Extremely periodic pulsating aurora observed near L=6: A new type pulsating aurora

Extremely periodic pulsating aurora, a new type pulsating aurora, was detected by three photometers (directing towards the zenith and 45° N and S in the meridian plane, for 427.8 nm emission) at Husafell in Iceland on 18-19 December 1985. We examined the characteristics of the pulsating auroras and their relationship to magnetic pulsations using the data obtained in Iceland and Syowa Station, the geomagnetically conjugate pair station in Antarctica. The characteristics of this event are as follows; 1) extremely regular periodic pulsating auroras with the frequency of -50 mHz were observed simultaneously on the 3 photometers, 2) the periodicity of the pulsation was extremely high, and the Q-value showed more than 20, 3) the intensity variation among the 3 photometers occurred with excellent coherency and simultaneously without time lag, suggesting that these pulsating auroras were not of a propagating type but a standing type, 4) there are no correlation between the optical pulsating auroras and magnetic pulsations on the ground. These characteristics suggest that the extremely periodic pulsating aurora on this event is not a common (popular) pulsating aurora but an exceptional type pulsating aurora which would occur under a certain condition in the magnetosphere

Quasi-Periodic (QP) ELF-VLF Emissions Observed in High Latitudes

The characteristics of quasi-periodic (QP) ELF-VLF emissions with periods of 3-150 s and their relationships to magnetic pulsations are studied by using data obtained from Syowa and Mizuho Stations in Antarctica and Husafell in Iceland which is located near the geomagnetic conjugate point of Syowa Station. From the relations of QP emissions to magnetic pulsations, QP emissions are classified into two types, Type 1 and 2 QP emissions, according to whether the emissions are clearly associated with magnetic pulsations or not. The typical characteristics of Type 1 QP emissions are as follows. The intensity and period of QP emissions change concurrently with variations in the intensity and period of magnetic pulsations. From the coherency analysis between QP emissions and Pc 3-4 magnetic pulsations it is found that the coherency between the D component of magnetic pulsations and the intensity fluctuations of QP emissions is much higher than that between the H component of magnetic pulsations and QPs. It is also found that the propagation time of magnetic pulsations (HM waves) from the interaction region between magnetic pulsations and QPs in the magnetosphere to the ground is 20-30 s. These properties are observed at conjugate-pair stations with good conjugacy. The results strongly suggest that Type 1 QP emissions are modulated by compressional mode Pc 3-4 magnetic pulsations near the equatorial plane in the outer magnetosphere. On the other hand, QP emissions are categorized as the Type 2 QP emissions when the period of concurrent pulsations is entirely different from that of QP emissions or the amplitude of pulsations is too small to determine the periodicity. The most striking feature of Type 2 QP emissions are their very regular periodicity as compared with that of Type 1 QP emissions, and the Q value of the spectral peak usually attains to more than 10. In most cases magnetic variations during Type 2 QP events, which occur under magnetically quiet condition, have no spectral peak corresponding to the peak in QP\u27s spectrum. However, a small but significant peak in pulsation spectrum is occasionally noted, when the Type 2 QP event occurs in modelate disturbed condition. The peak value of magnetic spectrum, in such a case, is generally two order of magnitude less than the maximum power of background magnetic fluctuations. The amplitude of magnetic pulsations is in the 2 QP ELF-VLF Emissions Observed in High Latitudes order of 0.001 nT/s. The H component of magnetic pulsations tends to be more correlated with the VLF intensity variations than that the D component. These properties are observed at conjugate-pair stations with good conjugacy. It is suggested that weak magnetic pulsations, correlated with the Type 2 QP, are produced by wave induced particle precipitations. As to the periodicity of Type 2 QP emissions, either the period is controlled by compressional magnetic waves which are usually not detected on the ground, or the period of QPs is controlled by some other modulation mechanism which is unknown at present. The frequency-time (f-t) spectra of QP emissions are classified into five types. A phenomenological model to explain the f-t spectra is proposed, that is, the rising-tone type of QP emission is generated by compressional mode Pc 3 magnetic pulsations which propagate in radial direction toward the earth, while the non-dispersive type is generated by standing oscillations of the magnetic field which have effective compressional components

Issues on understanding of pulsation aurora

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

New sounding modes for SuperDARN HF radars

We have developed several new sounding modes for SuperDARN HF radars to increase operation flexibility ("Nasu" mode, etc.) as well as to obtain both higher time resolution special camping beams data and global convection patterns simultaneously ("Basyouhu" mode). Utilizing the new "Basyouhu" mode, we were able to detect, for the first time, very rapidly moving transient phenomena (about 20 km/s) passing through the SuperDARN radar\u27s field of view without any ambiguity or uncertainty

Similarity and dissimilarity of conjugate relationships of Pi magnetic pulsations observed during excellent similar auroras

Similarity and dissimilarity of conjugate relationships of Pi magnetic pulsations observed during excellent similar auroras at the conjugate stations, Tjornes in Iceland and Syowa Station in Antarctica are examined. The study revealed that characteristic Pi pulsations, Pi 2 pulsations and impulsive Pi 1 pulsations were prominently observed with a close relationship to aurora activities. During the substorm growth phase they showed a good similarity between the conjugate stations. How ever, at the onset of substorm expansion, the appearance of Pi pulsations showed prominent dissimilarity between the conjugate stations, suggesting that there might be some asymmetry of the ionosphere and magnetosphere conditions in between the northern and the southern hemispheres

A cross-correlation analysis of Pi oscillations in auroral luminosity and magnetic field variations

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 2階 大会議

Cusp-latitude conjugate ionospheric absorption associated with increase of solar wind dynamic pressure during strong northward IMF-a case study

Conjugate ionospheric absorption was observed in the magnetic pre-noon by the inter-hemispheric imaging riometers (IRISs) at Ny-Alesund (NAL), Svalbard and Zhongshan (ZHS), Antarctica in the cusp-latitude. The absorption was associated with increase of solar wind dynamic pressure during the strong northward interplanetary magnetic field. The conjugate absorption features showed a sequence of spike-shape with intensity of 400 km) exceeding the IRIS field-of-view with a poleward motion. The absorption spikes at NAL preceded the ones at ZHS by about 4 min. The absorption at NAL was located at part of enhanced auroral luminosity in the main oval from the POLAR UVI images, and also near the lower-latitude convection reversal in the plasma convection cell from the SuperDARN radar network of the northern hemisphere. Conjugate relationships, electrodynamics of electron precipitation and possible absorption mechanisms are discussed from these characteristics