Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

Additional file 2: Figure S2. Same as Additional file 1 but for the July 14, 2012, event

Inner Magnetospheric Response to the Interplanetary Magnetic Field By Component:Van Allen Probes and Arase Observations

We utilise 17 years of combined Van Allen Probes and Arase data to statistically analyse the response of the inner magnetosphere to the orientation of the IMF By component. Past studies have demonstrated that the IMF By component introduces a similarly oriented By component into the magnetosphere. However, these studies have tended to focus on field lines in the magnetotail only reaching as close to Earth as geosynchronous orbit. By exploiting data from these inner magnetospheric spacecraft, we have been able to investigate the response at radial distances of < 7 RE. When subtracting the background magnetic field values, provided by the T01 and IGRF magnetic field models, we find that the IMF By component does affect the configuration of the magnetic field lines in the inner magnetosphere. This control is observed throughout the inner magnetosphere, across both hemispheres, all radial distances, and all MLT sectors. The ratio of IMF By to observed By residual, also known as the "penetration efficiency", is found to be ~0.33. The IMF Bz component is found to increase, or inhibit, this control depending upon its orientation

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

Active auroral arc powered by accelerated electrons from very high altitudes

オーロラ粒子の加速領域が超高高度まで広がっていたことを解明 －オーロラ粒子の加速の定説を覆す発見－. 京都大学プレスリリース. 2021-01-20.Bright, discrete, thin auroral arcs are a typical form of auroras in nightside polar regions. Their light is produced by magnetospheric electrons, accelerated downward to obtain energies of several kilo electron volts by a quasi-static electric field. These electrons collide with and excite thermosphere atoms to higher energy states at altitude of ~ 100 km; relaxation from these states produces the auroral light. The electric potential accelerating the aurora-producing electrons has been reported to lie immediately above the ionosphere, at a few altitudes of thousand kilometres1. However, the highest altitude at which the precipitating electron is accelerated by the parallel potential drop is still unclear. Here, we show that active auroral arcs are powered by electrons accelerated at altitudes reaching greater than 30, 000 km. We employ high-angular resolution electron observations achieved by the Arase satellite in the magnetosphere and optical observations of the aurora from a ground-based all-sky imager. Our observations of electron properties and dynamics resemble those of electron potential acceleration reported from low-altitude satellites except that the acceleration region is much higher than previously assumed. This shows that the dominant auroral acceleration region can extend far above a few thousand kilometres, well within the magnetospheric plasma proper, suggesting formation of the acceleration region by some unknown magnetospheric mechanisms

Magnetic field and energetic particle flux oscillations and high- frequency waves deep in the inner magnetosphere during substorm dipolarization: ERG observations

Using Exploration of energization and Radiation in Geospace (ERG or Arase) spacecraft data, we studied low-frequency magnetic field and energetic particle flux oscillations and high-frequency waves deep in the inner magnetosphere at a radial distance of ~4–5 during substorm dipolarization. The magnetic field oscillated alternately between dipole-like and taillike configuration at a period of 1 min during dipolarization. When the magnetic field was dipole-like, the parallel magnetic component of the Pi2 waves was at trough. Both energetic ion and electron fluxes with a few to tens of kiloelectronvolts enhanced out of phase, indicating that magnetosonic waves were in slow mode. Field-aligned currents also oscillated. These observations are consistent with signatures of ballooning instability. In addition, we found that broadband waves from the Pi1 range to above the electron cyclotron frequency tended to appear intermittently in the central plasma sheet near dipole-like configuration

Mid-latitude Geomagnetic Indices ASY and SYM (ASY/SYM Indices)

【Update frequency】Indices of the previous month are added once a month.　【Observatory Location】[San Juan]geographic latitude: 18.110geographic longitude: 293.850[Fredericksburg]geographic latitude: 38.200geographic longitude: 282.630[Boulder]geographic latitude: 40.130geographic longitude: 254.760[Tucson]geographic latitude: 32.170geographic longitude: 249.270[Honolulu]geographic latitude: 21.320geographic longitude: 202.000[Memambetsu]geographic latitude: 43.910geographic longitude: 144.189[Urumqi]geographic latitude: 43.800geographic longitude: 87.700[Alibag]geographic latitude: 18.638geographic longitude: 72.872[Martin de Vivies]geographic latitude: -37.796geographic longitude: 77.574[Hermanus]geographic latitude: -34.425geographic longitude: 19.225[Chambon-la-Foret]geographic latitude: 48.025geographic longitude: 2.261[Alma-Ata]geographic latitude: 43.250geographic longitude: 76.920　【Citation】World Data Center for Geomagnetism, Kyoto, S. Imajo, A. Matsuoka, H. Toh, and T. Iyemori (2022), Mid-latitude Geomagnetic Indices ASY and SYM (ASY/SYM Indices), doi:10.14989/267216.　【Contact person】Shun Imajo (orcid:0000-0002-9862-844X), Ayako Matsuoka (orcid:0000-0001-5777-9711)The ASY/SYM index was developed by Iyemori [1990] to describe the longitudinally asymmetric and symmetric geomagnetic disturbance fields in middle-latitudes with 1-minute resolution. It is derived from geomagnetic field variations in the H and D components measured at 6 geomagnetic observatories selected from 11 geomagnetic observatories at middle latitudes.1.

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