令和２年度 総合解析セミナー
日時： 金曜 13:30 – 15:00
場所： ZOOM
| date | Speaker | title |
|---|---|---|
| 2/19 | 川崎一賢 | 機械学習を用いた太陽コロナ画像と太陽表面磁場画像の相互変換 |
| Abstract : 機械学習を用いた太陽磁場画像から太陽のUV, EUV画像への変換はこれまでしばしば行われてきた(Park et al,2019, Galvez et al 2019)。Park et alにおいては、機械学習で画像変換を行なった結果良い相関係数となることが示されている。また、Galvez et alでは変換に機械学習を用いる際に訓練データとテストデータを時系列的に混在させるべきでないことが示されている。しかし、訓練データの詳細な設定方法と、それに伴う評価値の変化については検証されてこなかった。加えて、太陽コロナ画像から太陽磁場画像への変換は行われていないため、機械学習を用いて磁場画像を出力する際の特性は解明されていない。本研究では太陽コロナ画像と太陽磁場画像の相互変換を通して、訓練データと評価値の関係や、磁場画像を出力する際の特性に関する研究を行った。 | ||
| 2/19 | 辻村穂高 | 表面磁束輸送モデルを用いたサイクル２５での太陽表面磁場の確率予測 |
| Abstract : 太陽活動が大きくなると、地球へ悪影響を与えることもある。そのためこの活動を観測、予測することは非常に重要なことである。太陽活動を予測するための方法としてSurface Flux Transport Model(SFTモデル)があり、太陽表面の磁場を算出することが出来る。この計算モデルには様々なパラメータが存在しているが、これらのパラメータの変動による結果への影響はまだ解明され尽くしていない。研究では、SFTモデルを用いてサイクル２５においての幅を持った太陽表面磁場を予測した。また、入力する黒点数、tilt angle、子午面循環流を変化させ、そのときの磁場への影響を確かめた。 | ||
| 2/19 | 野村佳槻 | sCMOSカメラデータの解析によるフリッカリングオーロラの輝度変調の性質の研究 |
| Abstract : フリッカリングオーロラはブレークアップ中に現れ、その典型的な周波数は3 Hzから15 Hz程度である。フリッカリングオーロラの発生で考えられている起源の一つとしてで、電磁イオンサイクロトロン波動（EMIC波）が高さ数千kmでの電子のフラックスを変調する過程がと考えられている。本研究では、フリッカリングオーロラは振幅変調があり、背景のオーロラの強度に対して10 %から20 %の変調である。フリッカリングオーロラの振幅変調の詳しい性質を理解するために、アラスカのPoker Flat Research Rangeにおいてあるs-CMOS cameraの分析を行い、特に背景のオーロラ強度が異なる場合のフリッカリングオーロラの振幅の分布に注目した解析を行ったを調べる。2016年２月8日6時40分（UTC）のフリッカリングオーロラを解析した。このとき観測されたしたフリッカリングオーロラの周波数は、約3 Hzから9 Hzであった。また、背景のオーロラアークに対する変調成分の強度比を求めたところ、その平均は13%で、標準偏差10%の正規分布であった。また、この変調成分の背景オーロラに対する発光強度の比は、背景のオーロラの輝度には寄らない結果が得られた。フリッカリングオーロラの輝度変調は、電子の下向きのエネルギーフラックスの変化、すなわち降下電子のエネルギーと降下電子のフラックスに依存する。もしフリッカリングオーロラが、EMICによる電子のランダウ共鳴によって発生している場合には、降下電子のエネルギーの変化はEMICの位相速度の変化を反映する。したがって、本解析の結果は、背景のオーロラアークが、フリッカリングオーロラを起こすEMIC波動の特性を変えている可能性を示唆するものであり、フリッカリングオーロラの発生過程の解明に重要な成果である。 | ||
| 2/12 | 池羽良太 | オーロラ加速領域における電界構造の多次元シミュレーション |
| Abstract : オーロラ加速領域における電気二重層により生じる電界は1970年代にはじめて観測された (Mozer et al. 1977）。FAST 衛星の観測結果はオーロラの電気二重層の多次元構造を示唆し ている（Ergun et al. 2001）。以前の電流を流したプラズマの 1 次元 Vlasov シミュレーショ ンによりプラズマ中の密度降下が電気二重層を引き起こすことが示されている(Ergun et al. 2001)。しかしながら、多次元運動論シミュレーションは計算資源と計算技術の不足のため これまで行われてこなかった。本研究では、オーロラ加速領域における多次元電界構造の再現を行うために電流が流れるプラズマ中に密度降下を与えて2次元 PIC(particle in cell)シミュレーションを初めて行った。 | ||
| 2/12 | 小川逸希 | あらせ衛星搭載飛行時間計測型イオン質量分析器を用いた地球磁気圏低エネルギーイオン組成の研究 |
| Abstract :
地球周辺には地球磁気圏という固有の空間が存在し、そこには太陽風起源によるH+,He+,He++や、地球の電離圏起源によるH+,He+,O+,O++,N2+などが存在する。 これまでにDE1やAMPTE/CHEM衛星、Van Allen Probes衛星などによって地球磁気圏のH+,O+,He+,He++などの重イオンは観測が実現されてきた。しかし、N2+などの分子イオンの供給源や輸送過程についてはわかっていない。また、地球磁気圏におけるイオン種の分布における太陽活動依存性や磁気嵐が発生した際の変化における規則性についても解明されていない。 本研究では、あらせ衛星に搭載されたLEP-i観測器のTOFの観測データの解析手法の開発を行い、分子イオンを含む重イオンの組成比の研究を実施した。あらせ衛星に搭載されたLEP-iによるTOF観測は、高い質量分解能をもちN2+などの分子イオンも観測可能であるため、地球磁気圏のイオン種の分布を観測する事に適した観測データである。本研究では、2017年4月から2020年3月の観測データを用いた解析を行っている。本セミナーでは、TOFデータから、重イオン、分子イオンの導出方法および検出された各種イオンの変化について報告する。 |
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| 2/5 | Yeongmin Kang | Data-driven MHD Simulation of Solar Active Region |
| Abstract : Solar eruptive events such as flares, coronal mass ejections (CMEs) or prominence eruptions are caused by release of magnetic energy accumulated in the solar atmosphere. They occur in the solar active regions (ARs) where the strong magnetic fields are present. Numerical modeling of the coronal magnetic fields is important to develop physics-based prediction methods for the explosive events. Focusing on flare events, not all of the energy accumulated in AR is released with a single flare. It is still difficult to predict the exact value of released energy. Moreover, the physical mechanism to determine the ratio between the released energy and the stored magnetic energy is unclear. MHD simulation is a powerful method to investigate and understand the evolution of the coronal magnetic fields. In this study, we are going to conduct MHD simulation on the data of AR where several flares have occurred. The simulation method is data-driven method in which the time series observational photospheric magnetic field data (HMI vector magnetogram) are used. The dataset is given as data of AR11283 from September 3, 2011 to September 6, 2011 and M class flare and X class flare each occurred once during this period. The final objective of this study is to know about the energy release rate of these two flares and the physical mechanism by which the rate is determined. For now, some simulations that create an initial condition of coronal magnetic field were carried out and a model that is most similar to the observational magnetic field data was found by parameter survey. | ||
| 1/29 | Minami Mori | Simulation study on the structure and propagation of CME |
| Abstract : Coronal mass ejections (CMEs) are the largest eruptive phenomena in the solar system. Plasmas with masses of 10^11 to 10^13 kg are carried in interplanetary space at velocities of a few hundred - thousand km/s and can affect a variety of space weather conditions. It is a serious factor of space weather disturbance. The eruption mechanism of CME is still unclear. Also, the deflection and rotation of CMEs during the passage to the Earth are important factors to determine the geo-effectiveness. We develop a numerical simulation of CME propagation using the magnetohydrodynamic (MHD) model of the inner heliosphere, SUSANOO-CME (Shiota & Kataoka, 2016). In this model, CME has a spheromak-type magnetic field that forms a combination of toroidal and poloidal components inside. Here, we focus on the dependencies of the CME structure on the initial magnetic field inside CME. The background solar wind is assumed to be uniform and has an isotropic magnetic field. We simulated the four different cases in which the toroidal and poloidal components of the CME magnetic field are respectively inverted. Based on the simulation results, we will discuss how the magnetic field inside CME influences the structure and propagation of CME. | ||
| 1/22 | Kaho Kondo | Comparison of empirical and physics-based methods for flare prediction |
| Abstract : Solar flares suddenly emit electromagnetic waves, plasma and energetic particles into the interplanetary space, and causes the space weather disturbances. Therefore, the prediction of solar flares is important to mitigate the space weather impact. For predicting solar flares, various types of empirical methods have been developed so far, and very recently the physics-based prediction of very large solar flares, called the kappa-scheme, has been developed by Kusano et al. (2020). In this study, we conduct a comparative study of empirical and physics-based predictions of solar flares with the aim of developing a new type of solar flare prediction by combining empirical methods and physics-based methods. As the preliminary study, we focus on the Schrijver’s R-parameter (Schrijver 2007), which is given by the unsigned magnetic flux near the polarity inversion line (PIL) of high magnetic gradient, as a typical empirical method. We use the vector magnetic field data of the active region NOAA 12673 observed by the Solar Dynamics Observatory before the onset time of the largest solar flare in the solar cycle 24 (11:48 UT on September 6, 2017), and calculated the unsigned magnetic flux (local magnetic flux) within a circle of radius 2 Mm centered at each point on the PILs. As a result, we found the following features. (1) The local magnetic flux correlates well with the magnetic gradient on PIL. (2) The local magnetic flux was also high at the flaring point predicted accurately by the kappa-scheme. (3) However, there were places where the local magnetic flux was high although flare did not occur. They suggest that the R-parameter is only partially related to the predictors of the kappa-scheme. We discuss the sensitivity of the local magnetic flux and the R-parameter on the observation error using the Monte-Carlo analysis. We consider a new scheme using these results. | ||
| 12/4 | Masafumi Shoji | Statistical analyses on low energy ion heating by electromagnetic ion cyclotron 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 the pitch angle distribution of the ions and the wave emissions. We can directly detect the energy transfer between the plasma waves and the ions via the wave-particle interaction analysis (WPIA) method which calculates the inner product between the wave electric fields and the ion velocities. We adapt the WPIA method to the Arase spacecraft data and investigate the spatial distribution of the positive region in the inner magnetosphere. From March 21st 2017 to September 27th 2019, we select 60 EMIC wave events associating flux enhancement between 10 eV to 100 eV which are suitable dataset for the WPIA method observed by PWE/EFD, MGF, and LEP-i onboard the Arase satellite. The peaks of the proton heating appear in the dayside and post noon regions. Typical EMIC waves inside the plasma plume contribute to the peak in the afternoon sector in both quiet and active times. On the other hand, in the dayside region, the proton heating takes place during quiet times. It suggests that the protons in the region are energized by the EMIC waves generated by the EMIC waves generated by compression of the magnetic field. We also discuss the heavy ion heating. | ||
| 11/27 | Haruhisa Iijima | Effect of morphological asymmetry between leading and following sunspots on the prediction of solar cycle activity |
| Abstract : The morphological asymmetry of leading and following sunspots is a well-known characteristic of the solar surface. In the context of large-scale evolution of the surface magnetic field, the asymmetry has been assumed to have only a negligible effect. Using the surface flux transport model, we show that the morphological asymmetry of leading and following sunspots has a significant impact on the evolution of the large-scale magnetic field on the solar surface. By evaluating the effect of the morphological asymmetry of each bipolar magnetic region (BMR), we observe that the introduction of the asymmetry in the BMR model significantly reduces its contribution to the polar magnetic field, especially for large and high-latitude BMRs. Strongly asymmetric BMRs can even reverse the regular polar field formation. The surface flux transport simulations based on the observed sunspot record shows that the introduction of the morphological asymmetry reduces the root-mean-square difference from the observed axial dipole strength by 30--40 percent. These results indicate that the morphological asymmetry of leading and following sunspots has a significant effect on the solar cycle prediction. | ||
| 11/20 | Tomoaki Hori | Spatial evolution of injected energetic electrons as observed by Arase and Van Allen Probes |
| Abstract : We investigate how drifting energetic electron populations evolve in the inner magnetosphere, using the Arase and Van Allen Probes (RBSP) satellites. Electrons and ions of the plasma sheet origin are energized up to tens to hundreds of keV and abruptly transported on the night side into geosynchronous distance and even further inward during substorms, which is referred to as substorm injection. Then injected electrons drift eastward and disperse along their drift path with azimuthal drift velocities depending on their energies. Although the energy dispersion signature has been well studied with geosynchronous satellite, its two-dimensional evolution, particularly the radial structure of a drifting electron population has not been well examined. A case study on one of the events we have been working on where the three satellites were located on the dawn side shows that Arase (L ~ 7.7, MLT ~ 10h) and RBSP-B (L ~ 5.8, MLT ~ 4h) observed an energy-dispersed electron population nearly at the same time (within a few minutes), despite the large difference in MLT sector. This result strongly suggests that the “drift front” of energetic electrons goes significantly ahead at farther radial distances even if they have started drifting at the same time from the same location in MLT. | ||
| 11/13 | Satoshi Fukuoka | Forecast of energetic electron flux variations at different L-shells using the machine learning |
| Abstract : The relativistic/sub-relativistic electron flux variations often cause serious damage on the satellite operations through the dielectric charging. In order to forecast flux variations of these electrons, various forecast methods based on the physical based simulation and empirical modeling have been developed. For the physics-based simulation, the SUSANOO that operates a code-coupling simulation of heliosphere and radiation belt provides MeV electron flux variations for the next couple of days. For the empirical modeling, the linear prediction filter and the auto-regressive moving average are popular methods, which have been used for the forecast of MeV electrons at geosynchronous Earth orbit (GEO). Recently, the machine learning techniques have widely been used for the space weather forecast, for example, ionospheric variations, the flare prediction, etc. In this study, we have developed the forecast system of relativistic/sub-relativistic electron flux variations based on long short-term memory recurrent neural network (LSTM-RNN). As the training data, we use the solar wind data and energetic electron data observed by Arase/HEP, XEP instruments at different L-shells of the outer belt. Our developed network provides time variations of the energetic electron flux around L=6 using the solar wind data as an input parameter. On the other hand, the network does not reproduce the observed flux variations at L=4, suggesting that other parameters are necessary as input parameters of the network. In this presentation, we will present the initial results of our developed network and discuss effective solar wind parameters to reproduce the observed flux variations at different L-shells. | ||
| 11/6 | Kento Michiwaki | Prediction of sunspot appearance using deep learning |
| Abstract : For space weather study, it is important to estimate the solar activity in near future. Recently, it is believed that the polar magnetic field at the solar minimum is one of the indicators for the next solar activity. Therefore, many studies try to estimate the solar polar magnetic field for the cycle prediction. The temporal variation of the polar magnetic field can be reproduced by using the surface magnetic flux transport calculation model (SFT model). The SFT model consists of advection term due to differential rotation and meridional circulation, magnetic diffusion term, and flux emergence term. The advection and the diffusion coefficients are estimated by modern observations. On the other hand, estimation of future flux emergence is still very difficult. Therefore, estimating when and where the sunspots will be emerge is crucial for cycle prediction study. In this study, we predicted the sunspot number and latitude distribution (butterfly diagram) using CNN (Convolutional Neural Network) which is one of the machine learning technique. Also, using a prediction model, we verified at what timing in the cycle it would be possible to obtain good prediction results. As a result, we were able to reproduce the transition and periodicity of the appearance of sunspots from mid-latitude to low latitude, which is a characteristic of the appearance latitude. Also, although the accuracy of the prediction needs to be improved, we were able to obtain good accuracy for the prediction of cycles with large changes, such as cycle 24. The results of the validation using the training model showed that better predictions were obtained 4 or 5 years after the start of the cycle (near the peak of the cycle). Finally, the peak amplitude of the next solar cycle (cycle 25) is predicted to occur around 2023, and the peak value is predicted to be slightly larger than cycle 24. We are also trying to predict longitude and tilt angle. | ||
| 10/30 | Kohei Toyama | Estimation of precipitating electron energy of pulsating aurora by multiwavelength aurora optical observation |
| Abstract : Pulsating aurora (PsA) is characterized by quasi-periodic intensity modulations with a period of 2-20 s which is known as the main modulation. Electrostatic Cyclotron Harmonic waves and whistler-mode waves are known to cause the pitch angle scattering of energetic electrons in the magnetosphere, and PsA is considered to be generated by the precipitating electrons with energies of several to 100 keV. In particular, whistler-mode chorus waves play a crucial role in the pitch angle scattering of the electrons. The lower-band chorus causes precipitation of electrons more than several keV, and the upper-band chorus causes steady precipitation of less than 1 keV [Miyoshi et al., 2015]. The precipitating electron energy of pulsating aurora may be estimated from the ground-based optical observations. Ono et al. [1993] observed the emission intensities of pulsating auroras at wavelengths of 427.8 and 844.6 nm using photometers, and estimated the energy of the precipitating electrons by combining the ratio of the two emission intensities and the model calculation. However, Ono et al. [1993] conducted observations using the instrument with a narrow field-of-view, and the energy estimation using all-sky imagers has not been performed. In Tromsoe, Norway, several highly-sensitive EMCCD cameras have been operated, which have simultaneously observed the all-sky images of the emission intensity at the two wavelengths (427.8 and 844.6 nm) with a sampling frequency of 10 Hz. In addition, a five-wavelength photometer has also been operative in Tromso. In this study, we investigate the spatio-temporal variations of precipitating electron energy using these EMCCD cameras. The optical data taken from EMCCD cameras have been calibrated by simultaneous measurements with the collocated photometer fixed to look along the magnetic field line. We estimated the precipitating electron energy of the pulsating aurora by comparing the emission intensity ratio of the two emission lines using the all-sky image and the emission intensity calculation results obtained by the GLOW model [Solomon, 2017]. In the presentation, we show the spatio-temporal characteristics of the precipitating electron energy of the pulsating aurora. | ||
| 10/23 | Kengo Matoba | Calculation of solar surface flow using a magnetic element tracking module |
| Abstract :
Solar flares have impacts on the Earth’s environment. Flares are now believed to be associated with sunspot’s activities. Therefore the 11-year variability in sunspot numbers is one of the major origins of the decadal variability in the solar environment. Predicting sunspot number in next solar cycle is very important for space weather. Building the next solar cycle prediction scheme is the key to long-term space weather research. Recently, it is believed that the polar magnetic field during the minimum period is one of the good indicator for the next solar cycle activity. Surface flux transport (SFT) models are often used to estimate polar magnetic fields. On the other hand, the SFT model requires several parameters, such as meridional circulation, rotational difference, and turbulent diffusion. These parameters are not fully understood, and especially their temporal variation and polar region are still unclear.
In this study, we focused on two typical solar surface flows, differential rotation and meridional circulation. We apply a magnetic element tracking (MET) module to SDO/HMI and Hinode/SOT to obtain solar surface velocities. When applying to HMI, we calculated solar surface flow using ten years data. The other hand, when applying to SOT, we are calculating solar surface flow of polar region. As a result, we obtain the latitudinal profile of the meridional flow and differential rotation speed. We also studied the temporal variations of the meridional flow and differential rotation speed in cycle 24. We find that the differential rotation/meridional flow speed is faster/slower at the latitude where the sunspots frequently emerge, respectively. About using SOT data, we are studying now. So we will introduce how to approach it |
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| 10/16 | Toshinori Matsushita | Design of a 2-Dimensional Phased Array Antenna for IPS Observations |
| Abstract : Interplanetary scintillation (IPS) have been discovered as the scattering phenomena of the radio sources caused by density variations of the solar wind [Hewish, Scott, and Wills, 1964]. IPS data is an important tool for observing the solar wind. We have a radio telescope system operated at 327 MHz for IPS observations which is consist of the three observatory which are located at Toyokawa, Kiso and Fuji. A higher sensitivity receiver system and multi-observation for two or more radio sources at a same time is required to obtain a more accurate synoptic map of solar wind parameters. We have been developing a 2-dimensional phased array antenna system for satisfaction of these requirement. This detail design of the phased antenna must account for mutual effects because the array factor method included no mutual effects is not enough accuracy for a gain and directivity. We have applied a Network theory model included mutual effects, designing a 2-dimensional phased antenna. We will present an interim report about the designing of a 2-dimensional phased array antenna and the progress. | ||
| 10/9 | Pei-Hsuan Lin | New Schemes to Distinguish Eruptive-Flare Producing Solar Active Regions Based on of Photospheric Magnetic Field |
| Abstract : Statistical analysis based on linear discriminant function analysis is performed to answer the question of what determines the capability of a solar active region (AR) to specifically produce eruptive flares and coronal mass ejections (CMEs). Based on data obtained by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, the coronal magnetic field for 51 flares larger than M5.0 class, from 29 distinct ARs, is constructed using a nonlinear force-free field extrapolation model. First, the parameter r_m is proposed to measure the possibility that a flare that occurs in an AR can be eruptive and produce a CME. r_m is defined by the ratio of the magnetic flux of twist higher than a threshold T_c to the surrounding—and specifically, the overlying—magnetic flux. It is shown that r_m is moderately well able to distinguish ARs have the capability of producing eruptive flares (vs. confined flares), where field lines that overlie and “fence in” the highly twisted region work to confine the eruption, generating the confined flares. Secondly, to understand why r_m failed to correctly determine the eruptivities of three flares originating from AR 12192, two new schemes of identifying those field lines involved in eruptions, the r-scheme and q-scheme, are proposed based on different identifying strategies. In the r-scheme, the “magnetic twist flux” is introduced to approximate the force balance acting on the magnetic flux rope (MFR). In the q-scheme, the reconnected field is represented by those field lines which anchor in the flare ribbons. The results reveal that despite both schemes providing moderately successful classifications for the 51 flares, the classification for the three target events can only be improved with the q-scheme. Among the target events, the highly twisted field lines and the flare-ribbon field lines are found to have equal values of the average force-free constant α, implying that it is challenging to decouple the MFR from the ambient magnetic field using any measurement based on common measures of magnetic nonpotentiality. | ||
| 10/2 | Inchun Parki | The long-term verification of the calibration result of ARASE/HEP data and statistical analysis of magnetic storm period using calibrated data |
| Abstract : The Arase satellite has been observing high-energy radiation-belt electrons since March 2017 with the high-energy electron experiments (HEP) instrument. The HEP instrument can observe the energy of the electrons from 70 keV to 2 MeV with high spectral and spatial resolution. To collect reliable data, we calibrated the data using Monte-Carlo particle simulation through the Geant4 tool kit. Using the simulation result, We successfully calibrated and verified the observation data by comparing it with the MEP-e instrument observation which overlapped the observation energy band. Thanks to the calibration experience, we developed a simulation toolkit that reconstructing complicated geometry instruments. Using the calibrated data, we have analyzed observation data of 29 magnetic storms. Acceleration and loss energy of a high-energy electron in the Earth magnetosphere during a disturbing period need to explain its process. Recent studies suggest that wave-particle interaction has a major role in the energy exchange process in the sub-MeV to the MeV energy band. We approach this topic from the spectrum and the pitch angle changes. From the analysis result, We confirmed that there is energy dependency in which higher energy has a delayed response from the main phase starts. The pitch angle distribution also has energy dependency. These results help us understand how the growth rate of chorus waves is affected and how the wave-particle interaction occurs. | ||
| 9/25 | Kyohei Murakami | Hall MHD calculation of magnetic reconnection assuming coronal heating |
| Abstract :
Solar corona is hotter than the sun's surface, and its heat source has not been clarified. Even if 1 % of the convective energy on the solar surface is dissipated, it can be explained, but the mechanism is unclear. One of the model for explaining coronal heating is the dissipation of energy by nanoflares. Hinode satellite observations confirm nanoflares between two sun spots. However, it is difficult to observe the structure of the magnetic field lines on the nanoflare scale due to the performance of the Hinode satellite. S. Imada et al (2012) proposed a model in which coronas are heated periodically as a result of the generation of large amounts of nanoflares in the magnetic loop. However, in this model, only one-dimensional fluid calculation is performed, and magnetic reconnection is not reproduced. It was proposed by J. Birn et al (2001) that collisionless magnetic reconnection is accelerated by the Hall effect when the current sheet scale is comparable to the ion inertial length. When twisted magnetic field lines generated inside the sun float on the surface, the density around the current sheet decreases rapidly, so that the ion inertia length increases. This is considered to cause Hall reconnection.
In this study, creating a model in which magnetic reconnection occurs when flux emergence occurs due to the Hall effect. In order to easily reproduce the flux emergence, a gravity term was added horizontally to the current sheet. This represents the gravity along the magnetic loop when flux emergence occurs. Simulates gravitational stratification along the loop and reproduces the situation where the density of the levitated magnetic loop decreases in the corona. In an ideal MHD (no resistance), no reconnection occurs. However, in the calculation that added gravity to the ideal MHD, reconnection occurred. This was numerically dissipated as the density of the current sheet decreased and the current sheet became thinner due to the effect of gravity. However, in the actual corona, it is not a numerical dissipation, but it is thought that magnetic reconnection occurs due to the Hall effect because the plasma density decreases with flux emergence. Therefore, by adding the Hall effect to the code that takes gravitational stratification into account, we confirm that magnetic reconnection occurs when the current sheet thickness is comparable to the ion inertia length |
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| 9/18 | Yoshiki Ito | Computer simulations of precipitating energetic electrons through chorus-wave particle interactions |
| Abstract : Whistler mode chorus waves cause scattering and acceleration of energetic electrons in the inner magnetosphere, and recent studies identified that chorus waves cause the pulsating aurora. The interaction processes have been modeled as diffusions in the velocity space, and it has been supposed that the scattering rate increases with increasing the wave amplitude. However, the wave-particle interactions with chorus waves are non-linear process, so that it is expected that the scattering rate does not simply depend on the wave amplitude. In this study, we investigate chorus wave amplitude dependence of electron scattering using the GEMSIS-RBW simulation code. The GEMSIS-RBW simulation calculates variations of local pitch angle and energy of each test particle by the imposed chorus waves. In this simulation, chorus bursts that consist of multi rising tone elements are imposed at the equatorial plane, and these waves propagate along the field line with L= 4 by calculating the Maxwell equations. We calculate the trajectory of a number of electrons with initial energy of 50 keV and evaluated the number of precipitating electrons with various wave amplitudes. In order to evaluate the number of precipitating electrons that depends on the wave amplitudes, we discriminate betweenresonant and non-resonant electron population. The number of the precipitating electrons through resonance simply increases when the wave amplitude increases from 10 pT to ~200 pT. However, as the wave amplitude increases more than 200 pT, the number of precipitating electrons decreases. From the analysis on the electron motion in the phase space as well as the parameter ρ [Bortnick et al., 2008] that is a proxy of the ratio of the wave-induced and the background inhomogeneity effects for the momentum change of the resonant electron, the phase trapping effect decreases the precipitating flux in the large amplitudes.On the other hand, the number of precipitating electrons through non-resonance increase, , indicating that non-resonant interactions contribute to the total number of precipitating electrons. | ||
| 9/11 | Shoma Uneme | Inference of magnetic field during Dalton Minimum |
| Abstract : Solar activity changes periodically in 11 years. Because the solar activity is one of the main origins of the variability of the solar-terrestrial environment, it is important to predict the solar activity especially in the category of space weather study. It is known that the polar magnetic field at the solar minimum is closely correlated with the solar activity at the next solar activity. This correlation was confirmed by observing the current sun precisely. On the other hand, it is not clear whether there was a similar correlation in the past sun. Therefore, the aim of this study is to analyze the past sun spot sketch images to verify whether the polar field value at the solar minimum is also good correlation with the next solar activity. Especially, we focused on the Dalton minimum when sunspots were little in the early 1800s. We extracted latitude and longitude of sunspot from sketches in the early 1800 's. We will discuss the differences between the result obtained in this analysis and the characteristics of current sun. And next, so as to calculate the surface magnetic flux transport model based on obtained sunspot information and estimate the value of the polar magnetic field at the solar minimum of the Dalton minimum, we tried to generate magnetograms from sunspot drawings in Dalton minimum by cGAN, which is a popular deep learning method, in cooperation with the laboratory at kyung hee Univ. Currently, we are trying to slightly convert the distribution of generated magnetograms and calculate SFT as the evaluation step. | ||
| 9/4 | Yoshizumi Miyoshi | Comparative study on chorus waves and energetic electron variations during a CIR-driven magnetic storm: Arase observations and RAM-SCB and electron hybrid simulations |
| Abstract : During CIR-driven storms, a series of substorms occur associated with Alfvenic fluctuations of IMF and high-speed solar wind. During the period, continuous enhancements of chorus waves are observed due to enhancement of tens keV electron flux from the plasma sheet and decrease of thermal plasma densities. In this study, we simulate dynamics of the energetic electron distributions and the plasmasphere with the RAM-SCB simulation that calculates evolution of the electron distribution function and density of the thermal plasma with self-consistent magnetic field. We compare the simulated electron flux and thermal plasma density along the Arase satellite orbit and the electron flux data as well as the thermal density observed by Arase electron instruments LEPe/MEPe/HEP/XEP and plasma wave instrument PWE/HFA. The RAM-SCB simulation reproduces successfully the observed variations of energetic electrons, for example, injections and subsequent energy dispersion of electrons. Using the simulated distribution functions and the ambient density and magnetic fields, we also calculate the linear-growth rate of whistler mode waves and compare with the Arase plasma wave observation data. The spatial-temporal variations of the linear-growth rate are not always consistent with the observations, so that assessment of non-linear wave growth is necessary. We conduct a code-coupling simulation that consists of RAM-SCB and the self-consistent electron hybrid simulation. We compare the simulation with the wave-burst mode data from Arase/PWE/WFC and discuss what plasma conditions produce the non-linear evolutions of chorus waves. | ||
| 7/17 | Ieda Akimasa | Ion-neutral collisions |
| Abstract : The ion-neutral collision occurs between ions and neutral particles, such as H+ and H. This collision exists in the partially ionized atmosphere, such as the solar chromosphere and the planetary ionosphere. This collision governs the ionosphere. This collision may be crucial for the coronal heating estimation because the Alfven waves dissipate in the chromosphere. In this talk, phenomenology is not further discussed. I will first confirm the basic physics of the ion-neutral collision, including the definition of collision frequency. Then I focus on the misinterpretations of the classic theory by ionospheric studies, as the first step of my series of studies as follows. Molecular oxygen collides with its first positive ion in the earth’s ionosphere. The collision frequency of this particle pair is used to calculate the electric conductivity of the ionosphere. However, for this parental pair there are two collision types, resonant and nonresonant, and the selection of the collision type has differed among previous studies in calculation of conductivity. In the present study, we clarify that the nonresonant collision is physically essential for this pair because the relevant temperatures are low. That is, the peak of the ionospheric conductivity occurs at altitudes between 100 and 130 km, where the temperatures of ions and neutral particles are usually lower than 600 K, and for these temperatures nonresonant collisions are dominant. The collision frequency would be underestimated by 30% if the resonant collision was assumed at an altitude of 110 km (where the temperature is 240 K). The impact of this difference on the conductivity is estimated to be small (3%), primarily because molecular nitrogen is much more abundant than molecular oxygen. Although we have confirmed that the nonresonant collision is essential, we also include the resonant type, primarily in case of possible elevated temperature events. A set of ion?neutral collision frequency coefficients for calculating the conductivity is summarized, including other particle pairs, in the Appendices. Small corrections to the traditional coefficients are made. Ieda (2020), JGR, https://doi.org/10.1029/2019JA027128 | ||
| 7/10 | Sung-Hong Park | An Observational Test of Solar Plasma Heating by Magnetic Flux Cancellation |
| Abstract : Magnetic flux cancellation in the solar photosphere has been studied with respect to various types of reconnection signatures in the upper solar atmosphere. Recently, Priest et al. (2018) proposed an analytic model for magnetic reconnection and consequent coronal heating, driven by a pair of converging and cancelling magnetic sources of opposite polarities on the photosphere. This model allows us to estimate the height and amount of magnetic energy released as heat at a reconnecting current sheet. In this talk, I will present a small-scale flux cancellation event observed by NASA's Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS). In particular, I will show how valid the proposed reconnection model is by comparing between the observations and model estimations. | ||
| 7/3 | Chae-Woo Jun | ElectroMagnetic Ion Cyclotron (EMIC) waves in the magnetosphere observed by the Arase and Van Allen Probes. |
| Abstract : Electromagnetic ion cyclotron (EMIC) waves, one kind of plasma waves in the magnetosphere, are generated at the magnetic equator due to ion cyclotron instability of energetic resonant ions. They play an important role in the loss of energetic electrons of the radiation belts particles into the upper atmosphere by pitch-angle scattering. In this talk, we will present recent statistical results of EMIC waves based on the Van Allen Probes (RBSP) and Exploration of energization and Radiation in Geospace (Arase) observations in 2017-2018. We will show that the occurrence of EMIC waves has a significant dependence on geomagnetic conditions, as well as their wavebands and background electron density. EMIC waves are more frequently observed at L>6 with higher occurrence rates (> 10 %) compared to those at L < 6. He-band EMIC waves at higher density regions are dominantly observed at 10-20 MLT during the main phase and substorm intervals, indicating that the major drivers of these waves are injected energetic particles from the magnetotail and enhanced ring current particles. H-band EMIC waves at lower density regions have two peak occurrence regions at 10-14 MLT at L~7-8 during the recovery phase and at 4-8 MLT at L>:8 during the non-storm intervals. Some He-band EMIC waves are also observed at lower density regions at L>8 during the non-storm intervals. These conditions are not sufficient for only using ion cyclotron instability to excite EMIC waves, meaning that we need additional generation processes such as mode conversion from other plasma waves. We will introduce the wave analysis method and present EMIC wave properties (e.g., wave power, polarization sense, wave normal angle, and center frequency) under various conditions. | ||
| 6/26 | Kawai Toshiki | Energy distribution of small-scale flares derived using genetic algorithm |
| Abstract : ULF Pc1 waves (0.2-5Hz) are continuous geomagnetic pulsations and have been observed across the whole magnetosphere and ionosphere as well as on the ground with different characteristics. These waves are known to be generated sporadically in the inner-magnetosphere as a result of ion cyclotron instability, so that these are generally accepted as electromagnetic ion cyclotron (EMIC) waves. Typically, Pc1 waves propagate along the magnetic field line as shear Alfvén mode in the magnetosphere. But, once the waves enter the ionosphere, they undergo mode conversion to the compressional (or magnetosonic) mode due to high conductivity, and they propagate across the magnetic field through the ionospheric duct (or waveguide). Ionospheric ducting is a way that the radio waves can travel thousands of kilometers along an ionospheric layer. Ducting is controlled by various physical processes and ionospheric conditions, among which plasma density is one of the factors. In this seminar, we show some observations of the ducting Pc1 wave in the ionosphere and its dependence of ionospheric plasma density from the observations of Swarm satellites and ground-based magnetometers. According to the ideal magnetohydrodynamics (MHD) theory, the compressional ULF wave can be accompanied by density perturbation of ionospheric plasmas. This means ULF Pc1 wave is not only affected by ionospheric plasma but also controls it by generating plasma density oscillations. We also show the observation of plasma density oscillations driven by ULF Pc1 waves from multiple satellites and ground-based observation. | ||
| 6/19 | Hyangpyo Kim | Study on the ULF Pc1 wave at low-Earth orbit: Propagation and effect on the ionosphere |
| Abstract : To understand the mechanism of coronal heating, it is crucial to derive the contribution of small-scale flares, the so-called nanoflares, to the heating up of the solar corona. To date, several studies have tried to derive the occurrence frequency distribution of flares as a function of energy to reveal the contribution of small-scale flares. However, there are no studies that derive the distribution with considering the following conditions: (1) evolution of the coronal loop plasma heated by small-scale flares, (2) loops smaller than the spatial resolution of the observed image, and (3) multiwavelength observation. To take into account these conditions, we introduce a new method to analyze small-scale flares statistically based on a one-dimensional loop simulation and a machine learning technique, that is, genetic algorithm. First, we obtain six channels of SDO/AIA light curves of the active-region coronal loops. Second, we carry out many coronal loop simulations and obtain the SDO/AIA light curves for each simulation in a pseudo-manner. Third, using the genetic algorithm, we estimate the best combination of simulated light curves that reproduce the observation. Consequently, the observed coronal loops are heated by small-scale flares with energy flux larger than that typically required to heat up an active region intermittently. Moreover, we derive the frequency distribution with a power-law index of approximately 2.02 in the energy range of 10^{25.5} < E < 10^{27.5} erg, which supports the nanoflare heating model. In contrast, we find that 90% of the coronal heating is done by flares that have energy larger than 10^{25} erg. | ||
| 6/5 | Sandeep Kumar | Comparative study of plasma and field in inner magnetosphere during magnetic storms using Arase observation and RAM-SCB simulations |
| Abstract : Geomagnetic storms are the most important component of space weather studies. During a geomagnetic storm, global depressions in the horizontal component (H) of geomagnetic field are observed. This depression in H is mainly caused by the westward ring current encircling the Earth around ~2-7 RE. The storm time distribution of ring current ions in the inner magnetosphere depend strongly on their transport in evolutions of electric and magnetic fields along with acceleration and loss. We compared the magnetic field and ion (H+, He+, and O+) and electron variations during geomagnetic storms using Arase observations for electrons by LEPe, MEPe and ions by LEPi and MEPi with the self-consistent inner magnetosphere model: Ring current Atmosphere interactions Model with Self Consistent magnetic field (RAM-SCB) [Jordanova et al., 2015]. We investigated magnetic and electric field taken from Arase observations and RAM-SCB simulation along Arase orbit during different phases of geomagnetic storms. We also compared pressure distributions of H+, He+, O+ and electron from the RAM-SCB simulation and associated ground ∆H deviations to investigate which species contribute the magnetic field deformation. | ||
| 5/29 | Masuda Satoshi | Microwave and Hard X-ray Solar Flare Observations by NoRH/NoRP and RHESSI |
| Abstract : We will introduce initial results from a statistical study of solar microwave and hard X-ray flares jointly observed over the past two solar cycles by the Nobeyama Radio Polarimeters (NoRP), the Nobeyama Radio Heliograph (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 non-thermal 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 that 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 are selection to source morphologies with the radio emission from the top of the are 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. The extend of the linear correlation over four orders of magnitudes suggests that magnetic fields within the 17 GHz source are restricted to a surprisingly narrow range for all flares. | ||
| 5/22 | Nakamura Satoko | Modeling of Japanese Geomagnetically induced current (GIC) and 2. Observations of EMIC rising tones in the Earth's inner magnetosphere |
| Abstract :
1. GIC is hazardous to social infrastructures having long‐length conductors such as power lines, pipelines, and communication cables. We evaluate geomagnetically induced currents (GICs) flowing in the Japanese power grid during severe space weather by using several methods. First, the three dimensional distribution of the geomagnetically induced electric field (GIE) was calculated by using the 3D finite-difference time-domain (FDTD) method. Second, we calculated the GICs flowing in a simplified 500 kV power grid network in Japan. Finally, we derive transfer functions between the GIC observation at 4 substations in Japan and the geomagnetic field recorded at the Kakioka station. 2. Electromagnetic ion-cyclotron (EMIC) waves are currently the subject of extensive investigations by the space physics community because of their importance with respect to electron and ion dynamics in the inner magnetosphere. Contrary to the existing understanding of EMIC waves, we have revealed that EMIC rising-tones are common phenomena strongly affecting the magnetospheric dynamics. We present that the depletion of relativistic electrons caused by EMIC rising tones in a timescale of a few minutes. A possible explanation of the loss process taking place in a time scale shorter than 1 minute and limited region of ~1 h MLT around noon due to the precipitation through the nonlinear resonant with EMIC rising tones. |
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| 5/15 | Hayakawa Hisashi | Extreme Space Weather Events Reconstructed from Analog Archival Records |
| Abstract : For the modern civilization, studies on extreme space weather events are more than just academic interests, due to its increasing impact to the modern civilization, which is increasingly dependent on the technological infrastructure. The Carrington event in 1859 September has been considered as as one of their most extreme cases, both in terms of the amplitude of the associated magnetic storm and the equatorward boundary of the associated auroral oval. However, it is not readily clear where the Carrington event is located within the history and range of the extreme space weather events. Here, this talk compares the storm intensity of the Carrington event with those of other extreme space weather events during the coverage of analog observations after mid-19th century, in terms of the equatorward boundary of the auroral oval based on available eyewitness auroral records. The comparison shows that the Carrington event was probably one of the most extreme storms, but not likely unique. As such, this talk will show what kind of scientific discussions we can derive from the analog archival records during the early scientific observations. | ||
| 5/8 | Kitahara Masahiro | Theory and simulation of wave-particle interactions between energetic electrons and whistler-mode chorus emissions （ホイッスラーモードコーラス放射と電子の相互作用に関する理論と計算機実験 ） |
| Abstract : Chorus emissions composed of coherent whistler mode waves are responsible for pitch angle scattering of energetic electrons. This scattering is closely related to energetic electron precipitation into the atmosphere, contributing to pulsating auroras. Conventionally, precipitating energetic electrons are considered to satisfy the cyclotron resonance condition over the energy range of a few to tens of keV and are scattered toward the loss cone by waves. However, previous simulation studies indicate that low pitch angle electrons tend to be scattered away from the loss cone by coherent whistler mode waves. We examine the mechanism of anomalous trapping at low pitch angles, deriving a particle set of equations of the motion of electrons with low pitch angle assumptions. An additional term that is conventionally neglected represents the Lorentz force caused by the wave magnetic field and the parallel particle velocity. Therefore, due to the Lorentz force caused by the large parallel velocity and the wave magnetic field, low pitch angle electrons satisfying the cyclotron resonant condition are scattered away from the loss cone and effectively trapped by waves. We perform test particle simulations in a one-dimensional dipole magnetic field with a whistler mode wave model and reproduce the anomalous trapping of electrons. The simulation results show that the majority of electrons at high and moderate pitch angles are scattered toward low pitch angle regions, while low pitch angle electrons are strongly scattered toward high pitch angle regions. Consequently, a coherent chorus element produces a bump in the electron pitch angle distribution. | ||
| 4/24 | Imajo Shun | Auroral arc powered by accelerated electrons from very high altitude |
| Abstract : Bright, discrete, and thin auroral arcs are a typical and fascinating form of auroras in the nightside polar region. These auroras emit light from ionospheric atoms or molecules particles excited by magnetospheric electrons accelerated by the quasi-static electric field being aligned with the earth’s magnetic field. The electrons gain the energy of several kilo electron bolts and reach at about 100 km in altitude. The potential gradient accelerating the electrons is considered to lies in the magnetosphere just above the ionosphere, typically 2000–15000 km in altitude. However, what the altitude the field-aligned acceleration of electrons starts from is still an open question. Here we show that the auroral arc is powered by electrons accelerated from further than 30000 km. Our observations of particles and fields were performed by the Arase satellite at 30000 km in altitude magnetically connected to the auroral arc observed by a THEMIS all-sky imager. We found evidence of electron accelerations by quasi-static parallel electric fields both above and below the spacecraft: monoenergetic downgoing electron beam, lack of upgoing electron due to loss into the ionosphere, upgoing proton beam, lack of downgoing proton, upward field-aligned current, converging perpendicular electric field, and electron density depression inferred from spacecraft potential. These results demonstrate that the potential drop region extends to very high altitude much higher than expected. The background plasma and magnetic field conditions above 30000 km are quite different from the conventional low-altitude acceleration region. It is necessary to consider a different generation mechanism of the parallel electric field for the very high-altitude acceleration. | ||
| 4/17 | Kanya Kusano | Introduction to Integrated Studies Seminar and the Challenge to Physics-based Prediction of Giant Solar Flares (総合解析セミナーへのお誘いと巨大太陽フレアの物理ベース予測への挑戦) |
| Abstract : The solar-terrestrial environment is a complex system that consists of nonlinear, non-equilibrium, and multi-scale interacting processes. The research in the Integrated Studies Division aims at improving our understanding of the dynamics of various phenomena in the solar-terrestrial environment through data analyses and 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 recent progress in flare prediction study. Solar flares are catastrophic explosions in the solar corona and may potentially cause a severe space weather disaster. However, because the onset mechanism of solar flares is not yet well elucidated, most of the flare forecasts in operation rely on empirical methods. We recently developed a physics-based model, called the κ-scheme, to predict solar flares for the first time through the critical condition of magnetohydrodynamic (MHD) instability triggered by magnetic reconnection. An analysis of the largest solar flares in solar cycle 24 indicates that the κ-scheme can precisely predict imminent giant solar flares with a small exception. Through this study, we discovered that the magnetic twist flux density in the vicinity of the magnetic polarity inversion line (PIL) on the solar surface plays a crucial role in determining when, where, and how large solar flares may occur. | ||