arXiv subjects

Satoshi Masuda

Publications and source records attributed to Satoshi Masuda.

At least 19 recordsLinked to original sources

arXiv2026

Science operation, data handling, and ground support system of the SOLAR-C mission

SOLAR-C is an international solar-observing satellite mission led by Japan Aerospace Exploration Agency (JAXA). It aims to elucidate mass and energy transport in solar atmospheres through extreme ultraviolet (EUV) spectroscopy. The mission carries the EUV High-throughput Spectroscopic Telescope (EUVST) and the Solar Spectral Irradiance Monitor (SoSpIM), enabling comprehensive observations across a wide temperature range (10^4 K to 10^7 K) with minimum temperature gaps and high spatial and temporal resolution. To achieve its science objectives regarding atmospheric heating and solar flare eruptions, SOLAR-C implements a flexible and responsive operational procedure and a data processing system, while building on the heritage of the Hinode and IRIS satellites. The Chief Observer creates observation timelines that include core observation plans and approved proposed plans while taking into account the solar activity levels. A SpaceWire communication architecture is employed onboard the spacecraft, and a method is implemented in which the mission instrument temporarily acts as the network master during data transfer to support the high data rate requirements. Telemetry is downlinked at ground stations worldwide and gathered at the Institute of Space and Astronautical Science, JAXA. The EUVST data are calibrated at the SOLAR-C Science Center at Nagoya University, while the SoSpIM data are calibrated at the Processing and Archiving Facility before being integrated into the science data products. The data will be made publicly available immediately. The integrated operational scheme for this mission is expected to advance our understanding of solar atmospheric heating and flare processes.

astro-ph.SR↗

arXiv2026

Non-thermal Sources from Stereoscopic Hard X-ray and Earth-based Microwave Observations in a Data-Constrained Magnetohydrodynamic Simulation

We analyze the X7.1 flare on 2024 October 1 from NOAA AR 13842 using hard X-ray (HXR) imaging, microwave observations by the Expanded Owens Valley Solar Array (EOVSA), and a three-dimensional Magnetohydrodynamic (MHD) simulation. The flare was observed from two vantage points, with Solar Orbiter/Spectrometer Telescope for Imaging X-rays viewing the flare near the limb and Advanced Space-based Solar Observatory/Hard X-ray Imager and EOVSA observing it on the disk. We carried out a data-constrained MHD simulation using a nonlinear force-free field extrapolation as the initial condition and constrained the height of the non-thermal looptop source from stereoscopic HXR and microwave observations. The height is consistent between the stereoscopic analysis and the MHD simulation. A secondary non-thermal microwave source aligned with a southward plasma ejection corresponds to an elongated current sheet. Although the current sheet grows in multiple directions, the secondary microwave emission is observed only from the southern segment. This localization suggests reconnection in regions with different magnetic field strengths. Reconnection in strong-field regions produces flare arcades with dominant looptop emission, whereas reconnection in weaker southern regions gives rise to secondary microwave emission at higher altitudes. The height of the secondary source is consistent between the stereoscopic analysis and the MHD simulation. Microwave spectral fitting suggests a higher low-energy cutoff for non-thermal electrons in the secondary microwave source than in the main looptop source. This may reflect the transport of electrons pre-accelerated near the looptop source by the southward plasma ejection.

astro-ph.SR↗

arXiv2026

Stereoscopic Observations of Solar X-ray Sources Explained by a Data-Constrained Magnetohydrodynamic Simulation

We investigated the three-dimensional (3D) magnetic structures and dynamics responsible for particle acceleration in an X7.1-class flare that occurred on October 1, 2024, in NOAA active region 13842. We combined stereoscopic hard X-ray (HXR) observations from the Advanced Space-based Solar Observatory/Hard X-ray Imager (HXI) and the Solar Orbiter/Spectrometer Telescope for Imaging X-rays (STIX) with a 3D magnetohydrodynamic (MHD) simulation constrained by observed photospheric magnetic fields. During the two main peaks of the impulsive phase, HXR footpoints appeared at different locations, indicating a migration of the primary reconnection site in the corona. Our data-constrained MHD simulation successfully reproduced the reconnected field lines linking the observed conjugate HXR footpoints. Furthermore, the simulation shows that these primary reconnections occur along a single quasi-separatrix layer (QSL) system. Therefore, the two main peaks of HXR can be interpreted as episodic energy release within the single QSL system. This study demonstrates that the data-constrained MHD model provides a realistic 3D magnetic context for interpreting HXR emission. Notably, STIX observations revealed a vertically distributed thermal HXR source, extending from the footpoints to the looptop, with its centroid migrating between the two peaks. This marks a first step toward understanding the particle acceleration processes in solar flares.

astro-ph.SR↗

arXiv2025

Generating High-Level Test Cases from Requirements using LLM: An Industry Study

Currently, generating high-level test cases described in natural language from requirement documents is performed manually. In the industry, including companies specializing in software testing, there is a significant demand for the automatic generation of high-level test cases from requirement documents using Large Language Models (LLMs). Efforts to utilize LLMs for requirement analysis are underway. In some cases, retrieval-augmented generation (RAG) is employed for generating high-level test cases using LLMs. However, in practical applications, it is necessary to create a RAG tailored to the knowledge system of each specific application, which is labor-intensive. Moreover, when applying high-level test case generation as a prompt, there is no established method for instructing the generation of high-level test cases at a level applicable to other specifications without using RAG. It is required to establish a method for the automatic generation of high-level test cases that can be generalized across a wider range of requirement documents. In this paper, we propose a method for generating high-level (GHL) test cases from requirement documents using only prompts, without creating RAGs. In the proposed method, first, the requirement document is input into the LLM to generate test design techniques corresponding to the requirement document. Then, high-level test cases are generated for each of the generated test design techniques. Furthermore, we verify an evaluation method based on semantic similarity of the generated high-level test cases. In the experiments, we confirmed the method using datasets from Bluetooth and Mozilla, where requirement documents and high-level test cases are available, achieving macro-recall measurement of 0.81 and 0.37, respectively. We believe that the method is feasible for practical application in generating high-level test cases without using RAG.

cs.SE↗

arXiv2025

Comparison of Polar Magnetic Fields Derived from MILOS and MERLIN Inversions with Hinode/SOT-SP Data

The detailed investigation of the polar magnetic field and its time evolution is one of the major achievements of Hinode. Precise measurements of the polar magnetic field are essential for understanding the solar cycle, as they provide important constraints for identifying the source regions of the solar wind. The Spectropolarimeter (SP) of the Solar Optical Telescope (SOT) on board Hinode has been the instrument best suited to make such measurements. In this study, we compare the SOT-SP data for the polar regions, processed using two representative Milne-Eddington inversion codes, MILOS and MERLIN. These codes are applied to the same level-1 SOT-SP data, and the same disambiguation algorithm is used on the maps that go through the two inversions. We find that the radial magnetic-flux density (the magnetic-flux density with respect to the local vertical) provided by the MERLIN inversion tends to be approximately 7%-10% larger than that obtained from the MILOS inversion. The slightly higher radial magnetic-flux density from MERLIN appears to be common to the polar magnetic fields observed at different phases of the solar cycle. When MILOS is run with the same scattered-light profile and the same magnetic filling factor that are derived with the MERLIN inversion, the radial magnetic-flux density derived from the two inversions is almost the same. We attribute the difference in the radial magnetic-flux density to different filling factors adopted by the two inversions, based on whether the scattered-light profiles are assumed to be the Stokes I profiles averaged over the neighboring pixels or over the entire field of view. The relationship between the radial magnetic-flux density and magnetic filling factor could be more complex in the polar (limb) observations due to the possible contributions of the transverse magnetic-field component to the estimation of the radial magnetic-flux density.

astro-ph.SR↗

arXiv2023

Relationship of peak fluxes of solar radio bursts and X-ray class of solar flares: Application to early great solar flares

Large solar flares occasionally trigger significant space-weather disturbances that affect the technological infrastructures of modern civilization, and therefore require further investigation. Although these solar flares have been monitored by satellite observations since the 1970s, large solar flares occur only infrequently and restrict systematic statistical research owing to data limitations. However, Toyokawa Observatory has operated solar radio observations at low frequencies (at 3.75 and 9.4 GHz) since 1951 and captured the early great flares as solar radio bursts. To estimate the magnitudes of flares that occurred before the start of solar X-ray (SXR) observations with the Geostationary Operational Environmental Satellite (GOES) satellites, we show the relationship between microwave fluxes at 3.75 and 9.4 GHz and X-ray fluxes of flares that occurred after 1988. In total, we explored 341 solar flares observed with the Nobeyama Radio Polarimeters and Toyokawa Observatory from 1988-2014 and compared them with the SXR observations recorded by the GOES satellites. The correlation coefficient was approximately 0.7. Therefore, the GOES X-ray class can be estimated from the peak flux at 3.75 and 9.4 GHz with a large variance and an error of factor of 3 (1 sigma). Thus, for the first time, we quantitatively estimated the light curves of two early solar flares observed in 1956 February by the Toyokawa solar radio observations using the relationship between SXR thermal radiation and microwave nonthermal radiation (Neupert, 1968, ApJ, 153, 59).

astro-ph.SR↗

arXiv2023

Characteristics of the Accelerated Electrons Moving along the Loop Derived from Cyclical Microwave Brightenings at the Footpoints

Many particles are accelerated during solar flares. To understand the acceleration and propagation processes of electrons, we require the pitch-angle distributions of the particles. The pitch angle of accelerated electrons has been estimated from the propagation velocity of a nonthermal microwave source archived in Nobeyama Radioheliograph data. We analyzed a flare event (an M-class flare on 2014 October 22) showing cyclical microwave brightenings at the two footpoint regions. Assuming that the brightenings were caused by the accelerated electrons, we approximated the velocity parallel to the magnetic field of the accelerated electrons as 77,000 and 90,000 km/s. The estimated pitch angle of the accelerated electrons is 69-80 degrees and the size of the loss cone at the footpoint (estimated from the magnetic field strength in the nonlinear force-free field model) is approximately 43 degrees. Most of the accelerated electrons could be reflected at the footpoint region. This feature can be interpreted as brightenings produced by bouncing motion of the accelerated electrons.

astro-ph.SR↗

arXiv2021

Online Adaptation of Parameters using GRU-based Neural Network with BO for Accurate Driving Model

Testing self-driving cars in different areas requires surrounding cars with accordingly different driving styles such as aggressive or conservative styles. A method of numerically measuring and differentiating human driving styles to create a virtual driver with a certain driving style is in demand. However, most methods for measuring human driving styles require thresholds or labels to classify the driving styles, and some require additional questionnaires for drivers about their driving attitude. These limitations are not suitable for creating a large virtual testing environment. Driving models (DMs) simulate human driving styles. Calibrating a DM makes the simulated driving behavior closer to human-driving behavior, and enable the simulation of human-driving cars. Conventional DM-calibrating methods do not take into account that the parameters in a DM vary while driving. These "fixed" calibrating methods cannot reflect an actual interactive driving scenario. In this paper, we propose a DM-calibration method for measuring human driving styles to reproduce real car-following behavior more accurately. The method includes 1) an objective entropy weight method for measuring and clustering human driving styles, and 2) online adaption of DM parameters based on deep learning by combining Bayesian optimization (BO) and a gated recurrent unit neural network. We conducted experiments to evaluate the proposed method, and the results indicate that it can be easily used to measure human driver styles. The experiments also showed that we can calibrate a corresponding DM in a virtual testing environment with up to 26% more accuracy than with fixed calibration methods.

cs.LG↗

arXiv2021

Energy and spectral analysis of confined solar flares from radio and X-ray observations

The energy and spectral shape of radio bursts may help us understand the generation mechanism of solar eruptions, including solar flares, CMEs, eruptive filaments, and various scales of jets. The different kinds of flares may have different characteristics of energy and spectral distribution. In this work, we selected 10 mostly confined flare events during October 2014 to investigate their overall spectral behavior and the energy emitted in microwaves by using radio observations from microwaves to interplanetary radio waves, and X-ray observations of GOES, RHESSI, and Fermi/GBM. We found that: All the confined flare events were associated with a microwave continuum burst extending to frequencies of 9.4 - 15.4 GHz, and the peak frequencies of all confined flare events are higher than 4.995 GHz and lower than or equal to 17 GHz. The median value is around 9 GHz. The microwave burst energy (or fluence) as well as the peak frequency are found to provide useful criteria to estimate the power of solar flares. The observations imply that the magnetic field in confined flares tends to be stronger than that in 412 flares studied by Nita et al. 2004. All 10 events studied did not produce detectable hard X-rays with energies above 300 keV indicating the lack of efficient acceleration of electrons to high energies in the confined flares.

astro-ph.SR↗

arXiv2021

Non-equilibrium Flux Rope Formation by Confined Flares Preceding a Solar Coronal Mass Ejection

We present evidence that a magnetic flux rope was formed before a coronal mass ejection (CME) and its associated long-duration flare during a pair of preceding confined eruptions and associated impulsive flares in a compound event in NOAA Active Region 12371. Extreme-ultraviolet images and the extrapolated nonlinear force-free field show that the first two, impulsive flares, SOL2015-06-21T01:42, result from the confined eruption of highly sheared low-lying flux, presumably a seed flux rope. The eruption spawns a vertical current sheet, where magnetic reconnection creates flare ribbons and loops, a nonthermal microwave source, and a sigmoidal hot channel which can only be interpreted as a magnetic flux rope. Until the subsequent long-duration flare, SOL2015-06-21T02:36, the sigmoid's elbows expand, while its center remains stationary, suggesting non-equilibrium but not yet instability. The "flare reconnection" during the confined eruptions acts like "tether-cutting reconnection" whose flux feeding of the rope leads to instability. The subsequent full eruption is seen as an accelerated rise of the entire hot channel, seamlessly evolving into the fast halo CME. Both the confined and ejective eruptions are consistent with the onset of the torus instability in the dipped decay index profile which results from the region's two-scale magnetic structure. We suggest that the formation or enhancement of a non-equilibrium but stable flux rope by confined eruptions is a generic process occurring prior to many CMEs.

astro-ph.SR↗

arXiv2020

Solar Neutron Decay Protons observed in November 7, 2004

We have found an interesting event registered by the solar neutron telescopes installed at high mountains in Bolivia (5250 m a.s.l.) and Mexico (4600 m a.s.l.). The event was observed November 7th of 2004 in association with a large solar flare of magnitude X2.0. Some features in our registers and in two satellites (GOES 11 and SOHO) reveal the presence of electrons and protons as possible products of neutron decay. Solar neutron decay protons (sndp) were recorded on board ISEE3 satellite in June 3rd, 1982 . On October 19th, 1989, the ground level detectors installed in Goose Bay and Deep River revealed the registration of solar neutron decay protons (sndp). Therefore this is the second example that such an evidence is registered on the Earth's surface.

astro-ph.SR↗

arXiv2020

Multiwavelength Stereoscopic Observation of the May 1, 2013 Solar Flare and CME

A M-class behind-the-limb solar flare on 1 May 2013 (SOL2013-05-01T02:32), accompanied by a ($\sim$ 400 km/s) CME was observed by several space-based observatories with different viewing angles. We investigated the RHESSI-observed occulted hard X-ray emissions that originated at least 0.1 \solrad{} above the flare site. Emissions below $\sim$10 keV revealed a hot, extended (11 MK, >60 arcsec) thermal source from the escaping CME core, with densities around $10^{9}$ cm$^{-3}$. In such a tenuous hot plasma, ionization times scales are several minutes, consistent with the non-detection of the hot CME core in SDO/AIA's 131 \AA{} filter. The non-thermal RHESSI source originated from an even larger area ($\sim$100 arcsec) at lower densities ($10^{8}$ cm$^{-3}$) located above the hot core, but still behind the CME front. This indicates that the observed part of the non-thermal electrons are not responsible for heating the CME core. Possibly the hot core was heated by non-thermal electrons before it became visible from Earth, meaning that the un-occulted part of the non-thermal emission likely originates from a more tenuous part of the CME core, where non-thermal electrons survive long enough to became visible from Earth. Simultaneous hard X-ray spectra from the Mars Odyssey mission, which viewed the flare on disk, indicated that the number of non-thermal electrons $>$20 keV within the high coronal source is $\sim$0.1 - 0.5\% compared to the number within the chromospheric flare ribbons. The detection of high coronal hard X-ray sources in this moderate size event suggests that such sources are likely a common feature within solar eruptive events.

astro-ph.SR↗

arXiv2020

Microwave Study of a Solar Circular Ribbon Flare

A circular ribbon flare SOL2014-12-17T04:51 is studied using the 17/34 GHz maps from the Nobeyama Radioheliograph (NoRH) along with (E)UV and magnetic data from the Solar Dynamics Observatory (SDO). We report the following three findings as important features of the microwave CRF. (1) The first preflare activation comes in the form of a gradual increase of the 17 GHz flux without a counterpart at 34 GHz, which indicates thermal preheating. The first sign of nonthermal activity occurs in the form of stepwise flux increases at both 17 and 34 GHz about 4 min before the impulsive phase. (2) Until the impulsive phase, the microwave emission over the entire active region is in a single polarization state matching the magnetic polarity of the surrounding fields. During and after the impulsive phase, the sign of the 17 GHz polarization state reverses in the core region, which implies a magnetic breakout--type eruption in a fan-spine magnetic structure. (3) The 17 GHz flux around the time of the eruption shows quasi-periodic variations with periods of 1--2 min. The pre-eruption oscillation is more obvious in total intensity at one end of the flare loop, and the post-eruption oscillation, more obvious in the polarized intensity at a region near the inner spine. We interpret this transition as the transfer of oscillatory power from kink mode oscillation to torsional Alfv\'en waves propagating along the spine field after the eruption. We argue that these three processes are inter-related and indicate a breakout process in a fan-spine structure.

astro-ph.SR↗

arXiv2019

Solar Fast Drifting Radio Bursts in an X1.3 Flare on 2014 April 25

One of the most important products of solar flares are nonthermal energetic particles which may carry up to 50\% energy releasing in the flaring processes. In radio observations, nonthermal particles generally manifest as spectral fine structures with fast frequency drifting rates, named as solar fast drifting radio bursts (FDRBs). This work demonstrated three types of FDRBs, including type III pair bursts, narrow band stochastic spike bursts following the type III bursts and spike-like bursts superimposed on type II burst in an X1.3 flare on 2014 April 25. We find that although all of them have fast frequency drifting rates, but they are intrinsically different from each other in frequency bandwidth, drifting rate and the statistical distributions. We suggest that they are possibly generated from different accelerating mechanisms. The type III pair bursts may be triggered by high-energy electron beams accelerated by the flaring magnetic reconnection, spike bursts are produced by the energetic electrons accelerated by a termination shock wave triggered by the fast reconnecting plasma outflows impacting on the flaring looptop, and spike-like bursts are possibly generated by the nonthermal electrons accelerated by moving magnetic reconnection triggered by the interaction between CME and the background magnetized plasma. These results may help us to understand the generation mechanism of nonthermal particles and energy release in solar flares.

astro-ph.SR↗

arXiv2019

Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind Over the Solar Poles

We comparatively studied the long-term variation (1992-2017) in polar brightening observed with the Nobeyama Radioheliograph, the polar solar wind velocity with interplanetary scintillation observations at the Institute for Space-Earth Environmental Research, and the coronal hole distribution computed by potential field calculations of the solar corona using synoptic magnetogram data obtained at Kitt Peak National Solar Observatory. First, by comparing the solar wind velocity (V) and the brightness temperature (T_b) in the polar region, we found good correlation coefficients (CCs) between V and T_b in the polar regions, CC = 0.91 (0.83) for the northern (southern) polar region, and we obtained the V-T_b relationship as V =12.6 (T_b-10,667)^{1/2}+432. We also confirmed that the CC of V-T_b is higher than those of V-B and V-B/f, where B and f are the polar magnetic field strength and magnetic flux expansion rate, respectively. These results indicate that T_b is a more direct parameter than B or B/f for expressing solar wind velocity. Next, we analyzed the long-term variation of the polar brightening and its relation to the area of the polar coronal hole (A). As a result, we found that the polar brightening matches the probability distribution of the predicted coronal hole and that the CC between T_b and A is remarkably high, CC = 0.97. This result indicates that the polar brightening is strongly coupled to the size of the polar coronal hole. Therefore, the reasonable correlation of V-T_b is explained by V-A. In addition, by considering the anti-correlation between A and f found in a previous study, we suggest that the V-T_b relationship is another expression of the Wang-Sheeley relationship (V-1/f) in the polar regions.

astro-ph.SR↗

arXiv2017

Characteristics that Produce White-Light Enhancements in Solar Flares Observed by Hinode/SOT

To understand the conditions that produce white-light (WL) enhancements in solar flares, a statistical analysis of visible continuum data as observed by Hinode/Solar Optical Telescope (SOT) was performed. In this study, approximately 100 flare events from M- and X-class flares were selected. The time period during which the data were recorded spans from January 2011 to February 2016. Of these events, approximately half are classified as white-light flares (WLFs), whereas the remaining events do not show any enhancements of the visible continuum (non-WLF; NWL). In order to determine the existence of WL emission, running difference images of not only the Hinode/SOT WL (G-band, blue, green, and red filter) data but also the Solar Dynamics Observatory/Helioseismic and Magnetic Imager continuum data are used. A comparison between these two groups of WL data in terms of duration, temperature, emission measure of GOES soft X-rays, distance between EUV flare ribbons, strength of hard X-rays, and photospheric magnetic field strength was undertaken. In this statistical study, WLF events are characterized by a shorter time-scale and shorter ribbon distance compared with NWL events. From the scatter plots of the duration of soft X-rays and the energy of non-thermal electrons, a clear distinction between WLF and NWL events can be made. It is found that the precipitation of large amounts of accelerated electrons within a short time period plays a key role in generating WL enhancements. Finally, it was demonstrated that the coronal magnetic field strength in the flare region is one of the most important factors that allow the individual identification of WLF events from NWL events.

astro-ph.SR↗

arXiv2016

Temporal evolution and spatial distribution of white-light flare kernels in a solar flare

On 2011 September 6, we observed an X2.1-class flare in continuum and H$α$ with a frame rate of about 30~Hz. After processing images of the event by using a speckle-masking image reconstruction, we identified white-light (WL) flare ribbons on opposite sides of the magnetic neutral line. We derive the lightcurve decay times of the WL flare kernels at each resolution element by assuming that the kernels consist of one or two components that decay exponentially, starting from the peak time. As a result, 42% of the pixels have two decay-time components with average decay times of 15.6 and 587 s, whereas the average decay time is 254 s for WL kernels with only one decay-time component. The peak intensities of the shorter decay-time component exhibit good spatial correlation with the WL intensity, whereas the peak intensities of the long decay-time components tend to be larger in the early phase of the flare at the inner part of the flare ribbons, close to the magnetic neutral line. The average intensity of the longer decay-time components is 1.78 times higher than that of the shorter decay-time components. If the shorter decay time is determined by either the chromospheric cooling time or the nonthermal ionization timescale and the longer decay time is attributed to the coronal cooling time, this result suggests that WL sources from both regions appear in 42% of the WL kernels and that WL emission of the coronal origin is sometimes stronger than that of chromospheric origin.

astro-ph.SR↗

arXiv2014

Spectral Structures and Their Generation Mechanisms for Solar Radio Type-I Bursts

The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and bandwidth, of the individual burst elements were satisfactorily detected by the highly resolved spectral data of AMATEAS with the burst detection algorithm that is improved in this study. The peak flux of the type-I bursts followed a power-law distribution with a spectral index of 2.9-3.3, whereas their duration and bandwidth were distributed more exponentially. There were almost no correlations between the peak flux, duration, and bandwidth. That means there were no similarity shapes in the burst spectral structures. We defined the growth rate of a burst as the ratio between its peak flux and duration. There was a strong correlation between the growth rate and peak flux. These results suggest that the free energy of type-I bursts that is originally generated by non-thermal electrons is modulated in the subsequent stages of the generation of non-thermal electrons, such as plasma wave generation, radio wave emissions, and propagation. The variation of the time scale of the growth rate is significantly larger than that of the coronal environments. These results can be explained by the situation that the source region may have the inhomogeneity of an ambient plasma environment, such as the boundary of open and closed field lines, and the superposition of entire emitted bursts was observed by the spectrometer.

astro-ph.SR↗