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The relationship between solar wind conditions and substorm activity is modelled with an approach based on an echo state network. Substorms are a fundamental physical phenomenon in the magnetosphere–ionosphere system, but the deterministic prediction of substorm onset is very difficult because the physical processes that underlie substorm occurrences are complex. To model the relationship between substorm activity and solar wind conditions, we treat substorm onset as a stochastic phenomenon and represent the stochastic occurrences of substorms with a nonstationary Poisson process. The occurrence rate of substorms is then described with an echo state network model. We apply this approach to two kinds of substorm onset proxies. One is a sequence of substorm onsets identified from auroral electrojet intensity and the other is onset events identified from Pi2 activity. We then analyse the response of substorm activity to solar wind conditions by feeding synthetic solar wind data into the echo state network. The results indicate that the effect of the solar wind speed is important, especially for Pi2 substorms. A Pi2 pulsation can often occur even if the interplanetary magnetic field (IMF) is northward, while the activity of auroral electrojets is depressed during northward IMF conditions. We also observe spiky enhancements in the occurrence rate of substorms when the solar wind density abruptly increases, which might suggest an external triggering due to a sudden impulse of solar wind dynamic pressure. It seems that northward turning of the IMF also contributes to substorm occurrences, though the effect is likely to be minor.

Large-amplitude meteotsunamis were observed in many areas in Japan, following the arrival of barometric Lamb waves emitted by an underwater volcanic eruption of Hunga Tonga-Hunga Ha‘apai in January 2022. We modeled the power spectra of the tidal level data obtained from 12 tide stations of the Geospatial Information Authority of Japan, based on a method of transfer function which converts the barometric pressure pulse spectra into the meteotsunami spectra. The obtained transfer functions are similar at 12 stations. The pressure pulse spectra are obtained from the ensemble average of ∼1500 Soratena weather sensors of Weathernews Inc. distributed over Japan. The observed meteotsunami spectra can be characterized by the enhanced seiche eigenmodes at each station excited by the mesoscale pressure pulse within the amplitude error of 50%, which contributes for accumulating the necessary knowledge to understand the potential dangers in various different areas over Japan.

Physics-based simulations are important for elucidating the fundamental mechanisms behind the time-varying complex ionospheric conditions, such as field-aligned currents (FACs) and plasma convection patterns, against unprecedented solar wind variations incidents in the Earth’s magnetosphere. However, to perform a huge parameter survey for understanding the nonlinear solar wind density dependence of the FAC and convection patterns, for example, a large-scale cluster computer is not fast enough to run state-of-the-art global magnetohydrodynamic (MHD) simulations. Here we report the impressive performance of a machine-learning based surrogate model for the ionospheric outputs of a global MHD simulation, using the reservoir computing technique called echo state network (ESN). The trained ESN-based emulator is exceptionally fast to perform the parameter survey, suggesting a missing solar wind density dependence of the ionospheric polar cap potential. We discuss future directions including the promising application for the space weather forecast.

The 13th Symposium on Polar Science/Ordinary sessions [OS] Space and upper atmospheric sciences, Wed. 16 Nov.

The 13th Symposium on Polar Science/Ordinary sessions [OS] Space and upper atmospheric sciences, Wed. 16 Nov.

The 13th Symposium on Polar Science/Ordinary sessions [OS] Space and upper atmospheric sciences, Wed. 16 Nov.

The 13th Symposium on Polar Science/Ordinary sessions [OS] Space and upper atmospheric sciences, Wed. 16 Nov.

The 13th Symposium on Polar Science/Ordinary sessions [OS] Space and upper atmospheric sciences, Wed. 16 Nov.

The 13th Symposium on Polar Science/Ordinary sessions [OS] Space and upper atmospheric sciences, Wed. 16 Nov.

The 13th Symposium on Polar Science/Ordinary sessions [OS] Space and upper atmospheric sciences, Wed. 16 Nov.

The 13th Symposium on Polar Science/Special session [S] Towards the next six-year Japanese Antarctic Research Project (phase X), Tue. 15 Nov.

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 must 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). A machine learning technique, Echo State Network (ESN), is applied to estimate both effects hidden in the observed time series of the count rate. We show that the ESN with the input of ERA5 reanalysis data (temperature time series at 1000, 700, 500, 300, 200, 100, 70, 50, 30, 20, and 10 hPa) at the closet position can be useful for both the temperature correction for muons and snow cover correction for neutrons. 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.

The accidental reentry of 38 Starlink satellites occurred in early February 2022, associated with the occurrence of moderate magnetic storms. A poorly understood structure of Coronal Mass Ejections (CMEs) caused the magnetic storms at unexpected timing. Therefore, a better understanding of minor CME structures is necessary for the modern space weather forecast. During this event, the “up to 50%” enhancement of air drag force was observed at ~200 km altitude, preventing the satellites’ safety operations. Although the mass density enhancement predicted by the NRLMSIS2.0 empirical model is less than 25% under the present moderate magnetic storms, the real-time GAIA simulation showed a mass density enhancement of up to 50%. Further, the real-time GAIA simulation suggests that the actual thermospheric disturbances at 200 km altitude may occur with larger amplitude in a broader area than previously thought.

Solar energetic particles (SEPs) are high-energetic particles that consist mainly of electrons and protons with energies from a few tens of keV to GeV ejected associated with solar flares and coronal mass ejections. SEPs can precipitate into planetary atmospheres cause ionization, excitation and dissociation of atmospheric molecules, leading to changes in atmospheric chemical composition via chemical network [e.g. Solomon et al., 1981; Adams et al., 2021].The effect of SEPs on ozone concentration in the Earth’s polar region has been intensively studied for the past decades. For instance, during the enormous solar flare that occurred in late October 2003, NOx and HOx concentrations were enhanced and ozone concentration was depleted by 40% at the polar lower mesosphere [e.g. Jackman et al., 2005]. Increased ionization and dissociation of atmospheric N2 and O2molecules led to the production of NOx and HOx, which catalytically destroyed ozone at the polar mesosphere.Recently, the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has discovered global diffuse aurora on the nightside of Mars down to few tens km in altitude during SEP events, indicating that a significant amount of energy could be deposited in the atmosphere deeper than previously thought [Schneider et al., 2015; Nakamura et al., 2022]. However, the effects of SEPs on the atmospheric chemistry of present-day Mars have not yet been investigated by observations and/or models.By coupling a Monte Carlo model PTRIP (Nakamura et al., 2022) and a newly developed photochemical model to investigate the effects of SEPs on the atmospheric compositions at Mars, we performed a simulation to track the effects of a large SEP event on the Martian atmospheric composition. We found that HOx increased by a factor of 10 and ozone decreased by a factor of 10 in the altitude range from 20 km to 60 km. This is the very first estimation of the effects of SEPs on the atmospheric neutral compositions at Mars, indicating that similar effects on HOx and ozone could be expected on Mars than on Earth.

日本最古の天文現象の記録は、『日本書紀』巻二十二、推古二十八年十二月一日（西暦六二〇年十二月三十日）の條に記される「十二月庚寅朔、天有赤気。長一丈餘。形似雉尾」という一節である。「赤気」は、彗星の類と理解され、日本古典文学や歴史学などの研究では悪い兆候を示すもの、といった理解がなされてきた。その一方、地球物理学においては、オーロラと理解され、オーロラの最も早い事例としてこの『日本書紀』が位置づけられてきた経緯がある。今回の考察では、「赤気」だけではなく、文中の「雉尾」という言葉にも着目し、『日本書紀』諸本での記述を踏まえたうえで、扇形をした赤いオーロラが日本などの中緯度で観察されやすく、真夜中より前に見られ、かつ雉の尾に似た形状をし、「長一丈」に該当する角距離十度相当で見えるという最も構造が際立った形態であるということを、雉の生態など、鳥類学の研究も踏まえて明らかにした。文献学的な考察に加え、雉の生態や尾羽の特徴を理解する鳥類学、彗星に関する古天文学の知識も合わせて新たな考察を加えたことによって、『日本書紀』の編纂に当たった人々の記述に対する責任感や知性、私たち日本人のルーツとなった倭の人々の観察眼や感性を伺い知るうえで一定の視点を与えることに寄与しうるものである。The oldest record of an astronomical phenomenon in Japan was recorded in the Nihon-shoki as follows: “On December 30 in 620, a red sign appeared in heaven. The length was more than 1 jo (10 degrees). The shape was similar to a pheasant tail (Suiko-Tennou, 28)”. The appearance of a red sign has been recognized as an expression of a bad omen in literature, while it has been interpreted as the northern lights in geophysics. First we examine the description of the pheasant tail in detail. We then introduce the latest scientific findings that the northern lights show a fan-shaped appearance with a red background when appearing over Japan. After showing that the fan-shape is similar to a pheasant tail, also pointing out the low possibility of comets, we conclude that the oldest record of the red sign is consistent with the appearance of the northern lights over Japan. We hope that this examination contributes to increasing awareness of the sensitivity of Japanese people 1400-years-ago who compared a beautiful behavior of birds with a magnificent and rare natural phenomenon.

International audience; The Solar Energetic Particle and Imaging UltraViolet Spectrograph (IUVS) instruments onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft discovered diffuse aurora that span across the nightside of Mars due to the interaction of solar energetic particles (SEPs) with the Martian atmosphere. However, it is unclear whether the diffuse aurora originates from energetic electrons or protons. We have developed a Monte Carlo model to calculate the limb intensity profile of the CO2+ ultraviolet doublet (UVD) due to precipitation of energetic electrons and protons with energy ranges from 100 eV to 100 keV and from 50 keV to 5 MeV, respectively. We used electron and proton fluxes observed by MAVEN during the December 2014 SEP event and the September 2017 SEP event. Our results showed that proton-induced CO2+ UVD emission has a lower peak altitude than electron-induced CO2+ UVD emission. The calculated peak altitudes of the CO2+ UVD limb profiles are 76 km and 68 km in the December 2014 event and the September 2017 event, respectively. Extending the energy to 500 keV for electrons and 20 MeV for protons further improved our comparison to the IUVS observations. We have succeeded in reproducing peak altitudes and shapes of the observed CO2+ UVD limb profiles using the SEP flux observed by MAVEN. This was possible by taking into account the contribution of energetic protons, indicating that both energetic electrons and protons contribute to producing the observed diffuse aurora.

著者人数: 29名, Accepted: 2019-09-02, 資料番号: SA1190133000

The properties of the auroral electrojets are examined on the basis of a trained machine learning model. The relationships between solar-wind parameters and the AU and AL indices are modeled with an echo state network (ESN), a kind of recurrent neural network. We can consider this trained ESN model to represent nonlinear effects of the solar-wind inputs on the auroral electrojets. To identify the properties of auroral electrojets, we obtain various synthetic AU and AL data by using various artificial inputs with the trained ESN. The analyses of various synthetic data show that the AU and AL indices are mainly controlled by the solar-wind speed in addition to Bz of the interplanetary magnetic field (IMF) as suggested by the literature. The results also indicate that the solar-wind density effect is emphasized when solar-wind speed is high and when IMF Bz is near zero. This suggests some nonlinear effects of the solar-wind density.

Although solar activity may significantly impact the global environment and socioeconomic systems, the mechanisms for solar eruptions and the subsequent processes have not yet been fully understood. Thus, modern society supported by advanced information systems is at risk from severe space weather disturbances. Project for solar–terrestrial environment prediction (PSTEP) was launched to improve this situation through synergy between basic science research and operational forecast. The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. By this project, we sought to answer the fundamental questions concerning the solar–terrestrial environment and aimed to build a next-generation space weather forecast system to prepare for severe space weather disasters. The PSTEP consists of four research groups and proposal-based research units. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.

The ISS-based Calorimetric Electron Telescope (CALET) is directly measuring the energy spec- trum of electron+positron cosmic rays up to 20 TeV. Cosmic-ray electrons of TeV region energy are limited by energy loss to a propagation range of about 1 kpc, therefore the expected sources are a few nearby supernova remnants (SNR), with the Vela SNR dominating the spectrum. The latest spectrum measured by CALET in combination with the positron-only flux published by AMS-02 is fitted with a comprehensive model including nearby pulsars as the source of the positron excess. This model is extended to the TeV region by addition of the flux from the Vela SNR as calculated with DRAGON, with the integrated energy emitted in electron cosmic rays by the SNR as a variable scale factor. Exploring various scenarios for the time and energy dependence of the cosmic-ray release from Vela, under varied propagation conditions, best-fitting interpretations of the spectrum and upper limits on the emission of cosmic-ray electrons by Vela have been derived.