令和4年度 総合解析セミナー
日時： 金曜 15:00 - 16:30
場所： ZOOM （参加ご希望の方は nakamura.satoko[at]isee.nagoya-u.ac.jp まで事前にご連絡ください。
[at]は@に置き換えてください。）
| date | Speaker | title |
|---|---|---|
| 2/17 | Nobata Masahiro | Verification of the inversion method for electric field and velocity on the photosphere |
| Abstract : To understand the mechanism of solar flares and coronal activity, it is necessary to investigate the three-dimensional structure of the solar coronal magnetic field. However, since the coronal magnetic field cannot be observed directly, a data-driven MHD simulation that numerically reproduces the coronal magnetic field from the observation data of the photospheric magnetic field has recently been developed. To conduct a data-driven simulation, we must determine the electric and velocity fields on the photosphere as boundary conditions. Several methods have recently been developed to do this. For instance, Fisher et al. (2010) developed a method for this purpose, exploiting the vector magnetic field's poloidal-toroidal decomposition (PTD). Kaneko et al. (2021) used this method to simulate observed mesoscale flares successfully. However, it has not been quantitatively investigated how accurately the PTD reproduces the electric and velocity fields and the dependencies of the PTD on the observation parameters. The objective of this study is to quantitatively evaluate the reproducibility of the electric field and velocity field by PTD. Therefore, we used the Spaceweather HMI Active Region Patch (SHARP) data observed by the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO) satellite. We used the SHARP of the active region NOAA 11302 and produced the two vector magnetograms by uniformly shifting the SHARP data in a certain spatial direction. The two magnetograms correspond to sequential data in which the magnetic field is uniformly advected for a constant time at a certain velocity. Therefore, the reproducibility can be evaluated quantitatively by comparing the velocities and electric fields reproduced from the two magnetograms with the advective velocities and the corresponding electric fields. As a result, we found that the reproduction of the electric field is relatively good in the strong magnetic field region, while the electric field is hardly reproduced in the region where the magnetic field is weaker than 1000G. It was also found that the reproduced electric field tends to be smaller than the true value, even in the strong magnetic field region. In addition, we will investigate the dependency of the reproducibility on the time interval and spatial structure of the observed magnetic field. We also report on the reproduction experiment using the MHD simulations of the emerging flux. | ||
| 2/10 | Obayashi Yuya | Wave-particle interactions with lower band whistler-mode chorus waves (LBC) near the equator result in electron precipitation with en |
| Abstract : Wave-particle interactions with lower band whistler-mode chorus waves (LBC) near the equator result in electron precipitation with energies ranging from 1-100 keV, leading to the pulsating aurora (PsA). Recent studies have shown that sub-relativistic/relativistic electrons with energies of several hundred of keV to several MeV are scattered by chorus waves that propagates to high latitudes along the field line, and these electrons precipitate into the mesosphere at an altitude of 60-80 km simultaneously with PsA (Miyoshi et al., 2015, 2020, 2021). We investigate high-energy electron precipitation during PsA events at Tromsø, Norway, from 02:00 to 06:00 UT on March 12, 2022, using data from the Arase satellite and the EISCAT radar. We estimate the electron energy spectrum from EISCAT observations. The analysis confirmed that electron precipitation occurred in wide energy range, and particularly strong precipitation was observed at energies of several tens of keV, and the estimated maximum energy of the precipitating electrons is ~300 keV. We then derived the pitch angle diffusion coefficient of electrons through chorus wave particle interactions using the Arase/PWE OFA data. Our result indicates that the estimated life time from a quasi-linear theory is comparable to the theoretical strong diffusion limit, implying that the observed plasma waves in the magnetosphere drive strong precipitation observed by the EISCAT radar. Moreover, our analysis confirms that chorus waves propagate to the higher latitudes can resonate more energetic electrons as shown in the estimation of the pitch angle diffusion coefficient. Considering these analyses, we conclude that the pitch angle scattering by LBC along the field line leads to wide energy electron precipitation from a few keV to more than 100 keV during PsA, as observed by the EISCAT radar. | ||
| 2/3 | Kenya Terasawa | Direct detection of proton pitch angle scattering by EMIC waves: Arase observations |
| Abstract : Energy exchange between charged particles and electromagnetic ion cyclotron waves (EMIC waves) have been supposed to contribute acceleration and scattering of ions in the magnetosphere.It has been suggested theoretically that when energy is transferred from ions to EMIC waves, the pitch angle of ions decreases and ions precipitate into the Earth's ionosphere. It was difficult for conventional observations to measure changes of pitch angle and energy through wave-particle interaction. We have developed the WPIA method that can directly calculate the phase differences between the velocity vector of gyrating ions and electric/magnetic fields of EMIC waves, and the method successfully detected energy exchange between EMIC waves and ions associated with rising tone (Shoji+, 2017) and falling tone (Shoji+, 2021). However, there have been no studies about the pitch angle scattering of protons by EMIC waves with the WPIA methods. On June 21, 2021, the Arase satellite successfully observed intense EMIC waves by PWE/EFD and MGF and deformation of the pitch angle distribution of ions by LEPi simultaneously. For this event, we applied the WPIA analysis and calculated v x B as well as v・E. The results show that significant Lorentz force works to decrease pitch angles of ions. At the same time, several protons increase their energy with increasing their pitch angles. These are the first direct evidence of the pitch angle scattering between EMIC waves and ions in the space plasma. In this presentation, we discuss what parameters contribute to the saturation and decay of EMIC wave amplitudes. | ||
| 2/3 | Yuta Nishimiya | Development of outer radiation belt forecast model with XAI(放射線帯外帯電子変動予測モデルの開発とXAIによるモデル解釈) |
| Abstract : The radiation belt is the region in the inner magnetosphere where the most energetic electrons are trapped by the Earth's magnetic field. Especially in the outer radiation belt, the spatial and temporal variations of the electron flux are particularly large, and a sustained increase in the outer belt electron intensity may lead to satellite anomaly. The prediction of energetic electron flux variations is therefore of significant importance in mitigating these risks. We have developed an outer radiation belt electron forecast model that utilizes Recurrent Neural Network (RNN) and Long Short-Term Memory (LSTM) techniques. This model is designed to forecast the time-variant electron flux in the outer radiation belt, with energies ranging from several hundred keV to several MeV at L=4-6, using solar wind velocity, IMF, and the outer radiation belt electron flux from the past three days as inputs. However, the small prediction accuracy is found when the flux decreases at high L values. To address this issue, we have improved the model by incorporating additional solar wind parameters. Previous research has indicated that the solar wind dynamic pressure contributes to the loss of energetic electrons via magnetopause shadowing, and thus including this parameter as an input may enhance the forecast accuracy. Our revised model that incorporates the solar wind dynamic pressure as an input demonstrates improved prediction accuracy. Moreover, we have incorporated Explainable Artificial Intelligence (XAI) into the model to investigate the impact of each input parameter on the electron flux. | ||
| 1/27 | Shun Idei | Time-varying characteristics observed in geomagnetically induced currents in Japan (日本における地磁気誘導電流に見られる時間変化特性について) |
| Abstract : Geomagnetically Induced Current (GIC) generated by various space physics phenomena such as magnetic storms pose a risk to the power grid in the form of malfunctions of transmission line protection relays and loss of power due to half-period saturation, and also in the form of insulation performance degradation due to hot spot heating. However, in low magnetic latitudes such as Japan, the magnetic field fluctuations of magnetic storms are only about 1/10 or less of those at high latitudes, so the risk of damage to the power grid from GIC is considered to be low and research is not yet advanced. However, the fact that several phenomena that are likely to be caused by GIC have actually been reported from mid- and low-latitude regions, and that small-scale GIC that occur routinely in Japan may be causing power losses, calls for the need to clarify the characteristics of GIC in Japan. Our study focuses on the observed data of GIC that occurred at the New Tsukuba Substation from 2018 to 2020, and analyses the temporal and seasonal characteristics of GIC from statistical analysis, as well as events with relatively large GIC during the period. | ||
| 1/27 | Riku Ozaki | Higher order integrators for relativistic equations of motion for charged particles (相対論的運動方程式の高次精度数値解析手法の研究) |
| Abstract : The purpose of this study is to improve the numerical method for integrating the relativistic equation of motion for charged particles. The Runge-Kutta integrator (RK4) is a classical method for numerically solving various difference equations. Although RK4 has a fourth order accuracy in time, RK4 does not satisfy the conservation laws in the relativistic motion of charged particles. The Boris integrator [1], which has the second order accuracy in time, has been used conventionally. Although the Boris method satisfies the energy conservation law during the gyro motion of charged particles, the numerical error is larger with a larger relativistic Lorentz factor. Recently, a new integrator has been developed based on the theoretical solution to the relativistic equation of motion for charged particles [2], which is called as the Umeda integrator. The Umeda integrator conserves the boosted Lorentz factor and gives the exact E-cross-B drift velocity. However, the Umeda integrator has the second order accuracy in time and less accurate than RK4. In this study, we develop advanced integrator with higher order accuracy. First, the Umeda integrator has been improved by using multi-step (multi-stage) Runge-Kutta integrators. Second, the Taylor series expansion of the relativistic gyration angle has been made, and then higher-order terms up to the third term have been included. Figure 1 shows the comparison of the numerical errors in the momentum and position obtained by RK4, the Boris integrator, the Umeda integrator, and the present method. It is demonstrated that the present method has the fourth-order accuracy in time and is more accurate than the previous integrators. | ||
| 1/23 | Shreedevi PR | Recent advances in modelling the EMIC wave-particle interaction |
| Abstract : Both solar radiation and particle precipitation are important sources for ionizing the upper atmosphere in the high-mid latitude regions. It is commonly accepted that, electrons compared to ions are the major source of energy deposition in the sub- auroral upper atmosphere. However, the origin of localized ion precipitation in the sub-auroral regions and its relative contribution to the total energy flux deposited into the ionosphere is not well understood. Statistical and case studies relate the EMIC wave-particle scattering in the inner magnetosphere to the loss of ring current ions into the ionosphere. We implemented this loss mechanism in a kinetic ring current model (RAM-SCBE) as a diffusion process aided with the associated pitch angle diffusion coefficients. To understand the role of EMIC wave-particle scattering in causing ion precipitation into the ionosphere, we conducted two simulations using the Space Weather Modeling Framework (SWMF) (BATSRUS+RAMSCBE) with and without EMIC waves included. We validated the simulation results by examining the temporal and spatial evolution of the proton precipitation into the ionosphere during the geomagnetic storm of 27-28 May 2017 and its correspondence to the EMIC wave activity observed by the Arase and the RBSP-A satellite. Results indicate that the RAM-SCBE model is able to capture the EMIC wave activity fairly well. The simulation with EMIC waves reproduces the precipitating fluxes in the premidnight sector, and is found to be in good agreement with the DMSP and MetOp satellite observations. The results suggest that the EMIC wave scattering of ring current ions gives rise to the proton precipitation in the premidnight sector at subauroral latitudes during the main phase of the 27 May 2017 storm. | ||
| 1/20 | Akari Nagatani | Time variations of molecular ions in the inner magnetosphere observed by Arase |
| Abstract : Molecular ions in the magnetosphere are originated in the Earth’s ionosphere. Using the data from the Arase MEPi instrument, variations of molecular ions to magnetic storms and solar wind conditions have been investigated, and molecular ions are observed in the inner magnetosphere even during small magnetic storms [Seki+, 2019]. However, observations about molecular ions are still not enough compared with other ion observations, and the mechanism of the outflow from the ionosphere as well as the long-term variations are not well known. In this study, we analyzed the time-of-flight (TOF) data from LEPi [Asamura+, 2018] onboard Arase from April 2017 to July 2022 to investigate variations of molecular ions in the inner magnetosphere and their dependence about magnetic activities and solar wind conditions. LEPi covers the energy range from 10 eV/q to 25 keV/q and counts as function of energy and TOF are obtained every 16 seconds. The TOF measurements of LEPi have been operated in the outbound pass every four revolutions around the Earth. In the analysis, we estimate counts of molecular ions by fitting the empirical functions on the TOF profile using the non-linear least squares method. The estimated counts are calibrated by the time variations of efficiency of the LEPi instrument. The long-term variations associated with the solar cycle are found. Comparing the counts between 2020 and 2022, the average count increases 2.73 times. Besides long-term variations, the molecular ion counts increase associated with the magnetic storms and solar wind speed. The average counts of the molecular ions during non-storm time in 2022 are larger than the severe magnetic storms in 2019/2020, suggesting that the molecular ions in the magnetosphere largely depend on the solar cycle, i.e., solar-UV conditions. | ||
| 1/16 | Harune Sekido | Improvement of the Electromagnetic Simulation and Application to the Magnetohydrodynamics Simulation |
| Abstract : The Finite-Difference Time-Domain (FDTD) method (Yee 1966) is a numerical method for solving the time development of electromagnetic fields by approximating Maxwell's equations in both space and time with the finite difference of the second-order accuracy. A higher-order version of the FDTD method is known as FDTD(2,4), which uses the finite difference of the fourth-order spatial difference (Petropoulos 1994). A new explicit and non-dissipative FDTD method in two and three dimensions is proposed for reduction of anisotropy in numerical dispersion and relaxation of the Courant condition. The third-degree difference terms including Laplacian are added with coefficients to the time-development equations of FDTD(2,4). Optimal coefficients are obtained by a brute- force search of the dispersion relations, which reduces phase velocity errors but satisfies the numerical stability as well. The new method is stable with large Courant numbers where the conventional FDTD methods are unstable. The new method also has smaller numerical errors in the phase velocity than conventional FDTD methods. | ||
| 1/13 | Ichiro Goto | How to discriminate active regions producing eruptive flares and confined flares |
| Abstract :
Corona Mass Ejections (CMEs) are the massive eruption of solar coronal plasma into interplanetary space. CMEs may affect geospace and interplanetary space. It is essential for space weather forecasting to predict when CME occurs. Some CMEs are associated with flares, but some CMEs are not. So we must predict which AR will produce an eruptive flare (flare with CME) or confined flare (only flare). Many studies have been conducted for that purpose. But the predictability of CMEs is still preliminary. Recently, Liu et al. (2022) suggested that the averaged force-free parameter alpha tends to behave differently in the preflare phase between active regions producing eruptive and confined flares. The force-free parameter alpha is calculated by
α=[∇×B]z/Bz, where Bz and [∇×B]z are the normal components of the magnetic field and the curl of it on the solar surface. They suggested that the average alpha decreases before an eruptive flare but does not change well for a confined flare. However, the reason for the decrease in alpha is not apparent. Here, we address some hypotheses to explain the different behavior of the averaged alpha to find the characteristic features of active regions producing eruptive and confined flares. I will pose the research plan to evaluate the proposed hypotheses and show the preliminary results. |
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| 12/23 | Keitaro Matsumoto | Study of acceleration and propagation process of high-energy electrons based on radio imaging observations in a solar flare |
| Abstract :
In this study, we investigated in detail the acceleration and
propagation processes of electrons by combining multi-wavelength
observations and numerical analysis, focusing on non-thermal microwave
radiation during solar flare events. The analysis of the microwave
fast propagation phenomenon described below reveals the pitch angle
distribution of electrons and provides restrictions on the
acceleration mechanism.
Many particles are accelerated in solar flares. The pitch angle distribution of particles is necessary to understand the process of acceleration and propagation of solar flares. The pitch angle of accelerated electrons is estimated from the propagation velocity of non-thermal microwave sources recorded in the Nobeyama radioheliograph. We found another event (M-class flare on October 22, 2014) that indicates fast propagation of nonthermal microwave sources. The propagation from the loop top region to the footpoint was observed based on the loop structure observed by the Advanced Imager onboard the Solar Dynamics Observatory (SDO) satellite. Using the coronal magnetic field model, the velocity of the accelerated electrons parallel to the magnetic field was approximated as 98,000 km/s. The weak microwave feature following the first propagation is interpreted as a second propagation caused by the bouncing motion of the accelerated electrons. Assuming bouncing motion, the velocity along the loop is about 110,000 km/s, which is roughly consistent with the velocity obtained from the first propagation from the top of the loop. The estimated pitch angle of the accelerated electrons is 60° and the size of the loss cone (estimated from the strength of the magnetic field in the coronal field model) is about 36°. Most of the accelerated electrons are estimated to be reflected in the footpoint region. Acceleration trapped in flare loops This is the first observation of bounce motion of electrons trapped in a flare loop. Moreover, we did some simulations about the microwave radiation in this flare. The Fokker-Planck equation is solved for the phase space density with pitch angle and energy as independent variables, and the time variation of 17 GHz microwave emission along the loop is calculated. The results suggest that the electron injection occurred in the direction of the footpoint on one side, compared to the observation. Furthermore, we conducted a parameter survey of the injection position and pitch angle distribution of the accelerated electrons using this method, and compared the results with the observations. We discuss the injection of accelerated electrons in this event. |
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| 12/9 | Sandeep Kumar | Plasma pressure distribution of ions and electrons in the inner magnetosphere during CIR and CME driven storms observed by Arase satellite |
| Abstract : Geomagnetic storms are the main component of space weather, and the main phase of the geomagnetic storms are driven by Coronal Mass Ejections (CMEs) or Corotating Interaction Regions (CIRs). It is well known that CME-driven storms and CIR-driven storms have different evolutions of the Sym-H and the ion distributions in the inner magnetosphere [Miyoshi and Kataoka, 2005]. Enhancement of the ring current is a typical feature of the geomagnetic storm and a global decrease in the H component of the geomagnetic field is observed during the main phase of the geomagnetic storm. The ring current represents a diamagnetic current driven by the plasma pressure in the inner magnetosphere. The plasma pressure is mainly contributed by protons in an energy range of a few to a few hundreds of keVs. The O+ contribution is also important, and sometimes dominates H+ during the geomagnetically active period. However, the contribution of electron to the ring current is not well understood. Recently, we showed that the electron pressure also contributes to the depression of ground magnetic field during the November 2017 CIR-driven storm by comparing Ring current Atmosphere interactions Model with Self Consistent magnetic field (RAM-SCB) simulation, Arase in-situ plasma/particle data, and ground-based magnetometer data [Kumar et al., 2021]. Arase observed 26 CIR originated geomagnetic storms during 2017-2021. In this study, we examine statistically the spatial and temporal distribution of electrons and ions pressure with different energies and their contribution to the depression of the magnetic field during main phase, early recovery and late recovery phase for selected CIR storms using in situ plasma/particle data obtained by Arase. | ||
| 12/2 | Masaya Yakura | Evolution of the electron acceleration site in solar flares using Time-of-Flight analysis |
| Abstract : It is well known that a large number of particles are accelerated during a solar flare. However, the particle acceleration process has not been clearly revealed yet. As for the acceleration site, there are few observational studies since it is difficult to identify directly it from imaging observations. The most outstanding study was done by Aschwanden et al. (1996) using the so-called Time-of-Flight (ToF) analysis technique. They concluded that the electron acceleration site is located slightly above the flare loop. Although the time evolution of the acceleration site during a flare is important for understanding the acceleration process, there are no studies about this topic. In this situation, we try to obtain new information on the evolution of the acceleration site using high-time resolution X-ray data derived by the Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope. To investigate the time evolution of the acceleration site, ToF analysis was applied for each of the time-windows including an outstanding spike appeared in the hard X-ray light curve for a flare occurring on 25 June 2015. Then, a time series of time-lags between different energy ranges were derived. That showed that the ToF distance is larger in the later phase of the flare. This means that the acceleration site moved upward during the flare. However, the magnetic field structure of this flare is too complicated to interpret this result. Thus, another flare was analyzed to confirm this result. In this seminar, the initial result of this analysis is also introduced. | ||
| 11/25 | Ryouta Ikeba | Computer simulation on the structure of double layer in the auroral acceleration region |
| Abstract : The existence of electric fields in the auroral region was predicted by Alfven (1957). Rocket observations of aurora in 1960's showed the precipitation of high energy electrons, possible due to electric fields in the acceleration region (McIlwain 1960). Evans (1974) reproduced the result of rocket observation by a model calculation, which demonstrated the existence of the auroral acceleration region. Electric fields due to the electric double layers in the auroral acceleration region were first observed by spacecrafts in 1970's (Mozer et al. 1977). The FAST observation showed detailed multi-dimensional structures of the auroral double layer (Ergun et al. 2001). The previous one-dimensional Vlasov-Poisson simulation of a current-carrying plasma showed that a double layer was generated by a strong density depression (Newman et al. 2001). However, multi-dimensional kinetic simulations have not been performed yet due to both computational resources and computational techniques. In the present study, we first perform a two-dimensional particle-in-cell simulation of a current- carrying plasma with a density depression. It is demonstrated that a double layer is driven generated in the two-dimensional system with a weak ambient magnetic field. An electrostatic wave is excited inside the double layer at the frequency around the ion plasma frequency and at the phase velocity around the ion acoustic speed, which propagates in the direction oblique to the ambient magneto field. | ||
| 11/11 | Kazuteru Takahashi | Darkening of the pulsating aurora by large amplitude chorus waves: code-coupling simulation |
| Abstract : The Pulsating aurora is a type of diffuse aurora, and pulsation periods are several seconds -several tens of seconds. The amplitudes of the optical emissions should be proportional to the downward energy flux inside the loss cone, so it is natural to consider that that optical emission increases when the wave amplitudes increase if we consider the quasi-liner process. Recent observations indicated that the non-linear wave-particle interactions are essential to cause the pulsating aurora, and it is expected that the relationship between the optical emissions and wave amplitude is not simple as expected from the quasi-linear theory. For example, the phase-trapping effect may suppress the precipitation flux if the wave amplitudes increase. In order to investigate how the precipitation flux changes with the wave amplitudes, we conduct a test-particle simulation about chorus wave-particle interactions using GEMSIS-RBW (Saito+, 2012). Besides non-linear wave-particle interaction processes, stochastic differential equations that is equivalent to the Fokker-Planck equation are included to realize stable precipitations as like the quasi-linear process. Using the simulated precipitating electron flux from the test-particle simulation, we calculate the optical emissions at different wavelength at the ionospheric altitudes. From the simulations, we found that both the intermittent precipitations by chorus wave particle interactions and steady precipitations by quasi-linear process are suppressed when chorus amplitude increases, which are not expected from the quasi-linear process. | ||
| 10/28 | Hotaka Tsujimura | Probabilistic prediction of solar wind speed variation with solar cycle activity |
| Abstract : As the solar wind continues to blow toward the earth, there are concerns about communication problems and the impact on power transmission facilities. Prediction of the solar wind is important to avoid such risks. It is empirically known that the speed of the solar wind is determined by the ratio of the magnetic field of the solar surface to the magnetic field of the solar wind. (The Wang-Sheeley-Arge model (WSA model) is an empirical expression of this relationship.) Therefore, if we can reproduce the magnetic fields at these two locations, we can predict the velocity of the solar wind. The SFT model consists of an advection term, a magnetic diffusion term, and a magnetic flux appearance term. The flux appearance term requires information on the number, latitude, longitude, and tilt angle of the sunspots that appear. However, these parameters that characterize sunspots are generally statistically indeterminate, and we don’t have a good understanding of how this statistical variability affects the solar surface magnetic field and solar wind speed. In this study, solar wind speeds were predicted using these three models. Among them, we predicted solar wind speed variations by stochastically varying the input parameters of the SFT model: sunspot number, tilt angle, emergence latitude, and emergence longitude. As a result, the probability distribution of solar wind speed was obtained to determine how much the solar wind speed could vary over an 11-year period. In this article, we will discuss the results of our discussion on solar wind variability in solar cycle 25 based on these results. | ||
| 10/21 | Yeongmin Kang | Long-term Data-driven MHD Simulation of M5.3 flare event in AR 11283 |
| Abstract : Solar eruptive events such as solar flares are caused by the release of magnetic energy accumulated in the solar atmosphere. To understand the physical mechanism of solar flares, the dynamics of magnetic fields in the solar corona must be studied. Unfortunately, the dominant mechanisms are still unclear due to lack of information about coronal magnetic fields. Numerical simulations based on magnetohydrodynamics (MHD) reproducing the dynamical evolution of solar corona can be a useful method to explore flare initiation. One approach to explore different mechanisms is a data-driven MHD simulation in which the time-series observational data of the photospheric magnetic field can be used as input data. We used a data-driven model (Kaneko et al. 2021) in which the time-series data of the observational photospheric magnetic field was introduced to the bottom boundary. The target of our simulation was solar active region 11283 (AR 11283) where several large flares occurred successively. The simulation was governed by zero-beta MHD, focusing on the long-term period from the formation of the highly-twisted flux rope to the M5.3 flare whose peak time was 2011 Sep, 6 01:59 UT. The simulation covered the period from 2011 Sep, 4 19:48 UT to Sep, 6 06:48 UT. We reproduced both the flux rope formation and the following eruptive event, both of which were consistent with observations. Moreover, we conducted the analysis for the possibility of the growth of MHD instability to explain the eruptive direction of M5.3 flare by introducing a new method to evaluate the decay index for MHD (torus) instability. | ||
| 10/14 | Inchun Park | Seed population of relativistic energy electrons in outer radiation belt observed by ARASE satellite |
| Abstract : Relativistic electron populations in the outer radiation belt exhibit a dynamic behavior that influences the space weather. The high-energy electrons are known to originate from external injections and local acceleration. Recent spacecraft missions to the radiation belts analyzed the dynamics of these electrons and studied the origins of various populations. Phase Space Density (PSD) analysis has been widely employed in past years to determine the external or local origin of the electrons. In this seminar, I will present an analysis of the local acceleration of high-energy electrons from the seed population during magnetic storms that is based on the ARASE spacecraft data. | ||
| 10/7 | Yumi Bamba | Investigation of spatiotemporal evolution of erupted solar magnetic flux rope in the inner heliosphere using multi-point spacecraft measurements |
| Abstract : The global structure of the magnetic flux rope embedded in the coronal mass ejection (CME) plays a key role in triggering geomagnetic storms and their cascade of effects. It is thus important to understand how the magnetic flux rope that erupts from the Sun evolves spatially and temporally as it propagates in the inner heliosphere. We reconstructed the global geometrical configuration through the 1D (or 2D) cylindrical fitting on solar eruptive magnetic flux rope events observed by multiple spacecraft including BepiColombo (0.33AU), Solar Orbiter (0.68AU), STEREO-A (0.96AU), and Advanced Composition Explorer (ACE, 1AU) in October 2021. We also analyzed the source region of the flux rope eruption on the solar surface observed by Solar Dynamics Observatory (SDO). Based on the analysis results, we discuss the radial evolution of the magnetic flux rope, i.e., from that formed and erupted on the solar surface to that propagating through the inner heliosphere. | ||
| 9/30 | Takayuki Umeda | Multi-color reordering for computing moments in particle-in-cell plasma simulation |
| Abstract : Thread parallelism in the computation of the current density/charge density in particle-in-cell plasma simulations has been performed by using the reduction operation conventionally, which is known to have a larger computational overhead with a larger number of threads. In the present study, two types of multicolor reordering, i.e., loop striding and loop tiling/blocking are introduced for a particle shape function with an arbitrary degree, which is free from the reduction operation. The present performance measurement result suggests that the loop tiling is superior to the loop striding. (Comput. Phys. Commun. Vol.281, 108499, 2022) | ||
| 7/29 | Takuma Matsumoto | The first attempts of SUNRISE III mission |
| Abstract :
Sunrise III is a balloon-borne solar observatory dedicated to the
investigation of the key processes governing the physics of the
magnetic field and the convective plasma flows in the lower solar
atmosphere. These processes are crucial for our understanding of the
magnetic activity of the Sun and of the outward transport of energy to
heat its outer atmosphere and to fuel the eruptions and coronal mass
ejections, i.e. phenomena that also affect the Earth system. The
Sunrise observatory is designed for operation in the stratosphere (at
heights up to 40 km) in order to avoid image degradation due to
turbulence in the Earth’s lower atmosphere and to gain access to the
UV spectral range.
From Apr-2022, Sunrise III observatory was moved to Esrange Space Center near the small northern Swedish town of Kiruna. After all the instrumental tests, Sunrise III had lifted off at 3:44 a.m. (CEST) on 10-Jul-2022. During the flight, still unexplained irregularities occurred that made it necessary to end the mission. The flight of Sunrise III was safely terminated at 9:05 a.m. (CEST). A full investigation will follow. In this talk, I will introduce the Sunrise III mission and related activities in Kiruna before the launch. |
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| 7/24 | Haruhisa IIJIMA | Simulating solar wind from convection zone |
| Abstract :
The physical origin of million-degree coronal plasma and supersonic
solar wind has been actively investigated over the past decades. The
common beliefs were established in the theoretical viewpoint: (1)
Thermal convection is a direct energy source of the solar atmosphere.
(2) MHD energy in the corona and wind is transported by the Alfven
wave. (3) The dissipation of the Alfven wave heats the coronal plasma.
(4) The wave pressure of the Alfven wave accelerates the solar wind,
in addition to the gas pressure. However, lots of topics are still
under debate, e.g., (1) observational verification of the above common
beliefs, (2) role of acoustic waves, (3) frequency range of
energy-carrying Alfven waves, (4) role of magnetic flux circulation,
(5) excitation of Alfven and acoustic waves, (6) connection between
the solar surface and solar wind, and others. As only less than 1
percent of convective energy is used for coronal heating and wind
acceleration, these topics should be examined with high
quantitativeness.
We focus on the two barriers to solving this long-standing problem: (1) the three-dimensionality of the magnetic field and (2) the nonlinearity of MHD wave excitation. These barriers prevent the detailed understanding of solar energetics not only in theoretical studies but in observational studies. In the numerical simulation of the solar atmosphere, both the two barriers can be eliminated by including the thermal convection in the upper convection zone. Thanks to the recent advancement of computational resources and numerical techniques, we have succeeded in the first comprehensive 3D radiative magnetohydrodynamic simulation of solar wind acceleration, consistently solving the thermal convection. Simulated thermal convection injects MHD wave energy into the solar atmosphere through the dynamo action and MHD wave excitation. As a result, the one MK corona and supersonic wind are reproduced, with minimal assumptions as possible. We hope this work will help to obtain a more detailed understanding of the solar atmosphere. |
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| 7/15 | Masafumi Shoji | Statistical analyses on low energy ion heating by EMIC waves via wave-particle interaction analyses: Arase observations |
| Abstract : Electromagnetic ion cyclotron (EMIC) waves are generated through the cyclotron wave-particle interaction, affecting the plasma environment in the magnetosphere. Heating of the ions by EMIC waves in the inner magnetosphere has also been investigated by spacecraft observations by comparing variations of ion distribution and waves. The energy transfer between the plasma waves and ions can be quantitatively evaluated by calculating the inner product between the wave electric field vector and the ion velocity vector, so-called WPIA (wave-particle interaction analysis). We adapt the WPIA method to the Arase spacecraft data and investigate the spatial distribution of the positive qV・E region in the inner magnetosphere. Using 4.5 years data, we choose EMIC wave events associating ion flux enhancement between 10 eV to 100 eV of which the WPIA analysis can be applied for the necessary data sets observed by the Arase satellite. The occurrence peaks of the proton and helium heating events appear in the dayside and post noon regions. We classify the enhancements of low energy ion flux by their formation mechanism. Most of the ion flux enhancements are generated through the ion heating by the EMIC waves while some others are formed by the sloshing motion of the ions. | ||
| 7/1 | Chae-Woo Jun | The characteristics of energetic plasma in the inner magnetosphere |
| Abstract :
The Earth’s inner magnetosphere consists of various plasma
populations, and plasma dynamics in this region are mainly controlled
by the electric and magnetic fields. The interaction with energetic
plasma becomes the source of the dynamic phenomena in the inner
magnetosphere, such as the dynamics of magnetospheric waves in the
radiation belts. The plasma configurations in the inner magnetosphere
are mainly classified by their temperature and density. The
plasmasphere has the densest (> 100 cm-3) and coldest (< 1 eV) plasma
configuration near the earth (1-4 Re). The ring current region shows
torus-like structures where the energy density of the plasma is the
highest in the inner magnetosphere. The Van Allen radiation belts
consist of energetic particles of electrons and ions within more than
a few hundred keV, and they are well known to be very harmful to human
beings and artificial satellites.
In this talk, we would like to introduce how inner magnetospheric plasma varies due to the various geomagnetic phenomena. We also present our recent results of the plasma distributions in the inner magnetosphere observed by the Arase satellite in 2017-2021. |
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| 6/24 | Haruhisa IIJIMA | Simulating solar wind from convection zone |
| Abstract :
The physical origin of million-degree coronal plasma and supersonic
solar wind has been actively investigated over the past decades. The
common beliefs were established in the theoretical viewpoint: (1)
Thermal convection is a direct energy source of the solar atmosphere.
(2) MHD energy in the corona and wind is transported by the Alfven
wave. (3) The dissipation of the Alfven wave heats the coronal plasma.
(4) The wave pressure of the Alfven wave accelerates the solar wind,
in addition to the gas pressure. However, lots of topics are still
under debate, e.g., (1) observational verification of the above common
beliefs, (2) role of acoustic waves, (3) frequency range of
energy-carrying Alfven waves, (4) role of magnetic flux circulation,
(5) excitation of Alfven and acoustic waves, (6) connection between
the solar surface and solar wind, and others. As only less than 1
percent of convective energy is used for coronal heating and wind
acceleration, these topics should be examined with high
quantitativeness.
We focus on the two barriers to solving this long-standing problem: (1) the three-dimensionality of the magnetic field and (2) the nonlinearity of MHD wave excitation. These barriers prevent the detailed understanding of solar energetics not only in theoretical studies but in observational studies. In the numerical simulation of the solar atmosphere, both the two barriers can be eliminated by including the thermal convection in the upper convection zone. Thanks to the recent advancement of computational resources and numerical techniques, we have succeeded in the first comprehensive 3D radiative magnetohydrodynamic simulation of solar wind acceleration, consistently solving the thermal convection. Simulated thermal convection injects MHD wave energy into the solar atmosphere through the dynamo action and MHD wave excitation. As a result, the one MK corona and supersonic wind are reproduced, with minimal assumptions as possible. We hope this work will help to obtain a more detailed understanding of the solar atmosphere. |
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| 6/17 | Hisashi Hayakawa (IAR) | Overviews of the Extreme Space Weather Events in January 1938 and March 1940 |
| Abstract : Solar eruptions can direct interplanetary coronal mass ejections and severely affect the near-Earth space environments and technological infrastructures. These space weather events have been quantitatively measured from the International Geophysical Year (1957-1958) onward on multiple physical aspects. However, the space weather events reportedly have achieved further extremity in a longer time scale and it has been challenging to quantitatively understand these extreme events. Besides the greatest space weather events in the late 19th century, this is also the case with the space weather events in the early 20th century. Here, this presentation shows two case studies for the extreme space weather events in January 1938 and March 1940, on the basis of the contemporary reports for their solar surface, source solar eruptions, solar proton events, ICME impacts, geomagnetic storms, and auroral extension. These results provide scientific basis for further discussions on such extreme consequences and prove feasibility for analyses of the extreme space weather events. | ||
| 6/10 | Tomoaki Hori (CIDAS) | Spatial relationship of subauroral polarization streams (SAPS) and particle boundaries as observed by Arase and SuperDARN |
| Abstract : Relative displacement of subauroral polarization streams (SAPS) and particle boundaries in the inner magnetosphere is extensively investigated using particle and field data obtained by the Arase satellite. The enhancement of electric field is frequently observed around the intermediate region between the ion and electrons plasma sheets (PS) along inner magnetosphere passes of Arase in the evening-to-midnight sector, when SAPS is identified at the ionosphere by Super Dual Auroral Radar Network (SuperDARN). A close examination of the Arase observations reveals that the radially-inner boundary of SAPS electric field can form either in the intermediate region or at a further inward location of the PS gap, the latter cases showing apparent inconsistency with what is expected from the simple current-generator model. The talk discusses possible scenarios that can explain the variety of the spatial relationship of SAPS with both PS, and possibly the plasmapause. | ||
| 6/3 | Yoshiki Hatta | Helio-/astero-seismic inversion to infer internal properties of stars |
| Abstract :
In principle, we cannot see inside stars with any telescopes
because the stellar interiors are opaque.
However, we can observationally infer the stellar interiors
based on measurements of the stellar oscillations (stellar seismology).
Seismology of the Sun (stars) is called helioseismology (asteroseismology).
In this talk, I am going to present a brief review of helio-/astero-seismology. I will especially focus on seismic inversion which plays a central role in inferring the internal properties of stars. How to validate results of seismic inversion will be demonstrated. Then, a few primary results of helio-/asteroseimic inversion, for instance, the internal rotation profiles and internal structures are shown. We will see how significant the seismic inferences are as constraints on theoretical studies of stellar internal structures and dynamics, which is otherwise impossible to do with other astronomical techniques. |
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| 5/20 | Satoko Nakamura | Are geomagnetically induced currents (GICs) really a threat for the Japanese power grid? |
| Abstract :
Geomagnetically induced currents (GICs) are one of the main
manifestations through which
space weather affects human technical facilities, and GICs constitute
the final link in the sun-magnetosphere-ionosphere-ground interaction
chain. The most exposed countries are those at high latitudes where the occurrence of intense GICs has seriously damaged part of their power networks in the past. However, it has been revealed that severe space weather can cause intense GICs also at middle and low latitudes. There have been some confusing questions about the risk against geomagnetic induced current (GIC) as follows; - How geomagnetic disturbances actually drive GIC in power lines? - Does the vulnerability of modern power grids increase or decrease? - Which influence on the system is "really" hazardous? - What is the key factor determining the magnitude of GIC? - How to mitigate the impact of GIC? I review the fundamental knowledge of GIC and present new results simulating the risk of the Japanese power grid against the Carington storm. |
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| 5/13 | Aki Ieda | Oxygen ion-neutral collision for space weather |
| Abstract : Solar flare and auroral breakup ionize the neutral atmosphere of Earth and planets. Generated ions collide with the neutral atmosphere, leading to heating and expansion of the atmosphere, resulting in braking and loss of low-altitude satellites. The atomic oxygen ion-neutral collision is the key for this space weather sequence in Earth, Venus, and Mars. However, there are many models of cross section for this collision, and the cross sections differ from each other by a factor of two. In addition, the valid temperature range of their fit is limited between 300 and 2000 K. It is not widely recognized that this temperature range is often insufficient for ionospheric studies, in particular during strong storms in Earth or during solar minimum in Venus and Mars. We have made a fit using a theoretical basis function that include the attractive polarization force and the quantum fine-structure effect. The resultant fit is valid between 80 and 9000 K. This temperature range is practically sufficient to study ionospheres of Earth, Venus, and Mars, including extreme events. | ||
| 5/6 | Satoshi Masuda | Solar Flare Observations with NoRH and RHESSI |
| Abstract : We review initial results of a statistical study of solar microwave and hard X-ray flares jointly observed over the past two solar cycles mainly by the Nobeyama Radioheliograph (NoRH), and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). As has been previously demonstrated, the microwave (17 GHz and 34 GHz) peak flux shows a linear correlation with the nonthermal hard X-ray bremsstrahlung peak emission seen above 50 keV. The correlation holds for the entire rise phase of each individual burst, while the decay phases tend to show more extended emission at microwaves than is generally attributed to particle trapping. While the correlation is highly significant (coefficient of 0.92) and holds over more than four orders of magnitude, individual flares can be above or below the fitted line by an average factor of about 2. By restricting the flare selection to source morphologies with the radio emission from the top of the flare loop, the correlation tightens significantly, with a correlation coefficient increasing to 0.99 and the scatter reduced to a factor of 1.3. These findings corroborate the assumption that gyrosynchrotron microwave and hard X-ray bremsstrahlung emissions are produced by the same flare-accelerated electron population. | ||
| 4/22 | Yoshizumi Miyoshi | SRelativistic electron microbursts as a high-energy tail of pulsating aurora and and its effects in the atmosphere |
| Abstract : Whistler chorus waves cause energetic electron precipitations into the Earth’s atmosphere, and signatures of precipitations are observed as diffuse, pulsating aurora(PsA), and microbursts of energetic electrons. Last year, we discussed our model about the energy spectrum of precipitating electrons and recent Arase observations confirmed the model. And also, we showed our new model that PsA and relativistic electron microbursts (relativistic energy) are the same product of chorus wave‐particle interactions, and we proposed that relativistic electron microbursts are a high-energy tail of the pulsating aurora electrons, which have been confirmed very recently by coordinated observations between low-altitude satellite and ground-based observations. In this presentation, we present our coordinated observations between Arase and EISCAT that is an incoherent scatter radar to measure the upper/middle atmosphere, and we show that MeV electrons precipitate into the middle atmosphere by chorus wavesa associated with PsA embedded in the omega-band. The computer simulation shows that the precipitated MeV electrons cause a catalytic destruction of mesospheric ozone that may have a great impact on the middle atmosphere. We would also like to present our on-going and future projects to understand a link between magnetosphere and middle atmosphere. | ||
| 4/15 | Kanya Kusano 草野完也 | Study of electron acceleration/propagation process in a solar flare using Nobeyama Radioheliograph |
| Abstract :
The solar-terrestrial environment is a complex system that consists of
nonlinear, non-equilibrium, and multi-scale interacting processes. The
Integrated Studies Division aims to improve our understanding of the
dynamics of various phenomena in the solar-terrestrial environment
through data analyses, numerical simulations, and modelings.
Integrated Studies Seminar plays a vital role in discussing different
research topics of the solar-terrestrial environment with all members
of the division. In the first part of this seminar, I will give a
brief introduction to the integrated studies seminar and explain how
important is the holistic aspect to understand and predict the
dynamics of the solar-terrestrial environment.
In the second part, I will talk about our new research project for the
solar and heliospheric integrated model. Solar explosions, such as
solar flares and coronal mass ejections (CMEs), occur as the
consequence of the destabilization of the coronal magnetic field
generated by the dynamo process inside the sun (convection zone). The
solar explosion may cause space weather disturbance, and thus it is a
potential risk for the infrastructure that supports modern society.
However, research on the inside and outside of the Sun has been
separated so far, and the physics that interconnects the convection
zone, the solar atmosphere, and the interplanetary space has not been
well elucidated. Therefore, the ability to predict solar explosions
and space environmental variation is still insufficient. To overcome
this difficulty, we recently launched a new research project for the
integrated model of the solar and heliospheric system. In this
project, we challenge to develop the integrated model including from
the solar convection zone to interplanetary space. Through this
project, we aim at realizing advanced predictions of solar explosions,
elucidating the cause of the solar cycle and solar flares, and
clarifying the physics that determine the maximum limit of solar
explosions. In this seminar, I will review what we have achieved in
the last year and what are still remaining as our issues. 太陽地球環境は、非線形、非平衡、およびマルチスケール相互作用プロセスが支配する複雑なシステムです。総合解析研究部では、データ分析や数値シミュレーション、モデリングを通じて、太陽地球環境におけるこうした様々な現象のダイナミクスの理解を深めることを目的としています。総合解析セミナーは、太陽地球環境のさまざまな研究トピックについて研究部のすべてのメンバーが議論する重要な役割を果たす場です。この講演ではまず、総合解析セミナーの役割を簡単に説明し、太陽地球環境のダイナミクスを理解し予測するための統合研究がいかに重要であるかを議論します。 後半では、太陽と太陽圏の統合モデルに関する新しい研究プロジェクトについてお話します。太陽フレアやコロナ質量放出（CME）などの太陽面爆発は、太陽内部（対流層）のダイナモプロセスによって生成された磁場が太陽表面とコロナで不安定化する結果として発生します。太陽面爆発はしばしば大規模な宇宙天気擾乱を引き起こす可能性があり、現代社会を支えるインフラストラクチャーにとっても潜在的なリスクです。しかし、これまで、太陽の内部と外部の研究は分断されており、太陽対流層、太陽大気、惑星間空間を相互に結合する物理過程は十分に理解できていません。そのため、太陽面爆発の発生や宇宙環境の変化を予測する能力はまだ不十分です。この困難を克服するために、私たちは太陽・太陽圏システムの統合モデルに関する新しい研究プロジェクトを立ち上げました。このプロジェクトでは、太陽対流層から惑星間空間までを含むモデルの開発に挑戦します。このプロジェクトを通じて、これまで不可能であった太陽面爆発の早期予測を実現すると共に、太陽と恒星の周期活動とフレアの基本性質を説明し、太陽フレアの最大限界を決定するメカニズムを明らかにすることを目指しています。本セミナーでは昨年度のプロジェクトの成果と残されている課題について説明します。 | ||