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。
|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|
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.
|5/20||Satoko Nakamura||Are geomagnetically induced currents (GICs) really a threat for the Japanese power grid?|
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
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.
|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|
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.|