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Murase, Kiyoka*; Kataoka, Ryuho*; Nishiyama, Takanori*; Sato, Kaoru*; Tsutsumi, Masaki*; Tanaka, Yoshimasa*; Ogawa, Yasunobu*; Sato, Tatsuhiko
Space Weather, 21(12), p.e2023SW003651_1 - e2023SW003651_11, 2023/12
Times Cited Count：0 Percentile：0.01(Astronomy & Astrophysics)Comprehensive understandings of their global impact on the atmosphere require whole pictures of spatio-temporal distributions of the ionization due to them. We estimate the altitude profiles of the ionization rate during the space weather event occurred in September 2017 by using the Particle and Heavy Ion Transport code System (PHITS) with input of the particle fluxes obtained by satellites. The estimates are then compared with measurements of the ionization altitude, ionization intensity, and electron density by the radars in the polar region such as the PANSY radar at Syowa Station and the EISCAT in Tromso, Norway. We conclude that the PHITS simulation results reproduce those ionizations measured by ground-based instruments with inputs of observed ionization sources by satellites within a factor of 2.
Kataoka, Ryuho*; Sato, Tatsuhiko; Kato, Chihiro*; Kadokura, Akira*; Kozai, Masayoshi*; Miyake, Shoko*; Murase, Kiyoka*; Yoshida, Rihito*; Tomikawa, Yoshihiro*; Munakata, Kazuoki*
Journal of Space Weather and Space Climate (Internet), 12, p.37_1 - 37_11, 2022/11
Times Cited Count：1 Percentile：20.65(Astronomy & Astrophysics)Solar modulation of galactic cosmic rays around the solar minimum in 2019-2020 looks different in the secondary neutrons and muons observed at the ground. To compare the solar modulation of primary cosmic rays in detail, we have to remove the possible seasonal variations caused by the atmosphere and surrounding environment. As such surrounding environment effects, we evaluate the snow cover effect on neutron count rate and the atmospheric temperature effect on muon count rate both simultaneously observed at Syowa Station in the Antarctic (69.01
S, 39.59 E). The corrected muon count rate starts decreasing in late 2019, earlier than the corrected neutron count rate which starts decreasing in early 2020, possibly indicating the rigidity dependent solar modulation in the heliosphere.
Murase, Kiyoka*; Kataoka, Ryuho*; Nishiyama, Takanori*; Nishimura, Koji*; Hashimoto, Taishi*; Tanaka, Yoshimasa*; Kadokura, Akira*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Ogawa, Yasunobu*; et al.
Journal of Space Weather and Space Climate (Internet), 12, p.18_1 - 18_16, 2022/06
Times Cited Count：1 Percentile：20.65(Astronomy & Astrophysics)We identified two energetic electron precipitation (EEP) events during the growth phase of moderate substorms and estimated the mesospheric ionization rate for an EEP event for which the most comprehensive dataset from ground-based and space-born instruments was available. The mesospheric ionization signature reached below 70 km altitude and continued for ~15 min until the substorm onset, as observed by the PANSY radar and imaging riometer at Syowa Station in the Antarctic region. We also used energetic electron flux observed by the Arase and POES 15 satellites as the input for the air-shower simulation code PHITS to quantitatively estimate the mesospheric ionization rate. Combining the cutting-edge observations and simulations, we shed new light on the space weather impact of the EEP events during geomagnetically quiet times, which is important to understand the possible link between the space environment and climate.
Sato, Tatsuhiko; Kataoka, Ryuho*; Shiota, Daiko*; Kubo, Yuki*; Ishii, Mamoru*; Yasuda, Hiroshi*; Miyake, Shoko*; Miyoshi, Yoshizumi*; Ueno, Haruka*; Nagamatsu, Aiko*
Journal of Space Weather and Space Climate (Internet), 9, p.A9_1 - A9_11, 2019/03
Times Cited Count：7 Percentile：38.15(Astronomy & Astrophysics)Real-time estimation of astronaut doses during solar particle events (SPE) is one of the most challenging tasks in cosmic-ray dosimetry. We therefore develop a new computational method that can nowcast the solar energetic particle (SEP) as well as galactic cosmic-ray (GCR) fluxes on any Earth orbit during a large SPE associating with ground level enhancement. It is an extended version of WArning System for AVIation Exposure to Solar Energetic Particle, WASAVIES. The extended version, called WASAVIES-EO, can calculate the GCR and SEP fluxes outside a satellite based on its two-line element data. Moreover, organ dose and dose-equivalent rates of astronauts in the International Space Station (ISS) can be estimated using the system, considering its shielding effect. The accuracy of WASAVIES-EO was validated based on the dose rates measured in ISS, as well as based on high-energy proton fluxes observed by POES satellites.
Kataoka, Ryuho*; Sato, Tatsuhiko; Miyake, Shoko*; Shiota, Daiko*; Kubo, Yuki*
Space Weather, 16(7), p.917 - 923, 2018/07
Times Cited Count：19 Percentile：69.21(Astronomy & Astrophysics)A ground level enhancement (GLE) event occurred on 10-11 September 2017, associated with X8.2 solar flare exploded at western limb. The magnitude of the GLE was not so large even at the peak, but the duration of the event was longer than average. We briefly report the results of our manually conducted nowcast using WASAVIES (Warning System of AViation Exposure to Solar energetic particles). The maximum radiation dose rate at 12 km flight altitude was estimated to be approximately 2 
Sv/h, which is only one-third of the corresponding background dose rate due to the galactic cosmic-ray exposure. This result verified the safety of aircrews and passengers in aviation during this event.
Sato, Tatsuhiko; Kataoka, Ryuho*; Shiota, Daiko*; Kubo, Yuki*; Ishii, Mamoru*; Yasuda, Hiroshi*; Miyake, Shoko*; Park, I.*; Miyoshi, Yoshizumi*
Space Weather, 16(7), p.924 - 936, 2018/07
Times Cited Count：20 Percentile：69.21(Astronomy & Astrophysics)A physics-based warning system of aviation exposure to solar energetic particles, WASAVIES, is improved to be capable of real-time and automatic analysis. In the improved system, the count rates of several neutron monitors (NM) at the ground level, as well as the proton fluxes measured by the GOES satellite are continuously downloaded at intervals of 5 min and used for determining the model parameters. The performance of WASAVIES is examined by analyzing the three major GLE events of the 21st century. A web-interface of WASAVIES is also developed and will be released in the near future through the public server of NICT.
Miyake, Shoko*; Kataoka, Ryuho*; Sato, Tatsuhiko
Space Weather, 15(4), p.589 - 605, 2017/04
Times Cited Count：19 Percentile：63.41(Astronomy & Astrophysics)Weak solar activity and high cosmic-ray flux during the coming solar cycle are qualitatively anticipated by the recent observation that show the decline in the solar activity levels. We have quantitatively predicted the cosmic-ray modulation and resultant radiation exposure at flight altitude by using the time-dependent and three dimensional model of the cosmic-ray modulation. The database of airshower simulation performed by Particle and Heavy Ion Transport code System, PHITS, was employed in the prediction. Our predictions of the neutron monitor counting rate and the radiation dose of aircrews during the solar cycle 24/25 have some natures caused by the charge sign dependence of the cosmic-ray modulation, such as the flat-top profiles.
Matthi
, D.*; Ehresmann, B.*; Lohf, H.*; K
hler, J.*; Zeitlin, C.*; Appel, J.*; Sato, Tatsuhiko; Slaba, T. C.*; Martin, C.*; Berger, T.*; et al.
Journal of Space Weather and Space Climate (Internet), 6, p.A13_1 - A13_17, 2016/03
Times Cited Count：66 Percentile：93.52(Astronomy & Astrophysics)The Radiation Assessment Detector (RAD) on the Mars Science Laboratory (MSL) has been measuring the radiation environment on the surface of Mars since August 6th 2012. In this work, several models such as GEANT4, PHITS, and HZETRN/OLTARIS are used to predict the radiation environment caused by galactic cosmic rays on Mars in order to compare and validate them with the experimental results. Although good agreement is found in many cases for GEANT4, PHITS and HZETRN/OLTARIS, some models still show large, sometimes order of magnitude, discrepancies in certain particle spectra. We have found that RAD data is helping make better choices of input parameters and physical models. These results help to predict dose rates for future manned missions as well as to perform shield optimization studies.
Kataoka, Ryuho*; Sato, Tatsuhiko; Kubo, Yuki*; Shiota, Daiko*; Kuwabara, Takao*; Yashiro, Seiji*; Yasuda, Hiroshi*
Space Weather, 12(6), p.380 - 386, 2014/06
Times Cited Count：19 Percentile：51.52(Astronomy & Astrophysics)Solar energetic particles (SEP) sometimes induce air shower that significantly increase the radiation dose at flight altitudes. In order to inform the situation of such a space radiation hazard to aircrews, a physics-based forward model is developed as WASAVIES (Warning System for Aviation Exposure to SEP) based on the focused transport equation and Monte Carlo particle transport simulation of the air shower. WASAVIES gives the fastest and simplest way to predict the time profile of dose rate during ground-level enhancements (GLEs).
Kataoka, Ryuho*; Sato, Tatsuhiko; Yasuda, Hiroshi*
Space Weather, 9(8), p.S08004_1 - S08004_2, 2011/08
Times Cited Count：12 Percentile：35.93(Astronomy & Astrophysics)We held a half day session entitled "Predicting radiation dose from solar energetic particles" in the Japan Geoscience Union 2011 Meeting on 24 May 2011, in response to increasing public interest for space radiation dose during the ascending phase of the solar cycle 24. This is the first session in Japan to discuss the fundamental problems to predict the aviation radiation dose from SEP, provides a unique start point of an interdisciplinary approach.
