Keisuke Hosokawa
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View article: Observations of Fragmented Aurora-like Emissions and Picket Fence on the Poleward Edge of the Auroral Oval
Observations of Fragmented Aurora-like Emissions and Picket Fence on the Poleward Edge of the Auroral Oval Open
We analyzed fragmented auroral-like emissions (FAEs) and picket fence structures observed in northern Scandinavia during a magnetic storm on January 1, 2025. The analysis is based on ground-based high-sensitivity optical observations and i…
View article: Strong Substorm Development From Polar‐Cap Arc Laydown Along the Auroral Poleward Boundary
Strong Substorm Development From Polar‐Cap Arc Laydown Along the Auroral Poleward Boundary Open
Meso‐scale enhanced flow channels often extend across the polar cap from the dayside to the nightside auroral oval, where they enter the oval via localized reconnection and cause auroral oval disturbances. Examples here show such flows ass…
View article: Suppression of ion heating in the cusp during plasma flow burst
Suppression of ion heating in the cusp during plasma flow burst Open
Previous studies have shown the occurrence of short-duration plasma flow bursts, typically lasting a few minutes, within the cusp region, often accompanied by the poleward motion of the 630-nm aurora. In this study, we investigated the ion…
View article: Evolution and decay of a stable and a dynamic airglow patch
Evolution and decay of a stable and a dynamic airglow patch Open
View article: Leaping and vortex motion of the shock aurora toward the late evening sector observed on 26 February 2023
Leaping and vortex motion of the shock aurora toward the late evening sector observed on 26 February 2023 Open
On 26 February 2023, a shock aurora triggered by an interplanetary (IP) shock was observed in northern Scandinavia at 21 MLT (magnetic local time). Previously, ground-based observations of shock auroras have primarily been conducted on the…
View article: Ionospheric disturbances associated with the eruption of Mt. Asama observed by TEC data and HF Doppler sounding
Ionospheric disturbances associated with the eruption of Mt. Asama observed by TEC data and HF Doppler sounding Open
Mt. Asama, Nagano Prefecture, Japan, erupted at 11:02 UT on September 1st, 2004. Ionospheric disturbances associated with this eruption were detected using TEC data and HF Doppler observations. It has already been reported that the TEC dat…
View article: Investigation into the earliest generation of medium-scale traveling ionospheric disturbances with electrodynamic signatures using dense GNSS observations over Japan
Investigation into the earliest generation of medium-scale traveling ionospheric disturbances with electrodynamic signatures using dense GNSS observations over Japan Open
Understanding the earliest formation stages of medium-scale traveling ionospheric disturbances (MSTIDs) with electrodynamic signatures (commonly referred to as nighttime MSTIDs) is essential for comprehending their full development. To ana…
View article: Spatio-temporal evolution of the mean energy of the precipitating electron flux in poleward-propagating pulsating auroras
Spatio-temporal evolution of the mean energy of the precipitating electron flux in poleward-propagating pulsating auroras Open
Pulsating auroras (PsAs) blink quasi-periodically, with durations ranging from a few seconds to tens of seconds. They have been classified into several categories based on their motion. These auroras are generated by precipitating electron…
View article: Visualizing the structure and motion of sporadic E layer using marine traffic radio signals
Visualizing the structure and motion of sporadic E layer using marine traffic radio signals Open
The sporadic E layer (EsL), characterized by enhanced ionospheric electron density at around 100 km altitude, has been recognized as one of the prominent phenomena in the E region ionosphere and is known to influence radio wave propagation…
View article: Leaping and vortex motion of the shock aurora toward the late evening sector observed on 26 February 2023
Leaping and vortex motion of the shock aurora toward the late evening sector observed on 26 February 2023 Open
On 26 February 2023, a shock aurora triggered by an interplanetary shock (IP shock) was observed in northern Scandinavia at 21 MLT. Previously, ground-based observations of shock auroras have primarily been conducted on the dayside, where …
View article: Variation of the Altitude of Auroral Emission During a Substorm Cycle: Stereoscopic Optical Observations During the LAMP Rocket Experiment
Variation of the Altitude of Auroral Emission During a Substorm Cycle: Stereoscopic Optical Observations During the LAMP Rocket Experiment Open
We estimated the altitude of aurora by combining data from all‐sky cameras at multiple places which were obtained during the LAMP sounding rocket experiment in Alaska on 5 March 2022. During the launch window of the rocket, three high‐spee…
View article: Observational Evidence for Three Time‐Scale Modulations in the Pulsating Aurora
Observational Evidence for Three Time‐Scale Modulations in the Pulsating Aurora Open
We report an Arase‐all sky imager (ASI) conjugate event in which the pulsating aurora (PsA) has a one‐to‐one correspondence with chorus bursts. Wavelet analysis displayed three peaks at ∼0.3 Hz, 4 Hz, and >10 Hz, corresponding to the main …
View article: On the Factors Controlling the Relationship Between Type of Pulsating Aurora and Energy of Pulsating Auroral Electrons: Simultaneous Observations by Arase Satellite, Ground‐Based All‐Sky Imagers and EISCAT Radar
On the Factors Controlling the Relationship Between Type of Pulsating Aurora and Energy of Pulsating Auroral Electrons: Simultaneous Observations by Arase Satellite, Ground‐Based All‐Sky Imagers and EISCAT Radar Open
Pulsating Aurora (PsA) is one of the major classes of diffuse aurora associated with precipitation of a few to a few tens of keV electrons from the magnetosphere. Recent studies suggested that, during PsA, more energetic (i.e., sub‐relativ…
View article: Exceptionally gigantic aurora in the polar cap on a day when the solar wind almost disappeared
Exceptionally gigantic aurora in the polar cap on a day when the solar wind almost disappeared Open
Revealing the origins of aurorae in Earth’s polar cap has long been a challenge since direct precipitation of energetic electrons from the magnetosphere is not always expected in this region of open magnetic field lines. Here, we introduce…
View article: Post-midnight purple arc and patches appeared on the high latitude part of the auroral oval: Dawnside counterpart of STEVE?
Post-midnight purple arc and patches appeared on the high latitude part of the auroral oval: Dawnside counterpart of STEVE? Open
The phenomenon known as strong thermal emission velocity enhancement (STEVE) is a purple/mauve arc-shaped atmospheric glow observed at lower latitudes of the auroral oval on the duskside. Simultaneous observations using a ground-based came…
View article: New observational projects in New Zealand for studying radiation belt loss processes in the deep inner magnetosphere: instrumentation, operation by solar power and initial results
New observational projects in New Zealand for studying radiation belt loss processes in the deep inner magnetosphere: instrumentation, operation by solar power and initial results Open
This paper describes the instrumentation and the first results of an upper atmospheric observing project conducted in New Zealand. We operate an all-sky aurora camera and a 64-Hz sampling induction magnetometer at Middlemarch, as well as 1…
View article: Periodic oscillations in the high-latitude ionosphere driven by ultralow frequency waves: simultaneous measurements using SuperDARN radars and GNSS-TEC technique
Periodic oscillations in the high-latitude ionosphere driven by ultralow frequency waves: simultaneous measurements using SuperDARN radars and GNSS-TEC technique Open
Analyzing the propagation characteristics of ultralow frequency (ULF: ~1–100 mHz) magnetohydrodynamic waves through ground- and satellite-based magnetometer data offers insights into the plasma conditions within the magnetosphere, plasmasp…
View article: Thermospheric Wind Response to March 2023 Storm: Largest Wind Ever Observed With a Fabry‐Perot Interferometer in Tromsø, Norway Since 2009
Thermospheric Wind Response to March 2023 Storm: Largest Wind Ever Observed With a Fabry‐Perot Interferometer in Tromsø, Norway Since 2009 Open
Solar cycles 24–25 were quiet until a geomagnetic storm with a Sym‐H index of −170 nT occurred in late March 2023. On March 23–24, a Fabry‐Perot interferometer (FPI; 630 nm) in Tromsø, Norway, recorded the highest thermospheric wind speed …
View article: Analysis of Concentric Traveling Ionospheric Disturbances associated with typhoon Faxai in 2019 using HF Doppler Soundings
Analysis of Concentric Traveling Ionospheric Disturbances associated with typhoon Faxai in 2019 using HF Doppler Soundings Open
View article: Clinical features of sleep apnea syndrome and cognitive impairment in multiple sclerosis
Clinical features of sleep apnea syndrome and cognitive impairment in multiple sclerosis Open
View article: Simultaneous Precipitation of Sub‐Relativistic Electron Microburst and Pulsating Aurora Electrons
Simultaneous Precipitation of Sub‐Relativistic Electron Microburst and Pulsating Aurora Electrons Open
We have identified for the first time an energy‐time dispersion of precipitating electron flux in a pulsating aurora patch, ranging from 6.7 to 580 keV, through simultaneous in‐situ observations of sub‐relativistic electrons of microburst …
View article: On the Creation, Depletion, and End of Life of Polar Cap Patches
On the Creation, Depletion, and End of Life of Polar Cap Patches Open
Ionospheric convection patterns from the Super Dual Auroral Radar Network are used to determine the trajectories, transit times, and decay rates of three polar cap patches from their creation in the dayside polar cap ionosphere to their en…
View article: Three-dimensional ionospheric conductivity associated with pulsating auroral patches: reconstruction from ground-based optical observations
Three-dimensional ionospheric conductivity associated with pulsating auroral patches: reconstruction from ground-based optical observations Open
Pulsating auroras (PsAs) appear over a wide area within the aurora oval in the midnight–morning–noon sector. In previous studies, observations by magnetometers on board satellites have reported the presence of field-aligned currents (FACs)…
View article: Anomalous Long‐Distance Propagation of ILS LOC Signals by the Es Layer and Its Impact on Aviation Receivers
Anomalous Long‐Distance Propagation of ILS LOC Signals by the Es Layer and Its Impact on Aviation Receivers Open
Anomalous long‐distance propagation of Very High Frequency radio waves of aeronautical navigation systems was investigated by an airborne Instrument Landing System (ILS) localizer (ILS LOC) receiver installed on the ground at Kure, Japan (…
View article: SuperDARN data for manuscript "Multi-instrument observations of the evolution of polar cap patches associated with flow shears and particle precipitation"
SuperDARN data for manuscript "Multi-instrument observations of the evolution of polar cap patches associated with flow shears and particle precipitation" Open
SuperDARN在14年15月12日2015-<> UT期间的电离层对流数据。
View article: SuperDARN data for manuscript "Multi-instrument observations of the evolution of polar cap patches associated with flow shears and particle precipitation"
SuperDARN data for manuscript "Multi-instrument observations of the evolution of polar cap patches associated with flow shears and particle precipitation" Open
SuperDARN在14年15月12日2015-<> UT期间的电离层对流数据。
View article: Periodic oscillations of Doppler frequency excited by the traveling ionospheric disturbances associated with the Tonga eruption in 2022
Periodic oscillations of Doppler frequency excited by the traveling ionospheric disturbances associated with the Tonga eruption in 2022 Open
The explosive eruption of the Hunga Tonga-Hunga Ha’apai volcano on 15 January 2022 generated atmospheric waves traveling around the Earth, which caused ionospheric disturbances on various spatio-temporal scales. A HF Doppler sounding syste…
View article: Simultaneous observations of equatorial plasma bubbles with an all-sky airglow imager and a HF Doppler sounding system in Taiwan
Simultaneous observations of equatorial plasma bubbles with an all-sky airglow imager and a HF Doppler sounding system in Taiwan Open
High-Frequency Doppler (HFD) sounders at low-latitudes often detect characteristic oblique spreading Doppler traces in the spectrogram, known as Oblique Spread Structure (OSS). OSS has been expected to be generated by the dispersion of rad…
View article: Monitoring of equatorial plasma bubbles using aeronautical navigation system: a feasibility study
Monitoring of equatorial plasma bubbles using aeronautical navigation system: a feasibility study Open
It has long been known that field-aligned irregularities within equatorial plasma bubbles (EPBs) can cause long-range propagation of radio waves in the VHF frequencies such as those used for TV broadcasting through the so-called forward sc…
View article: New Observational Projects in New Zealand for Verification of Radiation Belt Loss Processes in the Deep Inner Magnetosphere: Instrumentation and Initial Results
New Observational Projects in New Zealand for Verification of Radiation Belt Loss Processes in the Deep Inner Magnetosphere: Instrumentation and Initial Results Open
This paper describes the instrumentation of, and the first results from, an upper atmospheric observation project conducted in New Zealand. We operate an all-sky aurora camera and a 64-Hz sampling induction magnetometer at Middlemarch, as …