ブロックオヨビコウゴキョウジュウゴウタイノコウゾウトブッセイノカンレンセイニカンスルケンキュウ

京都大学0048新制・論文博士工学博士乙第1980号論工博第497号新制||工||218(附属図書館)3026UT51-47-B497(主査)教授 古川 淳二, 教授 河合 弘廸, 教授 小野木 重治学位規則第5条第2項該当Kyoto UniversityDA

Complementing regional ground GNSS-STEC computerized ionospheric tomography (CIT) with ionosonde data assimilation

A near-real-time computerized ionospheric tomography (CIT) technique was developed over the East Asian sector to specify the 3-D electron density field. The technique is based on a plethora of Global Navigation Satellite System observables within the region of interest which is bounded horizontally 110°–160°E and 10°–60°N and extending from 80 to 25, 000 km in altitude. Prior to deployment, studies validated the CIT results using ionosonde, middle-upper atmosphere radar and occultation data and found the technique to adequately reconstruct the regional ionosphere vertical structure. However, with room for improvement in estimating the peak height and avoiding physically unrealistic negative densities in the final solution, we present preliminary results from a technique that addresses these issues by incorporating CIT results into a data assimilation (DA) technique. The DA technique adds ionosonde bottomside measurements into CIT results, thereby improving the accuracy of the reconstructed bottomside 3-D structure. More specifically, on average CIT NmF2 and hmF2 improve by more than 60%. Further, during analysis, ionospheric electron densities are assumed to be better described by probability log-normal distribution, which introduces the positivity constraint that is mandatory in ionospheric imaging

テイキドウ エイセイ ト チジョウ GPS ジュシンキモウ ノ TEC データ デ カンソク サレタ SED ノ コウド コウゾウ

低軌道衛星搭載GPS 受信機と地上GPS 受信機網の電離圏全電子数(Total Electron Content; TEC)データを用いて,地磁気擾じょうらん乱時に北半球電離圏において赤道異常帯から北西方向へ高電子密度領域が細長く伸びる現象,Storm-enhanced density(SED)の電子密度高度構造の解明を行った.本研究では北米大陸でSED が発生していた2 つの事例に対し,Gravity Recovery and Climate Experiment(GRACE)衛星搭載のGPS 受信機による高度500?20000 km のTEC データ(GRACE-TEC)と,地上-GPS 衛星間TEC データを用いて,SED の観測を行った.その結果,2 つのSED を観測し,GRACE-TEC データでは,地上-GPS 衛星間TEC データよりも3-5° 程度高い緯度でSED が観測されることが明らかになった.これは,SED の低緯度側では高度500 km以上にあるプラズマは高度500 km 以下にあるプラズマの? 程度であるが,SED の高緯度側では高度500 km 以上にあるプラズマは高度500 km 以下にあるプラズマの1.1-2.7 倍であり,SED 内部において,高緯度ほど高い高度にプラズマ密度が増加しているためである.このような緯度-高度構造は,SED 内部の増加した東向き電場によるE×B ドリフトによるものと解釈される.The altitudinal structure of Storm-enhanced density (SED) was studied using the Total Electron Content (TEC) data of the GPS receiver on the Gravity Recovery and Climate Experiment (GRACE) satellite and the ground-based GPS receivers. The GRACETEC-data are derived from the GPS receiver on the GRACE satellite. A SED is a high-electron density phenomenon that extends from the Equatorial Ionization Anomaly (EIA) toward the north-west in the northern hemisphere during geomagnetic disturbed time. TwoSEDs were observed as TEC variations in the GRACE-TEC data and in the ground-GPS TEC data. The ground-GPS TEC data is the TEC data between the ground GPS receiver and the GPS satellites. The SED observed in the GRACE-TEC data appeared at higher latitudes than that in the ground-GPS TEC data. We concluded detected that the altitudinal structure of the SED would be different between at lower than at higher latitudes due to the effects of the eastward E×B drift

Temporal change of EIA asymmetry revealed by a beacon receiver network in Southeast Asia

To reveal the temporal change of the equatorial ionization anomaly (EIA) asymmetry, a multipoint satellite-ground beacon experiment was conducted along the meridional plane of the Thailand–Indonesia sector. The observation includes one station near the magnetic equator and four stations at off-equator latitudes. This is the first EIA asymmetry study with high spatial resolution using GNU Radio Beacon Receiver (GRBR) observations in Southeast Asia. GRBR-total electron contents (TECs) from 97 polar-orbit satellite passes in March 2012 were analyzed in this study. Successive passes captured rapid evolution of EIA asymmetry, especially during geomagnetic disturbances. The penetrating electric fields that occur during geomagnetic disturbed days are not the cause of the asymmetry. Instead, high background TEC associated with an intense electric field empowers the neutral wind to produce severe asymmetry of the EIA. Such rapid evolution of EIA asymmetry was not seen during nighttime, when meridional wind mainly controlled the asymmetric structures. Additional data are necessary to identify the source of the variations, i.e., atmospheric waves. Precisely capturing the locations of the crests and the evolution of the asymmetry enhances understanding of the temporal change of EIA asymmetry at the local scale and leads to a future local modeling for TEC prediction in Southeast Asia

Analysis of the altitudinal structure of Storm-enhanced density using Total Electron Content data of space-borne and ground-based GPS receivers

The altitudinal structure of Storm-enhanced density (SED) was studied using the Total Electron Content (TEC) data of the GPS receiver on the Gravity Recovery and Climate Experiment (GRACE) satellite and the ground-based GPS receivers. The GRACETEC-data are derived from the GPS receiver on the GRACE satellite. A SED is a high-electron density phenomenon that extends from the Equatorial Ionization Anomaly (EIA) toward the north-west in the northern hemisphere during geomagnetic disturbed time. TwoSEDs were observed as TEC variations in the GRACE-TEC data and in the ground-GPS TEC data. The ground-GPS TEC data is the TEC data between the ground GPS receiver and the GPS satellites. The SED observed in the GRACE-TEC data appeared at higher latitudes than that in the ground-GPS TEC data. We concluded detected that the altitudinal structure of the SED would be different between at lower than at higher latitudes due to the effects of the eastward E×B drift