Temporal and spatial variations of the total electron content from the high-latitde to equatorial ionosphere during a geomagnetic storm on 27 and 28 September 2017

The Tenth Symposium on Polar Science/Ordinary sessions: [OS] Space and upper atmospheric sciences, Wed. 4 Dec. /Entrance Hall (1st floor) at National Institute of Polar Research (NIPR

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journal articl

GPS scintillation during storm-time substorms

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

Temporal and Spatial Variations of Total Electron Content Enhancements During a Geomagnetic Storm on 27 and 28 September 2017

Temporal and spatial evolutions of total electron content (TEC) and electron density in the ionosphere during a geomagnetic storm that occurred on 27 and 28 September 2017 have been investigated using global TEC data obtained from many Global Navigation Satellite System stations together with the ionosonde, geomagnetic field, Jicamarca incoherent scatter and Super Dual Auroral Radar Network (SuperDARN) radar data. Our analysis results show that a clear enhancement of the ratio of the TEC difference (rTEC) first occurs from noon to afternoon at high latitudes within 1 hr after a sudden increase and expansion of the high‐latitude convection and prompt penetration of the electric field to the equator associated with the southward excursion of the interplanetary magnetic field. Approximately 1–2 hr after the onset of the hmF2 increase in the midlatitude and low‐latitude regions associated with the high‐latitude convection enhancement, the rTEC and foF2 values begin to increase and the enhanced rTEC region expands to low latitudes within 1–2 hr. This signature suggests that the ionospheric plasmas in the F2 region move at a higher altitude due to local electric field drift, where the recombination rate is smaller, and that the electron density increases due to additional production at the lower altitude in the sunlit region. Later, another rTEC enhancement related to the equatorial ionization anomaly appears in the equatorial region approximately 1 hr after the prompt penetration of the electric field to the equator and expands to higher latitudes within 3–4 hr.ファイル公開：2021-01-01journal articl

イオノゾンデ オヨビ ファブリ・ペロー カンショウケイ ニ ヨッテ カンソク サレタ シゴメン ネツケンフウ ノ ヒカク

電離圏ダイナミクスに大きく寄与する熱圏風についての理解を深めるため,イオノゾンデの磁気共役点観測により推定された南北方向の熱圏風(推定熱圏風)と,ファブリ・ペロー干渉計(FPI)観測により直接測定された南北方向の熱圏風との相関を調べた.推定熱圏風は,磁気共役点における熱圏風は等しい(赤道横断風モードが卓越する)という仮定のもとで導出される.2 つの手法で観測された夜間の熱圏風を比較するのは本研究が初めてである.2010 年のチェンマイ(タイ)とコトタバン(インドネシア)のイオノゾンデとFPI データを比較した結果,両者はおおむね良い相関を示したが,相関が悪い日もあった.相関が悪い事例は,赤道から収束・発散する成分を無視できず,赤道横断風モードが卓越するという仮定が成立しないと解釈されるものである.また,2 つの手法で求めた熱圏風の相関を季節別に調べると,2-4 月に両者の相関が高い一方,5-7 月に両者の相関が低いことがわかった.To comprehend ionospheric-thermospheric coupling, one must understand the thermospheric wind system. However, measuring the thermospheric wind using a Fabry-Perot interferometer (FPI) is not an easy task. Because of this difficulty, some researchers have estimated meridional wind velocities using data obtained from a pair of ionosonde stations near the geomagnetic conjugate points, under the assumption that the meridional wind is the same at the two ionosonde stations (transequatorial mode wind). In this paper, we construct the first comparison of the estimated meridional wind velocitieswith meridional wind observed with FPIs. We analyzed data from the ionosondes and FPIs installed at Chiang Mai, Thailand, and Kototabang, Indonesia, from 2010. We found that the estimated and observed wind velocities were generally in good agreement on most nights, although on some nights, the wind velocities were different. The assumption that the meridional wind is equal anywhere between the two ionosonde stations would not be suitable for the days when the winds were not in good agreement. We also investigated the seasonal dependence of the correlation between the estimated and observed meridional winds. They were in good agreement from February to April and were not in good agreement from May to July

Northward-propagating nighttime medium-scale traveling ionospheric disturbances observed with SuperDARN Hokkaido HF radar and GEONET

We report on the characteristics of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) propagating northward observed with the SuperDARN Hokkaido HF radar, which has a field of view to the north of Japan, and occasionally with the GNSS Earth Observation NETwork (GEONET), which provides total electron content (TEC) data over Japan. From statistical analysis of MSTIDs observed with the Hokkaido radar during nighttime (1700–0700 LT) from January 2007 to July 2009, we find that these MSTIDs traveling northward, although rare in comparison with those traveling southwestward, have a relatively high occurrence rate after sunset and around midnight in May and August, which is partly consistent with the occurrence rate of MSTIDs over Japan observed with GEONET in 2002, when the MSTID event database is available. We also use the data from simultaneous observation of nightside MSTIDs by the Hokkaido radar and GEONET to find that when the HF radar observed northward-propagating MSTIDs, GEONET did not always observe such MSTIDs with the same propagation direction. Judging from this result and considering the HF radar field of view located to the north of the GEONET coverage area, we speculate that some physical parameters of the ionosphere/thermosphere over Japan differ from those to the north of Japan, which may result in the inconsistency of MSTID propagation direction. The present results provide new knowledge of MSTIDs propagating northward using the Hokkaido radar, whose field of view was not covered by GEONET

Equatorial Electrojet and electron density over Southeast Asian Region during moderate solar activity condition

125-131The study presents a simultaneous variation of equatorial electrojet (EEJ) current and the ionospheric F2-layer maximum electron density (NmF2) during geomagnetic quiet days and moderate solar conditions (solar radio flux, 10.7 120 sfu). The geomagnetic measurements at Kotatobang (KTB) and Langkawi (LKW) stations have been used to estimate the magnetic daily variation in H-component and in deriving EEJ. The NmF2 data set is from Frequency Modulation Continuous Wave (FM-CW), an analogue ionosonde located at the KTB station. The study examines both the diurnal and seasonal variation in EEJ and the corresponding effect on the measured NmF2. The results obtained show that the derived EEJ at LKW shows a daytime peak which coincides with the period NmF2 measurement at KTB station depleted to a daytime low value. The role of EEJ at the LKW station correlates poorly with the NmF2 at KTB in which their correlation coefficient (r) is in the range of 0.02 to 0.04 for equinox, summer and winter, respectively. However, an r-value of 0.33 was observed when the whole data set for the year 2012 was considered. The poor correlation coefficient between derived EEJ and NmF2 measured at KTB during the moderate solar condition suggest that EEJ has little or no influence on the prevailing ionospheric condition at a low latitude station located outside the EEJ strip