Ground-based observation and full-wave analysis of the ionospheric VLF propagation around the earth / 地上観測とfull-wave解析による地球周辺自然VLF波動の電離層伝搬に関する研究

取得学位：博士(工学)，学位授与番号：博甲第1075号，学位授与年月日：平成21年3月23

Reduction of multiple narrow-band noises from radio waves

This paper proposes reduction of mul- tiple narrow-band noise signals from radio signals. The multiple narrow-band noise signals are suppressed one- by-one basis by using sinusoidal signal generators and an adaptive filter. The frequencies are estimated from the amplitude spectrum. Based on the histogram of fre- quency differences, low-power harmonic components can be detected. Fine tuning on frequency is carried out by using the averaged power pattern of three narrow-band- filter outputs. Peak filters are introduced in order to sup- press influence of wide-band signals. The performance are examined by using real measured signals

Characteristics of energetic electron precipitation associated with chorus emissions and pulsating aurora observed at Syowa Station: A case study on 17 May 2007

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26日（月）、27日（火） 国立極地研究所 2階ラウン

Small sensor probe for measuring plasma waves in space Space science

Background: Since conventional one-point observations of plasma phenomena in space cannot distinguish between time and spatial variations, the missions on the basis of multiple-point observations have become the trend. We propose a new system for multiple-point observation referred to as the monitor system for space electromagnetic environments (MSEE). Findings: The MSEE consists of small sensor probes that have a capability to measure electromagnetic waves and transfer received data to the central station through wireless communication. We developed the prototype model of the MSEE sensor probe. The sensor probe includes a plasma wave receiver, the microcontroller, the wireless communication module, and the battery in the 75-mm cubic housing. In addition, loop antennas, dipole antennas, and actuators that are used for expanding dipole antennas are attached on the housing. The whole mass of the sensor probe is 692 g, and the total power consumption is 462 mW. The sensor probe can work with both inner battery and external power supply. The maximum continuous operation time on battery power is more than 6 h. We verified the total performance for electric field measurements by inputting signal to preamplifier. In this test, we found that analog components had enough characteristics to measure electric fields, and the A/D conversion and the wireless transmission worked correctly. In the whole performance for electric fields, the sensor probe has equivalent noise level of - 135 dBV/m/√Hz. Conclusions: We succeed in developing the prototype model of the small sensor probe that had enough sensitivity for electric field to measure plasma waves and the ability to transfer observation data through wireless communication. The success in developing the small sensor probe for the measurement of plasma waves leads to the realization of the multiple-point observations using a lot of small probes scattered in space

シゼン VLF ホウシャ キョウド ト ギンガ ザツオン デンパ キュウシュウ CNA ノ ソウカン カンケイ ヲ モチイタ カブ デンリソウ デンシ ミツド ノ スイテイ

本研究では,地上で観測されるVLFホイスラモード波(昼間に観測されるコーラス)の電離層減衰率とCNAを用いた新しい下部電離層電子密度のリモートセンシング技術を提案する.そのために,さまざまな電子密度モデルに対する両者の関係を理論的に評価している.評価の手法は,full-wave解析を用いてVLFホイスラモード波の下部電離層減衰率とCNAを理論計算している.計算結果は観測結果と同様にCNAとVLF波動の負相関を示し,さらに,増大した電子密度モデルの最大電子密度高度が下がるにつれ,CNA-VLF負相関の傾きが増大する関係を示した.つまり,観測されたCNA-VLF負相関の傾きが,降下粒子に伴う下部電離層を増大させる電子密度高度を推定する情報源に成りえるということが分かった.これは,夜間のみに生じるTrimpi現象と共に,昼間の降下粒子検出に対する新しい下部電離層電子密度推定手法となるであろう.In this study, we suggest a new remote sensing technique for enhanced electron density in the lower ionosphere by using the correlation between VLF whistler mode waves (daytime chorus emissions) and CNA, both observed on the ground. The ionospheric attenuations for VLF whistler mode and HF waves (as a CNA value) are calculated by using full-wave analysis to evaluate their correlations for various ionospheric electron density profiles enhanced by precipitating electrons. The calculation results show negative correlations between CNA and VLF whistler mode waves in accordance with the observation results. Then, the gradient of the negative correlation becomes larger with decreasing altitude of maximum electron density. Thus, we found that the correlation provides information on the vertical profile of the enhanced electron density in the lower ionosphere caused by electron precipitation. This allows the study of electron precipitation in the daytime, in addition to Trimpi events at nighttime

Spatial Evolution of Wave‐Particle Interaction Region Deduced From Flash‐Type Auroras and Chorus‐Ray Tracing

In-situ observations of spatial variations of the wave-particle interaction region require a large number of satellite probes. As an alternative, flash-type auroras, a kind of pulsating aurora, driven by discrete chorus elements, can be used to investigate the interaction region with a high spatial resolution. We estimated the spatial extent of wave-particle interaction region from ground-based observations of flash aurora at Gakona (62.39°N, 214.78°E), Alaska at subauroral latitudes, and found that the auroral expansion was predominantly to the low-latitude side. The spatial displacement is thought to be caused by the propagation effects of chorus waves in the magnetosphere. Using ray tracing analysis to take into account chorus wave propagation, we reconstructed the spatiotemporal evolution of the volume emission rate and confirmed that the predominant expansion is toward the lower-latitude side in the ionosphere. This study shows that chorus wave propagation in the magnetosphere gives new insight for characterizing the transverse size (across the geomagnetic field line) of wave-particle interaction regions. The calculated spatial scale of the column auroral emission shows a correlation with the magnetic latitude of the resonance region at magnetic latitudes within 10° of the equatorial plane of the magnetosphere. Our results suggest that the spatial scale of a flash aurora is indirectly related to the chorus amplitude because the latitudinal range of the wave-particle interaction is important for the growth of wave amplitude

Magnetic Conjugacy of Pc1 Waves and Isolated Proton Precipitation at Subauroral Latitudes: Importance of Ionosphere as Intensity Modulation Region

Pc1 geomagnetic pulsations, equivalent to electromagnetic ion cyclotron waves in the magnetosphere, display a specific amplitude modulation, though the region of the modulation remains an open issue. To classify whether the amplitude modulation has a magnetospheric or ionospheric origin, an isolated proton aurora (IPA), which is a proxy of Pc1 wave-particle interactions, is compared with the associated Pc1 waves for a geomagnetic conjugate pair, Halley Research Base in Antarctica and Nain in Canada. The temporal variation of an IPA shows a higher correlation coefficient (0.88) with Pc1 waves in the same hemisphere than that in the opposite hemisphere. This conjugate observation reveals that the classic cyclotron resonance is insufficient to determine the amplitude modulation. We suggest that direct wave radiation from the ionospheric current by IPA should also contribute to the amplitude modulation

マッショウ タンカクキュウ サイボウ オ モチイタ マッショウ ドウミャク ヘイソクショウ ニ タイスル アラタナ ケッカン シンセイ リョウホウ ノ ココロミ

Earlier studies have shown that bone marrow-derived mononuclear cell（BM-MNC）implantation induces therapeutic angiogenesis in patients with peripheral arterial disease（PAD）. However, the invasiveness of bone marrow collection limits clinical application of BM-MNC implantation.We performed peripheral blood-derived mononuclear cell（PB-MNC）implantation in ischemic limbs of five patients with PAD. After implantation, clinical symptoms such as rest pain and numbness were relieved in four patients. Maximal walking distance markedly increased from 160 m to 915 m in one patient. Non-healing ulcers were cured after repeated cell implantation in one patient with Burger disease. There was no adverse event. These findings suggest that PB-MNC implantation is a safe and noninvasive strategy for therapeutic angiogenesis for the treatment of severe PAD

Spectral riometer observation of atmospheric iononization due to energetic electron precipitation

The Tenth Symposium on Polar Science/Special session: [S] Future plan of Antarctic research: Towards phase X of the Japanese Antarctic Research Project (2022-2028) and beyond, Tue. 3 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research (NIPR