Yuuki Wada 교수

Abstract Two types of high-energy events have been detected from thunderstorms. One is “terrestrial gamma-ray flashes” (TGFs), sub-millisecond emissions coinciding with lightning discharges. The other is minute-lasting “gamma-ray glows”. Although both phenomena are thought to originate from relativistic runaway electron avalanches in strong electric fields, the connection between them is not well understood. Here we report unequivocal simultaneous detection of a gamma-ray glow termination and a

During a winter thunderstorm on 24 November 2017, a strong burst of gamma rays with energies up to $\ensuremath{\sim}10\text{ }\text{ }\mathrm{MeV}$ was detected coincident with a lightning discharge, by scintillation detectors installed at the Kashiwazaki-Kariwa Nuclear Power Station at sea level in Japan. The burst had a subsecond duration, which is suggestive of photoneutron production. The leading part of the burst was resolved into four intense gamma-ray bunches, each coincident with a low-

In 2015, the Gamma-Ray Observation of Winter Thunderstorms (GROWTH) collaboration launched a mapping observation campaign for high-energy atmospheric phenomena related to thunderstorms and lightning discharges. This campaign has developed a detection network of gamma rays with up to 10 radiation monitors installed in the cities of Kanazawa and Komatsu, Ishikawa Prefecture, Japan, where low-charge-center winter thunderstorms frequently occur. During four winter seasons from October 2016 to April

Abstract During three winter seasons from November 2016 to March 2019, 11 gamma‐ray glows were detected at a single observation site of our ground‐based gamma‐ray monitoring network in Kanazawa, Japan. These events are analyzed with observations of an X‐band radar network, a ceilometer, a disdrometer, and a weather monitor. All the detected glows were connected to convective high‐reflectivity regions of more than 35 dBZ, developed up to an altitude of >2 km. They were also accompanied by heav

Abstract During 2017–2018 winter operation of the Gamma‐Ray Observation of Winter Thunderclouds experiment in Japan, two downward terrestrial gamma‐ray flashes (TGFs) that triggered atmospheric photonuclear reactions were detected. They took place during winter thunderstorms on 5 December 2017 and 9 January 2018 at Kanazawa, Ishikawa Prefecture, Japan. Each event coincided with an intracloud/intercloud discharge, which had a negative‐polarity peak current higher than 150 kA. Their radio waveform

Abstract Winter thunderstorms in Japan have been recognized as an ideal target to observe high‐energy atmospheric phenomena thanks to low‐charge‐center cloud structures. During four winter seasons in Japan (from 2016 October to 2020 March), seven downward terrestrial gamma‐ray flashes (TGFs) were detected by gamma‐ray and broadband low‐frequency (LF: 0.8–500 kHz) monitors. All the detected TGFs took place at the initial stage of lightning flashes. Based on the LF observation, the seven downward

We report on X-ray observations of the Dwarf Nova GK Persei performed by NuSTAR in 2015. GK Persei, behaving also as an Intermediate Polar, exhibited a Dwarf Nova outburst in 2015 March–April. The object was observed with NuSTAR during the outburst state, and again in a quiescent state wherein the 15–50 keV flux was 33 times lower. Using a multitemperature plasma emission and reflection model, the highest plasma temperature in the accretion column was measured as |$19.7^{+1.3}_{-1.0}$| keV in ou

Mitigating ground-clutter signals is one of the major topics for the development of phased array weather radars (PAWRs). Adaptive digital beamforming (DBF) methods have been proposed to reduce ground-clutter effects by making null beam patterns toward the ground. On the other hand, adaptive DBF methods require much higher computational costs than the non-adaptive Fourier DBF method. In the present study, we propose the “precomputed method” for weather radar applications. In this method, a weight

Adaptive digital beamforming (DBF) techniques offer a promising solution for mitigating signals originating from antenna sidelobes, such as clutter echoes from the ground, in phased array weather radars (PAWRs). However, adaptive DBF is sensitive to amplitude and phase errors of reception signals from each antenna element, and its performance can be degraded if antenna elements output large errors. In the present study, we demonstrate a calibration method of amplitude and phase errors by detecti

Abstract We report simulation results of photonuclear reactions in the atmosphere triggered by a downward terrestrial gamma ray flash in lightning. Possible channels of reactions in the atmosphere and their cross‐sections are verified with the ENDF/B‐VII.1 library. Monte Carlo simulations with two stages are then performed with the Geant4 framework. In the first stage, electrons following the relativistic runaway electron avalanche spectrum are produced in a mass model of the atmosphere, and pro

During a winter thunderstorm on 24 November 2017, a downward terrestrial gamma-ray flash took place and triggered photonuclear reactions with atmospheric nitrogen and oxygen nuclei, coincident with a lightning discharge at the Kashiwazaki-Kariwa nuclear power station in Japan. We directly detected neutrons produced by the photonuclear reactions with gadolinium orthosilicate scintillation crystals installed at sea level. Two gadolinium isotopes included in the scintillation crystals, $^{155}\math

Abstract A gamma‐ray glow, a minute‐lasting burst of high‐energy photons from a thundercloud, was detected by ground‐based apparatus at Kanazawa University, Japan, in a winter thunderstorm on 18 December 2018. The gamma‐ray glow was quenched by a lightning flash within a brief time window of 40 ms. The lightning flash produced several low‐frequency (LF) E‐change pulses that were temporally coincident with the termination of the gamma‐ray glow, and that were located within 0.5 km from the observa

Abstract During a winter thunderstorm on 6 February 2017 in Japan, photonuclear reactions such as 14 N( γ , n ) 13 N were triggered by a downward terrestrial gamma‐ray flash (TGF), as reported by Enoto et al. (2017, https://doi.org/10.1038/nature24630 ). In the present paper, we compare the observation with a simulation model of downward TGFs and subsequent photonuclear reactions constructed by the first paper of the series and Wada, Enoto, Nakazawa, et al. (2019, https://doi.org/10.1103/physrev

Abstract The Gamma-ray Observation of Winter Thunderclouds collaboration has detected 70 gamma-ray glows, a high-energy phenomenon associated with thunderstorms, from October 2016 to March 2020 in Kanazawa and Komatsu, Ishikawa Prefecture, a central part of Japan facing the Sea of Japan. Based on surface and 500 hPa analyses, numerical prediction models, and surface and satellite observations, we classify their synoptic meteorological conditions into mainly three types. Most of the glow-detectio

Abstract During the 2020–2021 winter season, we detected 6 gamma‐ray glows at Kanazawa University, Japan. Negative surface electric fields (E‐fields; in the sign convention of atmospheric electricity) were observed by a field mill during all the glow cases. In five of the six cases, the peak E‐field reached around −12 kV m −1 , and the E‐field during the glow detection was the strongest in the interval including 3 hr before and after the detection time. Therefore, negative charges should have be