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The 13th Symposium on Polar Science/Ordinary sessions [OS] Space and upper atmospheric sciences, Wed. 16 Nov.

The 12th Symposium on Polar Science, 15–18 Nov. 2021, National Institute of Polar Research (NIPR) Research Organization of Information and Systems (ROIS)

We demonstrate that the Super Dual Auroral Radar Network (SuperDARN) radar at Syowa station, Antarctica, can be used to detect high frequency radio wave attenuation in the D region ionosphere during energetic electron precipitation (EEP) events. EEP‐related attenuation is identified in the radar data as a sudden reduction in the backscatter power and background noise parameters. We focus initially on EEP associated with pulsating aurora and use images from a colocated all‐sky camera as a validation data set for the radar‐based EEP event detection method. Our results show that high‐frequency attenuation that commences during periods of optical pulsating aurora typically continues for 2–4 hr after the camera stops imaging at dawn. We then use the radar data to determine EEP occurrence rates as a function of magnetic local time (MLT) using a database of 555 events detected in 2011. EEP occurrence rates are highest in the early morning sector and lowest at around 15:00–18:00 MLT. The postmidnight and morning sector occurrence rates exhibit significant seasonal variations, reaching approximately 50% in the winter and 15% in the summer, whereas no seasonal variations were observed in other MLT sectors. The mean event lifetime determined from the radar data was 2.25 hr, and 10% of events had lifetimes exceeding 5 hr.

The 11th Symposium on Polar Science/Special session: [S] Accelerating Arctic research: Recent progress and future prospect of Arctic research, Tue. 1 Dec.

A specialized ground-based system has been developed for simultaneous observations of pulsating aurora (PsA) and related magnetospheric phenomena with the Arase satellite. The instrument suite is c...

As the EISCAT UHF radar system in Northern Scandinavia started its operations in the early 1980s, the collected data cover about three solar cycles. These long time-series provide us the opportunity to study long-term variations and trends of ionospheric parameters in the high latitude region. In the present study we have used the EISCAT Tromso UHF data to investigate variations of the Hall conductivity and ion temperatures in the E-region around noon. Both the ion temperature and the peak altitude of the Hall conductivity are confirmed to depend strongly on solar zenith angle. However, the dependence on solar activity seems to be weak. In order to search for trends in these parameters, the ion temperature and peak altitude of the Hall conductivity data were adjusted for their seasonal and solar cycle dependence. A very weak descent (∼0.2 km/ decade) was seen in the peak altitude of the Hall conductivity. The ion temperature at 110 km shows a cooling trend (∼10 K/ decade). However, other parameters than solar zenith angle and solar activity seem to affect the ion temperature at this altitude, and a better understanding of these parameters is necessary to derive a conclusive trend. In this paper, we discuss what may cause the characteristics of the variations in the electric conductivities and ion temperatures in the high latitude region.

The Tenth Symposium on Polar Science/Ordinary sessions: [OS] Space and upper atmospheric sciences, Wed. 4 Dec. / Institute of Statistics and Mathematics (ISM) Seminar room 2 (D304) (3rd floor)

This paper introduces a new system that can monitor aurora and atmospheric airglow using a low-cost Watec monochromatic imager (WMI) equipped with a sensitive camera, a filter with high transmittance, and the non-telecentric optics. The WMI system with 486-nm, 558-nm, and 630-nm band-pass filters has observable luminosity of about ~200–4000 Rayleigh for 1.07-sec exposure time and about ~40–1200 Rayleigh for 4.27-sec exposure time, for example. It is demonstrated that the WMI system is capable of detecting 428-nm auroral intensities properly, through comparison with those measured with a collocated electron-multiplying charge-coupled device (EMCCD) imager system with narrower band-pass filter. The WMI system has two distinct advantages over the existing system: One makes it possible to reduce overall costs, and the other is that it enables the continuous observation even under twilight and moonlight conditions. Since 2013 a set of multi-wavelength WMIs has been operating in northern Scandinavia, Svalbard, and Antarctica to study meso- and large-scale aurora and airglow phenomena. Future development of the low-cost WMI system is expected to provide a great opportunity for constructing a global network for multi-wavelength aurora and airglow monitoring.

The Ninth Symposium on Polar Science/Ordinary sessions: [OS] Space and upper-atmosphere sciences, Wed. 5 Dec. / 3F Seminar room D304, Institute of Statistics and Mathematics

18th EISCAT symposiumSession E4: Aurora and airglowMay 30 (Tue), Poster Session

18th EISCAT symposiumSession E6: The ERG mission and magnetosphere-ionosphere couplingMay 27 (Sat), Poster Session

18th EISCAT symposiumSession E3: Ionoshere/thermosphere/mesosphereMay 27 (Sat), NIPR Auditorium

18th EISCAT symposiumSession E6: The ERG mission and magnetosphere-ionosphere couplingMay 26 (Fri), NIPR Auditorium

第7回極域科学シンポジウム:[OS]宙空圏11月29日（火）統計数理研究所 3階 セミナー室D305

Aurora Computed Tomography (ACT) is a method for retrieving the three-dimensional (3-D) distribution of the volume emission rate from monochromatic auroral images obtained simultaneously by a multi-point camera network. We extend this method to a Generalized-Aurora Computed Tomography (G-ACT) that reconstructs the energy and spatial distributions of precipitating electrons from multi-instrument data, such as ionospheric electron density from incoherent scatter radar, cosmic noise absorption (CNA) from imaging riometers, as well as the auroral images. The purpose of this paper is to describe the reconstruction algorithm involved in this method and to test its feasibility by numerical simulation. Based on a Bayesian model with prior information as the smoothness of the electron energy spectra, the inverse problem is formulated as a maximization of posterior probability. The relative weighting of each instrument data is determined by the cross-validation method. We apply this method to the simulated data from real instruments, the Auroral Large Imaging System (ALIS), the European Incoherent Scatter (EISCAT) radar at Tromsø, and the Imaging Riometer for Ionospheric Study (IRIS) at Kilpisjärvi. The results indicate that the differential flux of the precipitating electrons is well reconstructed from the ALIS images for the low-noise cases. Furthermore, we demonstrate in a case study that the ionospheric electron density from the EISCAT radar is useful for improving the reconstructed electron flux. On the other hand, the incorporation of CNA data into this method is difficult at this stage, because the extension of energy range to higher energy causes a difficulty in the reconstruction of the low-energy electron flux. Nevertheless, we expect that this method may be useful in analyzing multi-instrument data and, in particular, 3-D data, which will be obtained in the upcoming EISCAT_3D.

In order to study the generation and propagation processes of MF auroral radio emissions (referred to as auroral roar and MF burst) in the polar ionosphere, an Auroral Radio Spectrograph (ARS) system was installed at Husafell station in Iceland (invariant latitude: 65.3°). Data analysis of man-made transmissions also provides useful information for the ionosphere study as well as an investigation of auroral radio emissions since the propagation character of MF radio waves changes depending on electron-neutral collisions in the bottomside ionosphere. Thus, ionospheric absorption is examined in comparison with the solar zenith angle and auroral phenomena. The results indicate that the ARS data can be used to detect ionization occurring at distant regions. In late 2006, the ARS detected one auroral roar and twoMF bursts, which were identified as left-handed polarized waves. Results of data analysis, including other auroral data and particle spectra observed by the DMSP satellite, suggest that the MF bursts are generated by electrons with an average energy of several keV associated with auroral breakup. On the other hand, the auroral roar is generated as upper hybrid waves by relatively low-energy electrons over the observation site and propagates downward, being converted into L-O mode electromagnetic waves.

第6回極域科学シンポジウム[OS] 宙空圏11月16日（月） 国立極地研究所１階交流アトリウム

第6回極域科学シンポジウム[OS] 宙空圏11月16日（月） 国立極地研究所１階交流アトリウム

Published version also available at href=http://dx.doi.org/10.1186/s40623-015-0350-8 We present three eastward-expanding auroral surge (EEAS) events that were observed intermittently at intervals of about 15 min in the post-midnight sector (01:55–02:40 MLT) by all-sky imagers and magnetometers in northern Europe. It was deduced that each surge occurred just after each onset of a multiple-onset substorm, which was small-scale and did not clearly expand westward, because they were observed almost simultaneously with Pi 2 pulsations at the magnetic equator and magnetic bay variations at middle-to-high latitudes associated with the DP-1 current system. The EEASs showed similar properties to omega bands or torches reported in previous studies, such as recurrence intervals of about 15 min, concurrence with magnetic pulsations with amplitudes of several tens of nanotesla, horizontal scales of 300–400 km, and occurrence of a pulsating aurora in a diffuse aurora after the passage of the EEASs. Furthermore, the EEASs showed similar temporal evolution to the omega bands, during which eastward-propagating auroral streamers occurred simultaneously in the poleward region, followed by the formation of north-south-aligned auroras, which eventually connected with the EEASs. Thus, we speculate that EEASs may be related to the generation process of omega bands. On the other hand, the EEASs we observed had several properties that were different from those of omega bands, such as greater eastward propagation speed (3–4 km/s), shorter associated magnetic pulsation periods (4–6 min), and a different ionospheric equivalent current direction. The fast eastward propagation speed of the EEASs is consistent with the speed of eastward expansion fronts of the substorm current wedge reported in previous studies. The difference in the ionospheric current between the EEASs and omega bands may be caused by a large temporal variation of the surge structure, compared with the more stable wavy structure of omega bands.

We developed a computer simulation scheme for the motion of energetic particles trapped in the Earth's magnetic field during a magnetic storm. The particles are injected into the inner magnetosphere from the near-Earth plasma sheet by a strong inductive electric field due to a dipolarization in association with a substorm. The motion of the particles is traced by the bounce-average approximation under a dipolar magnetic field and the Volland-Stern type convection field. The absolute quantity of a directional differential flux of the particles can be obtained. We can calculate the azimuthal component of the current density and an H-component of the magnetic disturbance at the center of the Earth (Dst^*) induced by the current. In this paper, we examine the formation of the ring current and the magnetic disturbance on the moderate storm occurred on February 13-14,1972. We find that (1) the inductive electric field due to the dipolarization may be one of major contributors to Dst^* on this storm, (2) the steep variations of Dst^* in the main phase cannot reproduced by the inductive electric field model, (3) the intensity of Dst^* is sensitive to the number density in the near-Earth plasma sheet, that is, an enhancement of the number density in the near-Earth plasma sheet may produce the steep and the major variations of Dst^*.

Using the auroral boundary index derived from DMSP electron precipitation data and the Dst index, changes in the size of the auroral belt during magnetic storms are studied. It is found that the equatorward boundary of the belt at midnight expands equatorward, reaching its lowest latitude about one hour before Dst peaks. This time lag depends very little on storm intensity. It is also shown that during magnetic storms, the energy of the ring current quantified with Dst increases in proportion to Le–3, where Le is the L-value corresponding to the equatorward boundary of the auroral belt designated by the auroral boundary index. This means that the ring current energy is proportional to the ion energy obtained from the earthward shift of the plasma sheet under the conservation of the first adiabatic invariant. The ring current energy is also proportional to Emag, the total magnetic field energy contained in the spherical shell bounded by Le and Leq, where Leq corresponds to the quiet-time location of the auroral precipitation boundary. The ratio of the ring current energy ER to the dipole energy Emag is typically 10%. The ring current leads to magnetosphere inflation as a result of an increase in the equivalent dipole moment.Key words. Ionosphere (Auroral ionosphere) · Magnetospheric physics (Auroral phenomena; storms and substorms)

Auroral tomography is a state-of-the-art method to retrieve three dimensional (3D) structure of luminous aurora from images taken simultaneously at multiple observation points. Imaging is basically monochromatic and altitude structures as well as horizontal vortex structures at particular wavelength are reconstructed. These are crucial for quantitative understanding of auroral formation and dynamical processes. In March 1995,the first multi-point international campaign between Sweden and Japan was carried out using three unmanned Swedish ALIS stations (Kiruna, Merasjarvi, Tjautjas) and two Japanese sites (Abisko, Nikkaluokta), separated by about 50km in Kiruna region. ALIS stands for the Auroral Large Imaging System which aims at capturing large-scale composite auroral images as well as optical tomographic imaging by a computer-controlled networking. In this paper, a description is given on the analysis of auroral tomography on the reconstruction of folded auroral arc observed at 2340 : 30 UT on March 26,1995. The images are taken for 1-5s integration at a green line of 557.7nm. Cameras were pointed to one of the preset common field of view, viz., a core region which is just overhead of Kiruna. Optical tomography relying on inversion analysis by the algebraic reconstruction technique has been carried out. The result indicates a fold structure of auroral arc with inferred altitude profile of photo-emission peaking at around 120km.

The Monte Carlo method was applied to investigate electron auroras observed by the sounding rocket S-310JA-8,which was launched on April 4,1984 from Syowa Station in Antarctica of the invariant latitude 66.14°S and the geomagnetic longitude 70.98°. The number density of the atmosphere, in which constituent elements were assumed to be N_2,O and O_2,and temperatures were estimated by the MSIS-86 model for the aurora observed there. A downward electron differential number flux was measured at the altitude of 200km, from which electrons were injected downward into the upper atmosphere. An initial electron energy E_0 is investigated in the range from 100 eV to 18 keV. An initial pitch angle was assumed to be uniformly distributed in the range of [0,π/2].Ionization rates of N_2,O and O_2 were calculated as a function of an altitude, the initial pitch angle, and the initial electron energy. The total ionization rate obtained by summing up individual ionization rate was considered to be a production rate of thermal electrons. A loss rate of thermal electrons was estimated by using an electron density and an effective recombination rate. Under the assumption of local equilibrium of ionization and recombination, the height profile of electron density was deduced and compared with the observed one. The height profile of an emission rate was also investigated for the oxygen green line. The emission rate calculated as contribution from the electron impact was compared with the one produced by the collision process N_2 (A^3Σ_u^+)+O(^3P), and it was made clear that the latter collision process was more efficient to excite oxygen atoms from O(^3P) to O(^1S) than the electron impact in the wide range of electron energy observed by the sounding rocket.

Electron auroras observed by the sounding rocket S-310JA-8 are investigated by using the Monte Carlo method. The MSIS-86 model is employed to represent the atmospheric number density and temperature in the aurora observed at Syowa Station in Antarctica of the invariant latitude 66.14°S and the geomagnetic longitude 70.98°on April 4,1984. Only N_2,O and O_2 are taken into account as components of the atmosphere. Electrons are injected downward into the upper atmosphere at the altitude of 200km, at which a downward electron differential number flux was measured. An initial electron energy E_0 is considered in the range of 100eV to 18keV. It is assumed that an initial pitch angle is uniformly distributed in the range of [0,π/2]. Production and emission at λ427.8nm rates of the first negative band system of nitrogen molecular ions N^+_2 (B^2Σ^+_u) are calculated as a function of altitude, the initial pitch angle, and the initial electron energy. Time variation of the observed absolute intensity of this line is reasonably well reproduced by the Monte Carlo method combined with the measured electron number flux. The difference in the absolute intensities obtained by experiment and theory is 5% at the time X+216s. This confirms that the Monte Carlo method is applicable to simulate collision processes and the resulting production and emission rates in electron auroras. Some representative results of emission rates are also presented for oxygen green and red lines.

Development of the ring current is one of major phenomena during a magnetic storm in the Earth's magnetosphere. Ring current protons collide with other particles (e.g., geocoronal hydrogen and plasmaspheric electrons) and lose their energies within a few days. The primary loss processes for ring current protons are considered as; (i) charge exchange with the geocoronal neutral hydrogen, and (ii) Coulomb collision with the plasmaspheric thermal electrons. In order to estimate the loss rate caused by both loss processes numerically, it is essential to trace each particle along their trajectories because the drift paths basically depend on energy, pitch angle, initial position of charged particles and the magnetospheric electric and magnetic fields. For this purpose, we have developed a particle simulation code including the charge exchange and the Coulomb collision as the major loss processes with a time-dependent magnetospheric electric field. A new plasmaspheric density model is also developed to evaluate the Coulomb collision between the ring current protons and the plasmaspheric thermal electrons. This model is a two dimensional and time-development on plasmaspheric number density, derived from a continuity equation along a magnetic flux tube connecting with the conjugate ionospheres in both hemispheres. Using this model, we obtained the electron density distribution in the plasmasphere which was fairly consistent with the one obtained by EXOS-B satellite observation. In this paper, we demonstrate the trajectory of 100 eV (lower energy) and 100keV (higher energy) protons associated with a magnetic storm. Their energies are lost effectively by Coulomb collisions more than charge exchange loss process, and hence, thermal electron distribution in the inner plasmasphere gives an important effect for lower and/or higher energy protons.

Image Database Systems usually have some keywords selected by human decision. In recent years, it has been an interesting problem to develop a method by which shapes, colors and contents for a specific image from image files are recognized automatically through image processing. Furthermore, it becomes important to determine properly the keywords representing impression of images, that is, 'KANSEI' words. We try to construct a database and data search system of the DMSP satellite auroral image files. At first, an index file including information such as file name, size, date and geometric feature of images is created through image processing. The impressional items for auroral shapes such as brightness, position, and impression are derived by a coordinate conversion method so called the 'KANSEI' space method. The system contains about 100 image files and the index file. A specific image data is searched with the index file and the conversion method of 'KANSEI' words.

(New) Dome Fuji Station, which is located at 3800m above sea level and whose temperature is quite low (-20℃～-80℃), is one of the best and unique sites for astronomical observations at infrared to submillimeter wavelengths on the ground. We are planning to constract two large terahertz and infrared telescopes at the station under the 9th JARE six-year plan, aiming at making astronomical observations including to search missing galaxies., 第4回極域科学シンポジウム特別セッション：[S] 南極研究の将来展望―第Ⅸ期6か年計画策定に向けて11月14日（木） 国立極地研究所 ２階大会議室

Energetic protons in the radiation belt of the earth's magnetosphere show energy density enhancement associated with geomagnetic storms/substorms, which observation with Explorer 45 evidently revealed as a nose structure in the E-t spectrogram inside the plasmasphere. An attempt has been made to explain this by an injection model in which energetic protons are injected around a nightside geosynchronous orbit with their subsequent inward motions due to a convection electric field possibly driven by the solar wind and a corotation electric field. It is also important to include a loss mechanism in the model inside the plasmasphere since the protons decay due to charge exchange loss processes with geocoronal neutral hydrogen. The loss rate of protons depends on the hydrogen density and charge exchange cross section. In this study, the effect of the charge exchange loss is examined by computer simulation of energetic proton trajectories in the magnetosphere; the hydrogen density being obtained by the Chamberlain model and the charge exchange cross section being adopted from the latest approximate formula. It is concluded that loss processes play an essential role in the energy density distributions of protons in the near earth radiation belts, especially inside L of about 4.

第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月16日（水） 統計数理研究所 セミナー室2

第2回極域科学シンポジウム/第35回極域宙空圏シンポジウム 11月15日（火） 国立極地研究所 2階大会議室

Simultaneous observations of auroral kilometric radiation from the Northern and Southern Hemispheres showed some cases in which the buildup of field-aligned acceleration occurred only in one hemisphere at the substorm onset. This indicates that a substorm does not always complete the current system by connecting the cross-tail current with both northern and southern ionospheric currents. Conjugate auroral observations showed that in one case, the auroral breakup in the Northern and Southern Hemispheres was not simultaneous; rather, they occurred a few minutes apart. This time difference in the breakup between two hemispheres suggests that the local auroral ionosphere controls auroral breakup in each hemisphere independently. The evidence in this study may indicate that the buildup of the field-aligned acceleration region at the auroral breakup does not result only from the magnetospheric process and that the auroral ionosphere finally controls and/or ignites the substorm onset, that is, the auroral breakup.

[1] We have investigated characteristics of ion upflow and naturally enhanced ion-acoustic lines (NEIALs) based on the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) data continuously obtained between March 2007 and February 2008. For the ion upflow study we have used approximately 78,000 field-aligned profiles obtained with the ESR. For the NEIAL study we have identified approximately 1500 NEIALs in the ESR data at altitudes between 100 and 500 km. The occurrence frequency of ion upflow shows two peaks, at about 0800 and 1300 magnetic local time (MLT), while only one strong peak is seen around 0900 MLT for NEIALs. The upward ion flux also has only one peak around 1100–1300 MLT. The occurrence frequency of ion upflow varies strongly over season. It is higher in winter than in summer, whereas NEIALs are more frequent in summer than in winter. NEIALs frequently occur under high geomagnetic activity and also high solar activity conditions. Approximately 10% of NEIALs in the F region ionosphere were accompanied by NEIALs in the E region (occurred at altitudes below 200 km). About half of the E region enhanced echoes did not have an F region counterpart. Upshifted NEIALs dominate in the E region whereas downshifted NEIALs are usually stronger above an altitude of 300 km. The high occurrence frequency of NEIALs in the prenoon region (0800–1000 MLT) might be associated with acceleration of thermal ions to suprathermal ones. At the same MLT and geomagnetic latitude suprathermal ions and broadband extremely low frequency (BBELF) wave activity have been observed, according to previous studies.