSS systems. Global or regional ionosphere Maps have been known to be an efficient tool to monitor the delay introduced by the ionosphere in the satellite signals. This research uses the conventional Planar fit and ordinary Kriging methodologies to assess a regional map for ionosphere correction in equatorial African sector. The result obtained is an indication that modified Kriging methodology describes the EIA ionosphere corrections better compared with ordinary Kriging and Planar fit methodologies.     

Transient ULF pulsation decay rates observed by ground based magnetometers: The contribution of spatial integration

Theoretical studies suggest that Joule dissipation in the ionosphere is the major source of damping for resonant ULF pulsations. The decay rates of transient pulsations (i.e. short-lived pulsations with latitude dependent periods) observed by ground based magnetometers are however generally larger than those predicted, and also larger than those observed in the magnetosphere. We have modelled the integration effects of ground based magnetometers on transient pulsations by considering empirical models of the associated ionospheric currents. The simulated ground magnetometer data show a smearing of the amplitude and period variations, which is more pronounced for smaller scale (specifically latitudinal) variations. The period increase with latitude is reduced, and may even be eliminated over appreciable latitude ranges. For all spatial scales the observed decay rates are typically 2–3 times larger than the true values, due to the additional decay resulting from spatial integration of the incoherent transient pulsations. Estimates of the ionospheric Pedersen conductance based on ground magnetometer observations of decay rates are correspondingly too small, and spurious gradients may be introduced. The present calculations reconcile observed decay rates on the ground with those predicted using the assumption that Joule dissipation is the dominant damping mechanism for toroidal mode resonant oscillations.     

Disappearing ionospheres on the nightside of Venus

Instruments on the Pioneer Venus Orbiter have detected a substantial ionosphere on the nightside of Venus during most orbits. However, during some orbits the nightside ionosphere seems to have almost disappeared, existing only as irregular patches of low-density plasma. The solar wind dynamic pressure on these occasions is greater than average. We have correlated data from several instruments (Langmuir probe, ion mass spectrometer, retarding potential analyzer, magnetometer, and plasma analyzer) for a number of orbits during which the nightside ionosphere had disappeared. The magnetic field tends to be coherent, horizontal, and larger than usual, and the electron and ion temperatures are much larger than they usually are on the nightside. We suggest mechanisms which might explain the reasons for the disappearance of the ionosphere when the solar wind dynamic pressure is large.     

Agreements between ground-based and satellite-based observations

On the basis of records from meridian chains of magnetometers and the KRM inversion method, we have deduced a number of ionospheric quantities, including the distribution of the electric potential, field-aligned currents, the ionospheric currents and its equatorial counterpart and the relationship between the AE index and the cross-polar cap potential. In this paper, we examine the results thus obtained in the light of compatible data which are deduced from satellite observations. It is shown that both results agree fairly well, proving the validity of the polar ionospheric parameters deduced from both the ground-based and satellite-based data. Several important implications of the results are pointed out.     

The influence of the equatorial anomaly on the ground reception of non-ducted whistlers at low latitudes

It is the purpose of this paper to study whether the non-ducted propagation in the inner plasmasphere in the presence of the equatorial anomaly might be relevant to daytime whistlers observed on the ground at low latitudes. Realistic models of the equatorial anomaly simulating the satellite observations have been incorporated in the ray tracing computations. It is found that there are two different non-ducted modes able to penetrate through the ionosphere onto the ground; (1) whispering gallery mode around the anomaly field line which is trapped just by the outer boundary of the anomaly, and (2) pro-longitudinal (PL) mode at a latitude around 30° which is supported by the horizontal gradient in the tail of the anomaly. These modes may provide a new interpretation for some whistlers observed on the ground. The properties of these modes are examined in detail and then compared with those of ducted propagation. This study may be useful for distinguishing the propagation mode in future ground-based experiments.     

Observations of ELF electromagnetic waves associated with equatorial spread F

Extreme low frequency electromagnetic waves have been observed below the F peak in the equatorial ionosphere by instruments onboard OGO-6. Electrostatic wave observations indicate that the steep gradient was unstable to the process which causes equatorial spread F above the region where the electromagnetic waves were observed. The data are very similar to observations near the polar cusp and give further evidence that ELF waves are excluded from regions of rapid and irregular density increases. Low level electromagnetic waves with similar properties were occasionally observed on the nightside by the OVI-17 electric field sensor and may be plasmaspheric hiss which has propagated to low altitude.     

QSAT: The Satellite for Polar Plasma Observation

This paper introduces QSAT, the satellite for polar plasma observation. The QSAT project began in 2006 as an initiative by graduate students of Kyushu University, and has the potential to contribute greatly to IHY (International Heliophysical Year) by showing to the world the beauty, importance, and relevance of space science. The primary objectives of the QSAT mission are (1) to investigate plasma physics in the Earth’s aurora zone in order to better understand spacecraft charging, and (2) to conduct a comparison of the field-aligned current observed in orbit with ground-based observations. The QSAT project can provide education and research opportunities for students in an activity combining space sciences and satellite engineering. The QSAT satellite is designed to be launched in a piggyback fashion with the Japanese launch vehicle H-IIA. The spacecraft bus is being developed at the Department of Aeronautics and Astronautics of Kyushu University with collaboration of Fukuoka Institute of Technology. Regarding the payload instruments, the Space Environment Research Center of Kyushu University is developing the magnetometers, whereas the Laboratory of Spacecraft Environment Interaction Engineering of Kyushu Institute of Technology is developing the plasma probes. We aim to be ready for launch in 2009 or later.     

Saturn's cloud morphology and zonal winds before the Cassini encounter

Analyses of Hubble Space Telescope (HST) images of Saturn obtained from August 2003 to March 2004, with extensive support from ground-based telescopes, have been used to characterize the cloud morphology and motions in its atmosphere few months before the Cassini encounter. We present data on the major meteorological features as potential targets for Cassini observations. We extend our previous measurements of the zonal winds during the 1996-2002 period (A. Sánchez-Lavega et al., 2003, Nature, 423, 623-625), confirming the strong change in the equatorial jet, and the high hemispheric symmetry of the zonal wind pattern.     

Study of total electron content variations over equatorial and low latitude ionosphere during extreme solar minimum

In recent years with the advancement in satellite based navigational applications, study of Total Electron Content (TEC) has gained significant importance. It is well known that due to dynamical behaviour of equatorial and low latitude ionosphere, the levels of ionization is relatively high herein. The sustained decrease in solar extreme ultraviolet radiations during the current minimum is greater than any in recent history. This gives us the opportunity to study the observations of global positioning system total electron content (GPS-TEC) dual frequency signals from the GPS satellites continuously recorded at Trivandrum (an equatorial station) and Delhi (a low latitude station) during the extremely low solar activity period from January 2007 to June 2009. This study illustrates the diurnal, seasonal and annual variations of TEC during the extended solar minimum period. This study also investigates the behaviour of daytime ionosphere around spring and autumn equinoxes at low solar activity period. The results clearly reveal the presence of equinoctial asymmetry which is more pronounced at equatorial station Trivandrum. The diurnal variation of TEC shows a short-lived day minimum which occurs between 0500 to 0600 LT at both the stations. Delhi TEC values show its steep increase and reach at its peak value between 1200 and 1400 LT, while at the equator the peak is broad and occurs around 1600 LT. Further, the daily maximum TEC ranges from about 5 to 40 TEC units at Trivandrum and about 10 to 40 TEC units at Delhi, which correspond to range delay variations of about 1 to 8 m at the GPS L1 frequency of 1.575 GHz. The Maximum values of TEC were observed during spring equinox rather than autumn equinox, showing presence of semi annual variation at both the locations. The minimum values of TEC were observed during the summer solstice at Trivandrum indicating the presence of winter anomaly at equatorial region while Delhi TEC values were minimum during winter solstice showing absence of winter anomaly. Also the TEC values at both the locations have been decreasing since 2007 onwards exhibit good positive correlation with solar activity.     

Atmospheric loss of energetic electrons in the Jovian synchrotron zone

For decades, ground-based radio observations of Jovian synchrotron radiation have shown emission originating predominantly from the equatorial region and from high-latitude regions (lobes) near L∼2.5. The observations show a longitudinally asymmetric gap between the emission peaks of the lobes and the atmosphere of Jupiter. One possible explanation for these gaps is the loss of electrons through collisions with atmospheric neutrals as the electrons bounce along magnetic field lines and drift longitudinally in the presence of asymmetric magnetic fields. To assess this hypothesis, we applied the recently developed O6 and VIP4 magnetic field models to calculate the trajectories of electrons as they drift longitudinally in Jupiter's magnetic field, and derive the sizes of their equatorial drift loss cones. We then identified the shells on which electrons would be lost due to collisions with the atmosphere. The calculated drift loss cone sizes could be applied in future to the modeling of electron distribution functions in this region and could also be applied to the study of Jovian auroral zone. This method also allowed us to compute the shell-splitting effects for these drifting electrons and we find the shell-splitting to be small (?0.05R_J). This justifies a recent modeling assumption that particles drift on the same shells in a three-dimensional distribution model of electrons. We also compared the computed gaps with the observed gaps, and found that the atmospheric loss mechanism alone is not able to sufficiently explain the observed gap asymmetry.     

Plasmaspheric hiss observed in the topside ionosphere at mid- and low-latitudes

Latitudinal characteristics of ELF hiss in mid- and low-latitudes have been statistically studied by using ELF/VLF electric field spectra (50 Hz-30 kHz) from ISIS-1 and -2 received at Kashima station, Japan from 1973 to 1977. Most ISIS ELF/VLF data observed in mid- and low-latitude include ELF hiss at frequencies below a few kHz. The ELF hiss has the strongest intensity among VLF phenomena observed by the ISIS electric dipole antenna in mid- and low-latitudes, but the ELF hiss has no rising structure like the chorus in the detailed frequency-time spectrum. The ELF hiss is classified into the steady ELF hiss whose upper frequency limit is approximately constant with latitude and the ELF hiss whose upper frequency limit increases with latitude. These two types of ELF hiss occur often in medium or quiet geomagnetic activities. Sometimes there occurs a partial or complete lack of ELF hiss along an ISIS pass.Spectral shape and bandwidth of ELF hiss in the topside ionosphere are very similar to those of plasmaspheric hiss and of inner zone hiss. The occurrence rate of steady ELF hiss is about 0.3 near the geomagnetic equator and decreases rapidly with latitude around L = 3. Hence it seems likely that ELF hiss is generated by cyclotron resonant instability with electrons of several tens of keV in the equatorial outer plasmasphere beyond L = 3.Thirty-seven per cent of ELF hiss events received at Kashima station occurred during storm times and 63% of them occurred in non-storm or quiet periods. Sixty-seven per cent of 82 ELF hiss events during storm times were observed in the recovery phase of geomagnetic storms. This agrees with the previous satellite observations of ELF hiss by search coil magnetometers. The electric field of ELF hiss becomes very weak every 10 s, which is the satellite spin period, in mid- and low-latitudes, but not near the geomagnetic equator. Ray tracing results suggest that waves of ELF hiss generated in the equatorial outer plasmasphere propagate down in the electrostatic whistler mode towards the equatorial ionosphere, bouncing between the LHR reflection points in both the plasmaspheric hemispheres.     

An agile very low frequency radio spectrum explorer

The very low frequency(VLF) regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources,transients,and so on.However,the nontransparency of the Earth's ionosphere,ionospheric distortion and artificial radio frequency interference(RFI) have made it difficult to detect the VLF celestial radio emission with ground-based instruments.A straightforward solution to overcome these problems is a space-based VLF radio telescope,just like the VLF radio instruments onboard the Chang'E-4 spacecraft.But building such a space telescope would be inevitably costly and technically challenging.The alternative approach would be then a ground-based VLF radio telescope.Particularly,in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a 'calm' state,it will provide us a good chance to perform VLF ground-based radio observations.Anticipating such an opportunity,we built an agile VLF radio spectrum explorer co-located with the currently operational Mingantu Spectra Radio Heliograph(MUSER).The instrument includes four antennas operating in the VLF frequency range 1-70 MHz.Along with them,we employ an eight-channel analog and digital receivers to amplify,digitize and process the radio signals received by the antennas.We present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions.     

The role of ground arrays of magnetometers in the study of pulsation resonance regions

The last ten years have seen significant progress in the understanding of magnetic pulsations. Results from ground arrays of magnetometers were instrumental in the establishment of the concept of field line resonance, which has proved essential to the ordering of observed pulsation phenomena. Ground arrays have continued to be indispensable in the study of pulsation resonance regions. In this paper we will review the major contributions that ground arrays have made in the areas of field line resonance inside and outside the plasmasphere, the role of the plasmapause, azimuthal propagation, the effect of the ionosphere and correlation with satellite observations. Emphasis will be on recent developments and we will also make some suggestions for possible array work in the future.     

The topside equatorial ionosphere during daytime: Elevated plasma temperatures,the transequatorial O+ breeze and the dynamics of minor ions

Steady-state calculations are performed for the daytime equatorial F2-region and topside ionosphere. Values are calculated of the electron and ion temperatures and the concentrations and field-aligned velocities of the ions O⁺, H⁺ and He⁺. Account is taken of upward $\text{E × B}$ drift, a summer-winter horizontal neutral air wind and heating of the electron gas by thermalization of fast photoelectrons.The calculated plasma temperatures are in accord with experiment: at the equator there is an isothermal region from about 400–550 km altitude, with temperatures of about 2400 K around 800 km altitude. The transequatorial O⁺ breeze flux from summer to winter in the topside ionosphere is not greatly affected by the elevated plasma temperatures. The field-aligned velocities of H⁺ and He⁺ depend strongly on the O⁺ field-aligned velocity and on the presence of large temperature gradients. For the minor ions, ion-ion drag with O⁺ cannot be neglected for the topside ionosphere.     

Proposal to Use MAGDAS/CPMN to Study the Equatorial Electrojet: A Philippine Contribution to the International Heliophysical Year

As a Philippine contribution to the International Heliophysical Year, we propose to use the MAGnetic Data Acquisition System/Circum Pan-Pacific Magnetometer Network (MAGDAS/CPMN), installed by the Space Environment Research Center (SERC), Kyushu University along the 210° magnetic meridian and the magnetic equator, to study the equatorial electrojet (EEJ) and counter electrojet (CEJ). Through this installation, it is made possible to observe geomagnetic field variations in real time. By utilizing this network of ground-based instruments, we hope to elucidate their regular day-to-day and seasonal variabilities and variations during magnetic storms and substorms. We also want to study the behavior of this ionospheric current system before, during, and after the occurrence of an earthquake.     

The effect of finite ionosphere conductivities on axisymmetric toroidal Alfvén wave resonances

Previously developed solutions for pure toroidal mode Alfvén waves with finite ionosphere conductivities are modified to apply both inside and outside the plasmapause.Detailed diagrams are provided to illustrate the effect of realistic ionosphere conductances on the wave-forms. As well as graphs of wave-period, these include: (a) half-wave solutions showing the effect of dipole field distortion and consequent enhancement of ionosphere electric fields; (b) half-wave solutions with low damping that are symmetric and asymmetric about the equatorial plane; (c) highly-damped half-wave and quarter-wave solutions with wave admittance at the ionosphere nearly equal to the ionosphere conductance; (d) a quarter-wave solution with low damping that has a “near-node” of electric field at one ionosphere and an antinode of electric field at the other.     

Spatial and temporal structure of a high-latitude transient ULF pulsation

Auroral radar observations of transient ULF pulsations with latitudinally varying period have recently been reported. An event of this type is analysed using data from the Scandinavian Magnetometer Array, the STARE radar, and the GEOS-2 satellite. The magnetometers show long-period (～450 s) oscillations consistent with the pulsations observed in the ionosphere using STARE, and confirm that the geomagnetic field shells are resonating in the toroidal mode. There is also a localised, small-amplitude component with 250-s period South of the STARE pulsations. Electric field measurements at GEOS-2 show only an impulsively stimulated pulsation of 250-s period. The wave fields at GEOS-2 imply that the satellite was earthward of a localised toroidal standing-wave resonance, which mapped to the ionosphere at least one degree South of the expected position. A radial profile of equatorial plasma mass density is inferred from the GEOS-2 and STARE results. This shows a radially increasing density near GEOS-2, and a radially decreasing density outside the satellite position.An interpretation of the event is given in which a tailward propagating hydromagnetic impulse directly stimulates field shells outside 7 R_E to oscillate at their eigenperiods. In the region of increasing density near GEOS-2, a relatively highly-damped surface wave is excited. This feeds energy rapidly into a narrow monochromatic toroidal field-line resonance, which subsequently decays more slowly through ionospheric dissipation.