Seasonal dependence of semidiurnal equatorial magnetic variation during quiet and disturbed periods

The analysis of 20-year long-term semidiurnal lunar tidal variations gave the evidence that the semidiurnal variations are completely different between the magnetic quiet and disturbed periods. This is the first time that the seasonal dependence of disturbance-time semidiurnal variation has been provided from the analysis of the EE-index. We found the Kp dependence of semidiurnal variation: For full and new moon phase, counter troughs are amplified during disturbance time, possibly related to disturbance dynamo. For all moon phase, there are positive enhancements in dawn and strong depressions after sunset, resulting from the penetration of polar electric filed. For Seasonal dependence, semidiurnal variations are divided to three seasonal groups, and characterized as deep trough, enhanced crest and weak structure for D-solstice, Equinoxes and J-solstice, respectively. There is no significant longitudinal difference between Ancon and Davao, except for the amplitude of semidiurnal variations. The deep troughs occur during D-solstice and the enhanced crests during Equinoxes, at both Ancon and Davao.X Anniversary International Conference “Solar-Terrestrial Relations and Physics of Earthquake Precursors”, October 1-5, 2019, Paratunka, Kamchatka region, Russia

Seasonal and long-term variations in the Schumann Resonance observed at Kuju Japan

第150回地球電磁気・地球惑星圏学会（SGEPSS）総会および講演会, 2021年10月31日-11月4

トウナン アジア チイキ ニオケル セキドウ ジェット デンリュウ ノ タイヨウ カツドウ イゾンセイ

赤道ジェット電流(equatorial electrojet: EEJ)は,昼側磁気赤道直下における電離層電気伝導度の局所的増強に起因する電流系である.我々は,波長10.7 cmの太陽電波強度(F10.7)を太陽活動度の指標として用いて,EEJ強度の太陽活動度依存性を調査した.本研究で我々は,MAGDAS/CPMN 観測網のデータを用いて新しく構築されたEEJ指数の一つの成分であるEUEL指数のうち,2011 年の東南アジア地域のデータから算出されたEUEL 指数を解析に用いた.磁気赤道から±3°の狭い緯度帯に集中して流れるEEJ 帯の内側と外側にそれぞれ位置する2 観測点で得られたEUEL 指数の差からEEJ 強度を算出し(2 観測点法),F10.7 強度とEEJ強度に関してパワースペクトル解析と相関解析を行った.その結果,F10.7変動と正相で同期した約24 日と28 日周期を持つEEJ 強度の変動成分の存在を見いだした.一方でEEJ強度の日変化は,解析を行った期間,F10.7 の日変化と,低い相関を示していたことが明らかとなった.A:The equatorial electrojet (EEJ) is a current system caused by the enhanced ionospheric conductivity near the dayside magnetic dip equator. We examined the dependence of the EEJ on solar activity, represented by the 10.7 cm solar radio flux (F10.7). For this analysis, we used a new equatorial electrojet index, EUEL, provided by the MAGDAS/CPMN network in the Southeast Asia sector for the year 2011. Using a two-station method, the EEJ strength was calculated as the difference between the EUEL index of the dip equator station and the EUEL index of the off-dip equator station located outside the narrow channel (±3°in latitudinal range) of the EEJ band. The relationship between the EEJ component and the F10.7 index was then examined using power spectrum and correlation analyses. We found approximate 24-day and 28-day periodicities in the EEJ component, which are in phase with F10.7 variations. On the other hand, the daily values of EEJ showed low correlation with the daily F10.7 variations during the study period

Long-term EEJ variations by using the improved EE-index

In 2008, International Center for Space Weather Science and Education, Kyushu University (ICSWSE) proposed the EE-index, which is an index to monitor the equatorial geomagnetic phenomena. EE-index has been improved with the development of the MAGnetic Data Acquisition System and the Circum-pan Pacific Magnetometer Network (MAGDAS/CPMN) and the enormous archive of MAGDAS/CPMN data over 10 years since the initial article. Using the improved EE-index, we examined the solar cycle variation of equatorial electrojet (EEJ) by the time series analysis for EUEL (one part of EE-index) at Ancon in Peru and the solar activity from September 18, 1998 to March 31, 2015. We found that the long-term variation of daily EEJ peak intensity has a trend similar to that of F10.7 (the solar activity). The power spectrum of the daily EEJ peak has clearly two dominant peaks throughout the analysis interval: 14.5 days and 180 days (semi-annual). The solar cycle variation of daily EEJ peak correlates well with that of F10.7 (the correlation coefficient 0.99). We conclude that the daily EEJ peak intensity is roughly determined as the summation of the long-period trend of the solar activity resulting from the solar cycle and day-to-day variations caused by various sources such as lunar tides, geometric effects, magnetospheric phenomena and atmospheric phenomena. This work presents the primary evidence for solar cycle variations of EEJ on the long-term study of the EE-index.2015 UN/Japan Workshop on Space Weather, 2-6 March 2015, Fukuoka, Japa

Seasonal dependence of semidiurnal equatorial magnetic variation during quiet and disturbed periods

The analysis of 20-year long-term semidiurnal lunar tidal variations gave the evidence that the semidiurnal variations are completely different between the magnetic quiet and disturbed periods. This is the first time that the seasonal dependence of disturbance-time semidiurnal variation has been provided from the analysis of the EE-index. We found the Kp dependence of semidiurnal variation: For full and new moon phase, counter troughs are amplified during disturbance time, possibly related to disturbance dynamo. For all moon phase, there are positive enhancements in dawn and strong depressions after sunset, resulting from the penetration of polar electric filed. For Seasonal dependence, semidiurnal variations are divided to three seasonal groups, and characterized as deep trough, enhanced crest and weak structure for D-solstice, Equinoxes and J-solstice, respectively. There is no significant longitudinal difference between Ancon and Davao, except for the amplitude of semidiurnal variations. The deep troughs occur during D-solstice and the enhanced crests during Equinoxes, at both Ancon and Davao

Equatorial electrojet dependence on solar activity in the Southeast Asia sector

A:The equatorial electrojet (EEJ) is a current system caused by the enhanced ionospheric conductivity near the dayside magnetic dip equator. We examined the dependence of the EEJ on solar activity, represented by the 10.7 cm solar radio flux (F10.7). For this analysis, we used a new equatorial electrojet index, EUEL, provided by the MAGDAS/CPMN network in the Southeast Asia sector for the year 2011. Using a two-station method, the EEJ strength was calculated as the difference between the EUEL index of the dip equator station and the EUEL index of the off-dip equator station located outside the narrow channel (±3°in latitudinal range) of the EEJ band. The relationship between the EEJ component and the F10.7 index was then examined using power spectrum and correlation analyses. We found approximate 24-day and 28-day periodicities in the EEJ component, which are in phase with F10.7 variations. On the other hand, the daily values of EEJ showed low correlation with the daily F10.7 variations during the study period

Monitoring of Space and Earth electromagnetic environment by MAGDAS project: Collaboration with IKIR - Introduction to ICSWSE/MAGDAS project

For study of coupling processes in the Solar-Terrestrial System, International Center for Space Weather Science and Education (ICSWSE), Kyushu University has developed a real time magnetic data acquisition system (the MAGDAS project) around the world. The number of observational sites is increasing every year with the collaboration of host countries. Now at this time, the MAGDAS Project has installed 78 real time magnetometers – so it is the largest magnetometer array in the world. The history of global observation at Kyushu University is over 30 years and number of developed observational sites is over 140. Especially, Collaboration between IKIR is extended back to 1990's. Now a time, we are operating Flux-gate magnetometer and FM-CW Radar. It is one of most important collaboration for space weather monitoring. By using MAGDAS data, ICSWSE produces many types of space weather index, such as EE-index (for monitoring long tern and shot term variation of equatorial electrojet), Pc5 index (for monitoring solar-wind velocity and high energy electron flux), Sq-index (for monitoring global change of ionospheric low and middle latitudinal current system), and Pc3 index (for monitoring of plasma density variation at low latitudes). In this report, we will introduce recent development of MAGDAS/ICSWSE Indexes project and topics for new open policy for MAGDAS data will be also discussed

Schumann resonance parameters at Kuju station during solar flares

We examined the Schumann resonance (SR) at low-latitude station KUJ by comparing with solar X-ray flux and solar proton flux at a geostationary orbit. For intense solar activity in October-November 2003, the reaction of the SR frequency to X-ray enhancement and SPEs was different. The SR frequency in H component increased at the time of the Xray enhancement. The response of SR seems to be caused by the increase of the electron density in the ionospheric D region which ionized by the enhanced solar X-ray flux. In the case of the SPEs, the SR frequency in D component decreased with enhancement of solar proton flux. We suggest that the SPEs caused the decrease of altitude on the ionopheric D region at high-latitude region, and the SR frequency decreased