ELF Emissions in High Latitudes-Ray Path Calculation and Ground-Satellite Observations

This paper deals with ELF emissions observed in the dayside magnetosphere, called ELF hiss and polar chorus. These waves are generated in the magnetic equatorial region through Doppler-shifted cyclotron wave-particle interaction by high- energy electrons. According to the satellite observations, the features of ELF emissions such as power spectrum and wave normal direction in low-altitude polar region are significantly different from magnetic equatorial plane after their propagation in the magnetosphere. Especially in ELF range, magnetospheric ions play a fundamental role in low-altitude propagation, for example in LHR reflection and multi-ion cutoff. Previous work on ELF wave ray tracing from the high-altitude magnetic equatorial plane to low altitudes revealed that most of the rays undergo LHR reflection before they reach the usual level of polar orbiting satellites. So, it seems that ELF emissions observed by polar orbiting satellites and on the ground have propagated along field-aligned ducts. However, there is abundant evidence from satellite ELF wave observations that the wave normal of ELF emission makes a large angle with the earth\u27s magnetic field at low altitudes, and this feature can be explained only by nonducted propagation. Therefore, it is important to find out the condition required for the nonducted ray path between the magnetic equatorial plane and low altitudes without suffering from LHR reflection. This kind of ray path is of special interest in the present study, and it is referred to as "penetrating ray path" in this paper. This paper is devoted to the study of the above two kinds of propagation from the magnetic equatorial plane to the polar region with the observations of ELF/VLF waves by ISIS satellites over Antarctica, ELF waves at Syowa Sation, Antarctica and Bremsstrahlung X-rays by balloons. Characteristics of ELF emissions observed at the high-altitude equatorial region and the low-altitude polar region are briefly reviewed first. Conditions for the existence of penetrating ray paths are obtained from a 2-dimensional ray tracing. Wave normal directions and arriving latitudes at low altitudes are also calculated. These calculated characteristics of ELF wave normals are compared with those from ISIS satellite observation in the altitude range of 1450-3500 km by means of spin-modulated characteristics and multi-ion cutoff characteristics of received ELF signals. Seasonal variation of ELF emission intensity at the ISIS satellite altitude and on the ground is attributable to a north-south asymmetry in the penetrating ray paths depending on a field-aligned electron density gradient in the both hemispheres. Another mode of ELF wave propagation, i.e., ducted propagation outside the plasmapause, is investigated for periodic emissions. This type of emission is recorded on the ground at regular intervals of several seconds, alternately in the opposite hemispheres. Hence the emission is thought to be caused by an echoing of wave packet between the two hemispheres along a field-aligned duct. Periodic emissions with the same repetition interval are often observed over an area of more than 2000 km wide at the ISIS satellite altitude and on the ground. Such a wide spatial extent of emission reception is explained in this chapter from a viewpoint that the ELF duct terminates at a certain altitude, below which the waves propagate downward widely in nonducted mode. Finally, ELF emissions observed on the ground are compared with Bremsstrahlung X-rays observed by balloons. As the electrons producing such X-rays precipitate along magnetic field lines, a pattern of electron precipitation observed on the ground is a projection onto the polar ionosphere of the wave-particle interaction region near the magnetic equator. Hence the electron precipitation associated with ELF emission activity affords useful information on the source location of ELF emissions. With this background in mind, three balloon experiments were carri

ダイ45ジ ナンキョク チイキ カンソクタイ エットウ ホウコク 2004-2005 -ショウワキチ オヨビ エンガン チイキ ノ カツドウ-

第45次南極地域観測隊越冬隊(45次越冬隊)は,隊員及び同行者42名が昭和基地で越冬し,第期5ヵ年計画の3年次にあたる定常観測,モニタリング研究観測を継続して行うと共に,宙空系,気水圏系,地学系,生物・医学系のプロジェクト研究観測を昭和基地とドームふじ観測拠点において実施した.また,設営関係では基地の運営を2004年2月1日から2005年1月31日まで担当し,電力, 上下水道,燃料,通信,食料,医療といった生活基盤の維持管理に加え,車両整備, 機械設備工事,航空機の運用ならびに滑走路のメンテナンス,LANの運用,野外観測支援など多くの作業を行った.またインテルサット衛星通信設備を建設し,本格的なデータ通信,インターネット,テレビ会議など多様な情報サービスの初年度の運用を行ったことは特記すべきである.昭和基地,及びオングル海峡の海氷が安定しなかったため,野外行動の本格的開始は極夜が明けた7月となった.8月以降,生物学,地球物理,大気観測に関する多くのリュツォ・ホルム湾沿岸調査旅行や航空機観測を実施した.45次越冬隊では朝日新聞記者2名が観測隊同行者として越冬し,南極の自然や隊の活動の報道を国内に送った.The 45th Japanese Antarctic Research Expedition (JARE-45) wintering party, consisting of 40 members and 2 journalists, conducted the third year program of the VIth five-year plan of JARE at Syowa Station and inland Dome Fuji Station. The program included observations in meteorology, upper atmosphere physics, atmospheric sciences, glaciology, geophysics, biology and medical science, as well as logistic activities to support the observations and maintain the station from February 1, 2004 to January 31, 2005. An Intersat satellite station was installed at Syowa Station in this expedition and started various sevices such as data transfer, internet and TV conference system. Due to the unstable sea ice condition around Syowa Station and Ongul Strait, the start of the field activities on sea ice was delayed until early July. However, many teams were engaged in field work in biology, geophysics and atmospheric sciences in the coastal area of east Lutzow-Holm Bay, as well as aeroplane observations. Two journalists at Syowa Station reported on the nature of Antarctica and various activities of the expedition

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

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

Lysophosphatidic acid signaling regulates the KLF9-PPAR gamma axis in human induced pluripotent stem cell-derived neurons

Lysophosphatidic acid (LPA) is a lipid signaling molecule that plays several significant roles in the nervous system during development and injury. In this study, we differentiated human induced pluripotent stem cells (iPSCs) into neurons as an in vitro model to examine the specific effects of LPA. We demonstrated that LPA activates peroxisome proliferator-activated receptor gamma (PPAR gamma), a ligand-activated nuclear receptor, as well as its cognate receptor LPA(1) on human iPSC-derived neurons to enhance proliferation and neurite outgrowth. Furthermore, we found that the gene expression of Kruppel-like factor 9 (KLF9), a member of the large KLF transcription factor family, was induced by LPA treatment. Knockdown of KLF9 decreased proliferation and neurite outgrowth in vehicle- and LPA-treated IPSC-derived neurons compared to cells expressing KLF9. In conclusion, LPA plays dual roles as a ligand mediator through the activation of cell surface G-coupled protein receptors and as an intracellular second messenger through the activation of PPAR gamma. We discuss the contribution of the LPA(1)-PPAR(gamma)-KLF9 axis to neurite outgrowth and proliferation in human iPSC-derived neurons. (C) 2017 Elsevier Inc. All rights reserved.ArticleBIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS. 491(1):223-227 (2017)journal articl

A new method for monitoring and removing SuperDARN radar DC offsets

DC offsets in quadrature outputs (I/Q signals) pertinent to the SuperDARN HF radars can cause problems in determining and analysing auto-correlation functions, cross-correlation functions and raw time series data if they are not negligible. We have developed a new code to monitor and remove DC offsets. To obtain correct DC offset levels and noise levels, the offsets can be best removed using I/Q signals during the receive-only period, i.e., during each clear frequency search stage. We have implemented the new code in the current radar operating system, installed it at the SENSU Syowa radars, and have been obtaining and removing DC offset values continuously since October 2001

Characteristics of Pc5 pulsations deduced from antarctic geomagnetic observations during the Relativistic Electron Enhancement (REE) events at the Outer Radiation Belt

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月27日（火） 国立極地研究所 2階大会議

Implications of statistics of near-range Doppler velocity observed with the Syowa East HF radar

A large data-set of line-of-sight Doppler velocity obtained with the Antarctic Syowa East HF radar from February to December 1997 is analyzed to discuss the statistical characteristics of Doppler velocity (V_D) at ranges of 180-1200 km and their implications. Syowa Station K-indices during the observation period were between 0 and 7 with a maximum occurrence at K = 1. On average V_D has a minimum of about 100 m/s at 180-225 km ranges. With increasing range it increases monotonically to attain a maximum of 300-350 m/s at 400-500 km, decreases gradually to reach 250-300 m/s at about 700km, and again increases slowly at farther ranges. These values of V_D and the range vary depending on both local time and radar beam direction. In the light of recent knowledge of plasma instabilities in the ionosphere we suggest that such range profile of V_D is mainly caused by the combined effects of altitude-dependent phase velocities of ionospheric plasma waves, HF wave refraction due to enhanced E region electron density, and latitude-dependent electric field. We infer that the low V_D (～ 100 m/s) at ranges of 180-225 km may originate in part from neutral winds and/or turbulence of the neutral atmosphere